# BloomWX — Full Learn Library > Plain-text export of every weather-explainer guide from BloomWX, suitable for AI ingestion. > See https://bloomwx.com/llms.txt for the index of URLs. This document contains the full body text of every /learn/ page on bloomwx.com, concatenated below in a stable order. Each topic begins with its source URL on a comment line so you can cite back to the live page. # SPC Convective Outlooks (TSTM/MRGL/SLGT/ENH/MDT/HIGH) The Storm Prediction Center (SPC) issues a Convective Outlook for Day 1 (today), Day 2 (tomorrow), and Day 3 (day after tomorrow), grading severe-weather potential into one of six categories from "general thunderstorms" to "high risk." ## The six risk categories - **TSTM (General Thunderstorms)**: Non-severe storms expected, but no organized severe risk. - **MRGL (Marginal, 1 of 5)**: Isolated severe storms possible. - **SLGT (Slight, 2 of 5)**: Scattered severe storms expected. - **ENH (Enhanced, 3 of 5)**: Numerous severe storms; widespread damage possible. - **MDT (Moderate, 4 of 5)**: Significant severe weather likely. This is the day you cancel plans. - **HIGH (5 of 5)**: Major severe outbreak; catastrophic impacts possible. A "Marginal" day does not mean "no risk." A weak SLGT day with poor timing has produced fatal tornadoes. The category indicates coverage and confidence, not the severity of any single storm. SPC also publishes specific probability maps for tornadoes, hail, and wind separately. ## Common terms in SPC discussions The following glossary is drawn from word-frequency analysis of 100 recent SPC Mesoscale Discussions and Convective Outlooks. ### Storm types - **Supercell**: Long-lived rotating thunderstorm — produces most strong tornadoes and the largest hail. - **Discrete**: Storms developing as separate, isolated cells with clear air between them. Discrete supercells are the highest tornado threat. - **Cluster**: A group of storms moving together, often interacting. Damaging wind and hail dominate. - **MCS (Mesoscale Convective System)**: Large organized complex of storms covering hundreds of miles. Typical late-night summer convection. - **QLCS (Quasi-Linear Convective System)**: Long line of storms (squall line). Wind damage and brief tornadoes ("spin-ups") common; sustained tornadoes rare. - **Bow echo**: Curved, bowed-out radar signature within a QLCS — sign of intense damaging winds. - **Splitting storm**: A supercell that divides into a right-mover (typically tornadic) and left-mover (typically hail-dominant). - **Embedded**: Smaller cells contained within a larger area of rain or convection. ### The ingredients - **CAPE**: Convective Available Potential Energy — the fuel. How much energy is available for an updraft. Higher = stronger storms. Units J/kg. - **CIN**: Convective Inhibition — the lid. Energy a parcel must overcome to reach free convection. - **MLCAPE / SBCAPE / MUCAPE**: CAPE for Mixed-Layer (average), Surface-Based (afternoon storms), and Most-Unstable (elevated convection at night) parcels. - **Lapse rate**: How fast temperature drops with altitude. Steep lapse rates = unstable atmosphere = vigorous updrafts. ~8 °C/km is a typical severe value. - **Cap / Lid**: Warm layer aloft that suppresses convection. "Cap breaks" = convection initiates. - **Boundary layer**: Lowest ~1 km of the atmosphere where surface heating, moisture, and friction dominate. ### Wind structure - **Shear**: How wind changes with altitude — the basic ingredient for organizing storms. - **Bulk shear**: Magnitude of wind difference between two altitudes. "0–6 km bulk shear" is the standard severe-weather metric. - **SRH (Storm-Relative Helicity)**: Spin available to storms. 0–1 km SRH drives tornado potential; 0–3 km SRH drives general supercell organization. - **Hodograph**: Graph of wind speed and direction across heights — used for storm-mode prediction. - **Low-level jet (LLJ)**: Narrow band of fast winds 1–2 km above the surface, important for nocturnal storms. - **Veering**: Wind direction turning clockwise with altitude — favors supercells. ### Boundaries and synoptic features - **Trough**: Elongated area of lower pressure aloft. Provides lift and forcing for storms. - **Ridge**: Elongated area of higher pressure aloft. Generally suppresses storms. - **Shortwave**: Fast-moving disturbance in the upper-level flow — often the immediate trigger for an outbreak. - **Warm front / Cold front**: Boundaries where one air mass replaces another. Common storm initiation zones. - **Dryline**: Boundary between dry desert air and moist Gulf air, common over the southern Plains. One of the most prolific severe-weather producers in the US. - **Outflow boundary**: Surface boundary left behind by a previous storm's rain-cooled air. ### Storm dynamics - **Updraft**: Rising column of air inside a thunderstorm. Drives hail growth. - **Downdraft**: Descending column of air. Drives damaging wind and microbursts. - **Mesocyclone**: Rotating updraft inside a supercell. Tornado prerequisite (though not all mesos produce tornadoes). - **Mesovortex**: Small-scale rotation embedded in a QLCS. Source of brief spin-up tornadoes. - **RFD (Rear-Flank Downdraft)**: Downdraft on the back side of a supercell. RFD surge is often the immediate tornado trigger. ### Threats - **Large hail**: Hail ≥ 1" diameter (severe threshold). Significant = ≥ 2" (golfball+). - **Damaging wind**: Wind ≥ 58 mph (severe threshold). Significant = ≥ 75 mph. - **Tornado Watch**: SPC-issued box (typically 4–8 hours, multi-state) where tornadoes are possible. - **Severe Thunderstorm Watch**: Same shape but for hail/wind threat without strong tornado risk. - **STP (Significant Tornado Parameter)**: Composite combining CAPE, shear, helicity, and moisture; calibrated to highlight EF2+ environments. --- # SPC Mesoanalysis Explained Mesoanalysis is a real-time look at the atmospheric "ingredients" for severe weather, updated hourly by SPC. The four parameters most useful when assessing thunderstorm potential are MLCAPE, bulk shear, SRH, and the Significant Tornado Parameter. ## MLCAPE — Mixed-Layer CAPE (the fuel) Convective Available Potential Energy. Measures how much energy is available to thunderstorms in the lower atmosphere. Higher values = stronger updrafts = bigger storms. Units are J/kg. - < 500: Limited storm potential - 500–1000: Weak storms possible - 1000–2500: Typical for severe weather - 2500–4000: Significant severe potential - 4000+: Extreme conditions; very large hail likely ## 0–6 km Bulk Shear (the organization) How much the wind changes from the surface up to 6 km altitude. Higher shear lets storms tilt instead of collapsing on themselves, which keeps them alive longer and lets them rotate. Units are knots (kt). - < 30 kt: Storms stay disorganized - 30–40 kt: Organized multicell clusters - 40–50 kt: Supercells possible - 50+ kt: Strong supercells / wind events ## 0–1 km SRH — Storm-Relative Helicity (the spin) How much the wind direction twists from the surface up to 1 km. Storms ingesting this twist can develop a low-level rotating updraft (mesocyclone) — the source of most tornadoes. Units are m²/s². - < 100: Weak rotation potential - 100–200: Moderate; supercells possible - 200–300: Strong tornado environment - 300+: Significant tornado potential ## Significant Tornado Parameter (the composite) A single number that combines CAPE, shear, helicity, and low-level moisture. Designed to highlight environments where strong (EF2+) tornadoes are most likely. - < 1: Significant tornado unlikely - 1–3: Significant tornadoes possible - 3–6: Substantial tornado risk - 6+: High-end tornado environment (rare) --- # SPC Mesoscale Discussions Mesoscale Discussions (MDs) are the earliest formal "we're watching this" signal SPC issues — typically 30 to 90 minutes before a watch box drops. A meteorologist identifies a developing severe-weather threat and writes a short discussion explaining what they're concerned about, where, and how it might evolve. ## "Concerning..." line categories The header line of each MD summarizes the meteorologist's intent: - **Severe Potential**: Severe storms developing or expected. - **Tornado Watch likely**: A formal tornado watch is being prepared. - **Severe Thunderstorm Watch likely**: A severe-storm watch is being prepared. - **Watch X (continuation)**: Updates on conditions inside an active watch. ## Why this matters If you watch only formal warnings, you're reacting. MDs let you anticipate. When you see one over your area, the next 1–2 hours will likely bring a watch and then warnings. --- # Hazardous Weather Outlook (HWO) Each NWS Weather Forecast Office (WFO) issues a Hazardous Weather Outlook (HWO) once or twice a day. It's the local meteorologist's plain-language narrative of what hazards to expect over the next 7 days for the WFO's coverage area — different from SPC's national outlooks because it speaks to the specific terrain, season, and history of your region. ## What's in an HWO - **Day 1**: Detailed hazard outlook for today. - **Days 2–7**: General outlook with confidence levels. - **Spotter activation**: Whether SKYWARN spotter networks are expected to be activated and when. ## Why this matters SPC speaks nationally. The HWO speaks to the forecaster's specific local concerns — winter weather in a marginal-snow area, fog in valley terrain, marine hazards on the coast, etc. It often catches threats that national outlooks miss because those don't cross severe-storm thresholds. --- # Local Storm Reports (LSRs) Local Storm Reports (LSRs) are observations of severe weather as it happens — submitted by trained spotters, law enforcement, the public via Spotter Network and CoCoRaHS, and confirmed by the local NWS office. The dashboard pulls the last 48 hours of reports for a county and its surrounding counties. ## Common report types - **Tornado**: Confirmed tornado on the ground. - **Funnel Cloud**: Funnel observed but not in contact with the ground. - **Wall Cloud**: Lowering attached to a thunderstorm — possible tornado precursor. - **Hail**: Hail size reported, in inches (1.00" = quarter, 1.75" = golfball, 2.75" = baseball, 4"+ = softball). - **Wind / Gust**: Wind damage or measured gusts, in mph. - **Flash Flood**: Active flash flooding observed. - **Heavy Rain**: Significant rainfall amount reported. ## Note on accuracy LSRs come in from many sources of varying training. Hail and wind reports especially can over- or under-estimate. NWS verifies and revises reports for the official storm log, which lags real-time by hours to days. --- # How to Size Hail Accurate hail reports drive warnings, climatology, and damage assessment. Spotters mess this up the same way every time — they size hail by produce ("pea", "marble", "grape"). Those words don't mean anything specific. A "pea" can be anywhere from 1/4" (split pea) to 1/2" (snow pea), spanning an entire category in the NWS hail scale. Always report a diameter in inches if you can measure it; otherwise pick from the NWS standard reference list — not a custom one. ## NWS standard hail size reference These are the only comparison objects the NWS recognizes as consistent. Every Skywarn class teaches them. The key threshold is **1.00" (quarter)** — that's the trigger for a Severe Thunderstorm Warning. - **BB / pea — 0.25"**: Smallest reportable. NWS lists "pea" but recommends "BB" because pea sizes vary widely. - **Marble — 0.50"**: Common toy marble. - **Penny — 0.75"**: A penny is exactly 0.75". Reliable. - **Nickel — 0.88"**: 7/8". Just under the warning threshold. - **Quarter — 1.00"** ⚠ WARNING THRESHOLD: Severe Thunderstorm Warning issued at this size. - **Half-dollar — 1.25"**. - **Walnut / ping-pong — 1.50"**. - **Golf ball — 1.75"**: Often the cutoff for significant hail damage to roofing. - **Hen egg — 2.00"**. - **Tennis ball — 2.50"**. - **Baseball — 2.75"**: Modern "Destructive" / IBW Tag-2 threshold. Triggers Wireless Emergency Alerts. - **Tea cup — 3.00"**. - **Softball — 4.00"**: Very rare; over-reported. Verified extensively. - **Grapefruit — 4.50"**: Even rarer. - **DVD / CD — 4.75"**: Standard CD/DVD diameter, used as a "I have one in the car" reference. ## Why precision matters NWS warning text reflects the LARGEST reported size. Calling a baseball-sized stone "tennis ball" can be the difference between a destructive-tagged warning (which triggers Wireless Emergency Alerts on every phone in the path) and a routine warning. Calling quarters "marbles" misses the warning threshold entirely. ## How to report well 1. Wait for the storm to leave the area — getting hit by a baseball-sized stone for the sake of a report is bad math. 2. Photograph the largest stone next to a coin, ruler, or known-size reference (CD/DVD trick works well). 3. Report two sizes: "majority quarter, largest golf ball" gives the forecaster both the typical and peak. 4. Note the duration: 30 seconds of marbles vs. 10 minutes of nickels are very different damage profiles. 5. Skip "pea", "grape", "shooter marble", "jawbreaker" — none have standard sizes. ## Where to report - Call your local NWS office's spotter hotline directly. - Spotter Network if you're a registered SKYWARN spotter. - mPING app (free, iOS/Android) — public-facing weather report tool from NSSL. - Tweet @YourLocalNWS with photo + location. Reference: NWS Spotter Field Guide. --- # Cloud Identification — A Field Guide Clouds get sorted by altitude first — high, middle, low, vertical — and then by shape (heap, layer, wisp, anvil). The WMO has 10 main genera. The ones a storm spotter actually cares about — wall clouds, shelf clouds, mammatus — sit in their own taxonomy below the main 10. ## High clouds (above 20,000 ft) - **Cirrus (Ci)**: Thin wispy streaks ("mare's tails"). Ice crystals. Often the first sign a warm front is approaching ~24-48 hours out. - **Cirrocumulus (Cc)**: Small white tufts in patterns ("mackerel sky"). Rare, short-lived; signals upper-level instability. - **Cirrostratus (Cs)**: Thin transparent veil. Causes a halo around the sun or moon (ice-crystal refraction). Often precedes precipitation 12-24 hours. ## Middle clouds (6,500–20,000 ft) - **Altocumulus (Ac)**: Patches of "puffy" elements, gray or white. Morning Ac in summer often means thunderstorms by afternoon. - **Altostratus (As)**: Gray uniform sheet. Sun looks "watered down" through it. Often precedes steady precipitation. - **Nimbostratus (Ns)**: Thick dark gray layer actively producing precipitation. The classic "rainy day overcast." ## Low clouds (below 6,500 ft) - **Stratus (St)**: Featureless gray sheet, like elevated fog. Produces drizzle, mist, or light snow. - **Stratocumulus (Sc)**: Gray patches/rolls/lumps. Most common cloud worldwide. Light drizzle at most. - **Cumulus (Cu)**: Detached puffy "fair weather" clouds. Often grow vertically through the day. ## Vertical / convective - **Cumulus congestus / TCu**: "Towering cumulus" — vertical heap clouds with cauliflower tops. Transition between fair-weather Cu and Cb. - **Cumulonimbus (Cb)**: The thunderstorm cloud. Tower extends from low altitudes up to the tropopause. Anvil top spreads horizontally. Produces lightning, hail, heavy rain, microbursts, and rotation. ## Storm-spotter clouds - **Wall cloud**: Localized lowering attached to the rain-free base of a thunderstorm, usually under the updraft. Can rotate. Tornadoes most often form from rotating wall clouds. - **Funnel cloud**: Visible rotating column descending from a wall cloud, NOT touching the ground. Becomes a tornado on contact OR if dust is being kicked up directly below it. - **Shelf cloud (arcus)**: Wedge-shaped cloud along the leading edge of a gust front (cold outflow). Looks dramatic but is NOT tornadic — it's straight-line wind. - **Roll cloud**: Horizontal tube-shaped cloud detached from the parent storm. Forms in stable air ahead of an outflow boundary. Rare and photogenic. - **Mammatus**: Pouch-like protrusions hanging UNDER a storm anvil. Sign of very turbulent air. NOT directly tornadic but indicates intensity. - **Tail cloud**: Horizontal cloud band extending from a wall cloud toward the precipitation core. Indicates inflow. - **Beaver tail**: Flat smooth horizontal inflow band on the right-rear flank of a supercell. Long tongue-shaped — looks like its namesake. Indicates a strong organized supercell. ## Wall vs shelf cloud — the most-confused pair - **Wall cloud**: Localized, under the rain-free base, may rotate, ahead of where rain is falling. Forms in INFLOW air. Tornado risk. - **Shelf cloud**: Long horizontal wedge, at the leading edge of rain, kicked up by OUTFLOW air, doesn't rotate. Straight-line wind only. Quick test: which way is the wind blowing under it? Inflow (toward the cloud) = wall cloud, possibly tornadic. Outflow (away from the cloud, gusting in your face from the storm) = shelf cloud, straight-line wind. ## Reference - NOAA JetStream Cloud Classification: noaa.gov/jetstream/clouds - NWS Spotter Field Guide: weather.gov/safety/thunderstorm-spotterguide - WMO International Cloud Atlas: cloudatlas.wmo.int --- # Reading a Skew-T Diagram A Skew-T (technically "Skew-T Log-P") is the chart meteorologists use to plot a vertical sounding of the atmosphere — temperature, dewpoint, wind, and humidity at every altitude from the surface to the stratosphere. It's the densest forecast tool in operational meteorology. Once you can read one, you stop guessing what the model is doing — you can see why. ## The chart's axes - **Horizontal axis**: Temperature in Celsius. The lines slant up and to the right (hence "skew-T") so the temperature traces stay within the chart area. - **Vertical axis**: Pressure in millibars (mb). 1000 mb at the bottom = sea level; 100 mb at top ≈ 50,000 ft. Logarithmic. ## The two main traces - **Red line — Temperature**: Air temperature at each altitude. Usually decreases with height (~6.5°C/km in the troposphere). - **Green/blue line — Dewpoint**: Dewpoint at each altitude. The CLOSER the dewpoint and temperature lines are, the more humid the layer. When they touch, you have saturation (cloud). Where the two traces are far apart, the layer is dry. Where they're close together or touching, the layer is moist or saturated. The shape of those near/far zones tells you where clouds form and where dry-air entrainment will eat into a storm. ## Wind barbs Down the right side of the chart you'll see wind symbols, one per altitude. Each barb shows wind speed (number of feathers) and direction (the line points the direction wind is FROM). Reading the wind profile from surface to ~6 km tells you about shear, which determines whether storms are pulse, multicell, or supercell. ## Big concepts - **CAPE** (Convective Available Potential Energy): Shaded area between the parcel temperature curve and the environmental temperature curve, ABOVE the LFC. Larger area = stronger updrafts. 1000-2500 J/kg = moderate; 2500+ = strong; 4000+ = extreme. - **CIN** (Convective INhibition): The "cap." Shaded area BELOW the LFC where the parcel is cooler than the environment. Strong cap prevents storm formation until something breaks it. - **LCL** (Lifting Condensation Level): Altitude where a rising surface parcel becomes saturated and forms a cloud base. Low LCL (≤1000 m AGL) often correlates with tornadic supercells. - **LFC** (Level of Free Convection): Once a parcel is lifted past this altitude, it accelerates upward on its own. Higher LFC = harder to initiate storms. - **EL** (Equilibrium Level): Top of the storm. Storms rarely punch through. Corresponds to anvil base. - **Inversion**: Layer where temperature INCREASES with height. Acts as a cap. The "cap" forecasters talk about is usually a low-level inversion at ~700 mb. ## What a forecaster looks at first 1. Surface conditions — temperature, dewpoint, wind at the bottom of the chart. 2. Cap strength — sharp warm-nose at 700-850 mb? If so, storms unlikely until convergence/heating breaks it. 3. Moisture profile — dewpoint and temperature traces close in the low levels (humid)? Then divergent in mid-levels (dry-air aloft, the "loaded gun" sounding)? 4. Shear profile — do the wind barbs change direction with height (directional shear) and increase in speed (speed shear)? Both needed for supercells. 5. CAPE — eyeball the size of the positively-buoyant area. ## The classic "loaded gun" supercell sounding - Surface: warm, moist (dewpoint ≥ 65°F) - 700 mb: dry-air intrusion (T-Td > 15°C) — fuels evaporative cooling for storm downdrafts - Wind: SE at surface → S aloft → SW at 500 mb → W in jet stream (clockwise turning = "veered" = positive shear for tornadic supercells in the Northern Hemisphere) - CAPE: 2000-4000 J/kg - CIN: small but present (cap that breaks in the afternoon) ## Where to find them - SPC Observed Soundings: spc.noaa.gov/exper/soundings — every 12 hours from radiosonde launch sites - University of Wyoming Sounding Archive: weather.uwyo.edu/upperair/sounding.shtml — historic + current, with computed indices - SPC Mesoanalysis: spc.noaa.gov/exper/mesoanalysis — model-derived soundings for any point in the U.S. --- # WPC Surface Analysis Charts The Weather Prediction Center (WPC) draws this every three hours. It's the closest thing modern meteorology has to the "weather map" you remember from a TV broadcast — pressure highs and lows, fronts, squiggly isobars, station observations plotted in their familiar circle-with-flag format. Spotters use it for the synoptic context that radar can't give you. ## The fronts - **Cold front (blue, triangles)**: Cooler, drier air pushing into warmer, moister air. Triangles point in the direction the front is moving. Squall lines and severe storms most often fire along or just ahead of these. - **Warm front (red, half-circles)**: Warmer air over-running cooler air. Half-circles point in the direction of motion. Brings overrunning precip, often steady rain, fog, low cloud bases. - **Stationary (alternating)**: Front not moving. Useful as a focus for repeated convective initiation in the same place — flash flood setups love stationary fronts. - **Occluded (purple)**: A cold front has caught up to a warm front. The warm sector is gone aloft; the surface low is mature and usually weakening. - **Dryline**: Boundary between dry desert air and moist Gulf air. Texas / Oklahoma classic. Severe weather initiation hotspot. - **Trough / outflow boundary**: Dashed line. Not a true front; just a wind shift / convergence axis. Often where new convection pops. ## The pressure features - **Big H (high)**: Center of high pressure. Sinking air, generally fair weather, light winds at the surface, clearer skies. Wind blows clockwise around it (Northern Hemisphere). - **Big L (low)**: Center of low pressure. Rising air, generally cloudy/precipitation, stronger winds. Wind blows counter-clockwise. Severe storms often develop in the warm sector to the south/east. - **Isobars**: Lines of equal pressure (the squiggles). Tightly-packed isobars = steep pressure gradient = strong winds. Loose isobars = light winds. - **Pressure values**: In millibars (mb), shorthand. "1024" near a high is normal, "984" near a deepening low is impressive. Below 980 mb in the central US is a serious storm. ## Station observations (the circles) Each plotted circle is one METAR station. The fill of the circle is sky cover (open = clear, half = partly cloudy, full = overcast). Numbers around the circle are temp (top-left), dewpoint (bottom-left), and pressure (top-right, last 3 digits — "024" = 1024.0, "873" = 987.3). The line with feathers is wind direction + speed. ## What spotters look for - Where am I relative to the warm sector? South/east of the surface low, between the warm and cold fronts. That's where severe storms fire. - Is the dryline in play? Look for a sharp temperature/dewpoint gradient over short distance — Texas Panhandle through western Oklahoma in spring is the classic setup. - How tight is the pressure gradient? Tight isobars across the storm-threat area mean strong low-level winds — feeds shear, helps initiate. - Where are the boundaries from yesterday's storms? Outflow boundaries (dashed lines) are convective initiation magnets the next day. WPC analyses live at wpc.ncep.noaa.gov; new analysis every 3 hours. --- # GOES Water Vapor Satellite Imagery Water vapor satellite is the single most useful product for seeing the upper atmosphere. The GOES-19 ABI sensor measures radiation in the 6.2 μm channel — a wavelength water vapor absorbs strongly. Bright/white = lots of moisture aloft. Dark = very dry. Where bright meets dark, things happen. ## What you're looking at - **Bright white / cyan**: High-altitude moisture. Cold cloud tops (anvils, cirrus shields), strong ascent. - **Gray**: Mid-level moisture. Steady-rain regimes, broad warm-air advection. - **Brown / dark**: Very dry air aloft. Sinking air, the dry slot of a developing storm, the deep-layer dry punch behind a cold front. - **Black / very dark**: Stratospheric air being pulled down — often along the back edge of a digging trough. Indicates strong dynamics. ## The features to spot - **Jet streak**: A bright/dark gradient that streams across the chart, often bowed. The right-entrance and left-exit regions of jet streaks force ascent — both are favored for thunderstorm development. - **Dry slot**: A wedge of dark air wrapping into a developing surface low. Marks the dry punch of mid-level air being entrained into the system. When a dry slot pokes into the warm sector, severe weather often follows along its leading edge. - **Comma cloud / head**: The bright comma-shaped cloud mass curling around a deepening low. Classic mid-latitude cyclone signature. - **MCS / convective complex**: A bright blob covering several states overnight in summer. Indicates a mature mesoscale convective system — often produces flooding rain and damaging wind. - **Tropical plume**: A bright streak from the deep tropics arcing into the US. "Atmospheric river" in the West, "Gulf moisture surge" in the Plains. Drives heavy precip events. ## Why spotters care Severe weather lives at the boundary between bright and dark on water vapor. The dark-to-bright transition shows where dry air is being pulled into the system; convection thrives at that interface. If you're watching a cap-busting setup, watching the dry slot push into the warm sector is the visual confirmation that the atmosphere is overturning. Source: NESDIS GOES-19 CONUS at star.nesdis.noaa.gov; updates every 5 minutes. --- # CPC 6–10 / 8–14 Day Outlooks Once the NWS 7-day forecast runs out, the Climate Prediction Center (CPC) takes over. The 6–10 day and 8–14 day outlooks don't give you a high temperature for next Tuesday — they give you a probability that the period will be warmer (or wetter) than normal. Different question, different chart. ## What the colors mean The maps shade probability of "above normal" or "below normal" for the period as a whole. White areas mean equal chances. Saturated color = high confidence; pale color = lean. - **Red (temperature)**: Above-normal temperature favored. Deeper red = higher confidence. - **Blue (temperature)**: Below-normal temperature favored. - **Green (precip)**: Above-normal precipitation favored. - **Brown (precip)**: Below-normal precipitation favored. - **White / EC**: Equal chances — no clear signal in either direction. Means the model spread is wide enough that "near normal" is the safest bet. ## What "normal" means The 1991–2020 climatology for the same calendar window. So a "70% chance of above-normal temps" outlook for late May means warmer than the 1991–2020 average for late May at that location — not warmer than today, not warmer than the long-term record. Useful for energy / agriculture / scheduling, not so useful for "should I bring a jacket Tuesday". ## The two products side by side - **6–10 day**: Days 6 through 10 from issuance. Bridges the gap between the deterministic NWS 7-day and the longer outlooks. This one usually has the most skill. - **8–14 day**: Days 8 through 14. Wider window, lower confidence, more "EC" (white) coverage. Still useful for season-aware planning. ## How to use it operationally - Don't read it as a daily forecast — it's a period probability. - Do use it for planning irrigation, fire-weather staffing, or "is the next cold snap likely to be a thing?" - Watch the change — outlooks issued on consecutive days often shift. A region that flips from "above normal precip" to "equal chances" in 24 hours tells you the operational forecasters lost confidence in the wet pattern. - Pair with the 30-day / 90-day for a fuller picture — CPC publishes monthly and seasonal outlooks too. Source: cpc.ncep.noaa.gov; new outlook issued daily around 3 PM Eastern. --- # US Drought Monitor The US Drought Monitor is a weekly snapshot of where drought is — and how bad. It's a joint product from USDA, NOAA, and the National Drought Mitigation Center, and it's the official reference for federal drought declarations, crop insurance, and disaster relief. Updated every Thursday at 8:30 AM Eastern. ## The five drought categories - **D0 — Abnormally Dry (yellow)**: Not officially drought. Going into drought (recovering ground after a wet spell, or beginning to dry out). Crop growth slowed; some short-term water deficit. - **D1 — Moderate Drought (tan)**: Some damage to crops/pastures. Streams, reservoirs, wells low. Voluntary water-use restrictions requested. - **D2 — Severe Drought (orange)**: Crop or pasture losses likely. Water shortages common. Mandatory restrictions imposed. - **D3 — Extreme Drought (red)**: Major crop / pasture losses. Widespread water shortages. - **D4 — Exceptional Drought (dark red)**: Exceptional / widespread crop losses. Shortages of water in reservoirs, streams, and wells creating water emergencies. Rare classification. ## What it considers Not just rainfall. The author considers: - Precipitation deficits (multiple time scales: 30 / 90 day, 6 / 12 month, multi-year) - Soil moisture (modeled and remote-sensed) - Streamflow and reservoir levels - Vegetation health (satellite-derived, NDVI etc.) - Local field reports from observers in each state ## Why spotters / EMA care - **Fire weather context**: D2+ areas are the regions where Red Flag Warnings hit hardest — fuels are already cured. - **Flash flood risk paradox**: Areas freshly out of drought, or in early D0/D1, can flash-flood more readily than their rainfall would suggest. Hard, dry ground sheds water before it can infiltrate. - **Severe weather climatology**: Persistent drought in the Plains often goes hand-in-hand with strong cap setups, which produce explosive late-day convection when something finally breaks the cap. - **Disaster declarations**: County-level D2+ status is a trigger for federal emergency management programs. Source: droughtmonitor.unl.edu; updated every Thursday at 8:30 AM Eastern. --- # WPC Quantitative Precipitation Forecast (QPF) QPF stands for **Quantitative Precipitation Forecast**. Where the regular forecast says "30% chance of rain Tuesday," QPF answers "and how much?" The Weather Prediction Center contours expected rainfall accumulations over set forecast windows — 24, 48, 72, 120, and 168 hours out — in inches of liquid equivalent. ## The contours Each colored band is a rainfall accumulation range for the entire forecast window. So on the 5-day chart, "2.0″" means "two inches of rain are expected to fall here over the next five days" — not per day. - **Light green**: Trace to ~0.25" — drizzle / light shower territory. - **Green**: 0.25" to 1" — typical rainstorm. - **Yellow / orange**: 1" to 2" — heavy rain, possible localized flooding. - **Red**: 2" to 4" — flash flood risk in rapid-runoff areas. - **Pink / purple**: 4"+ — significant flood event likely. ## What spotters / EMA care about - **Antecedent conditions**: 1.5" of QPF on already-saturated ground floods. The same 1.5" on dry hard ground mostly runs off — into creeks. Drought Monitor + QPF together tell you which scenario you're in. - **Training**: If multiple QPF cycles in a row keep painting the same red bullseye over the same county, storms are "training" — repeatedly firing over the same place. That's how flash flood disasters happen. - **Snow ratios**: QPF is liquid equivalent. For snow, multiply by the snow ratio (10:1 typical, 15-20:1 in cold dry events). 0.5" QPF in winter could mean 5–10" snow. - **Compare cycles**: Watch how QPF changes between issuances. A bullseye that jumps from 1.5" to 3" in 12 hours means forecasters got more confident in a heavy event — pay attention. ## The available windows - **Day 1 (24 hr)**: Highest skill. What's expected today. - **Day 2 (48 hr)**: Tomorrow. - **Day 3 (72 hr)**: Three-day total. Useful for "this storm system's overall rainfall." - **5-day (120 hr)**: Best for "what does the next work week look like?" - **7-day (168 hr)**: Edge of useful skill. Use as a trend, not gospel. Source: wpc.ncep.noaa.gov/qpf/qpf2.shtml. Multiple issuances per day. --- # NWS HeatRisk HeatRisk is a newer NWS product that combines forecast temperature, local climatology, and known health-impact thresholds into a single five-level scale. It answers "is this hot day actually dangerous for people in this place?" — which a raw temperature can't, because 95°F in Phoenix and 95°F in Maine are very different threats. ## The five HeatRisk levels - **0 — Green**: No elevated risk. Typical for the location and season. - **1 — Yellow**: Minor risk. Hotter than normal — watch out for heat-sensitive folks (elderly, young children, outdoor workers). - **2 — Orange**: Moderate risk. Affects most heat-sensitive people; impacts on outdoor labor + sports. - **3 — Red**: Major risk. Affects anyone without effective cooling and/or hydration. Heat-related illness likely. - **4 — Magenta**: Extreme risk. Rare, long-duration heat with little/no overnight relief. Health system impact level. ## Why it's better than just temperature - **Climatology-aware**: A 90°F day in Maine in May is HeatRisk 3 because nobody's acclimated yet. The same 90°F in Maine in late August is HeatRisk 1. - **Duration-aware**: A 95°F single day is risk 2; the same 95°F sustained across a week with warm nights is risk 3 or 4. Cooling overnight matters as much as the daily peak. - **Health-data-anchored**: The thresholds are calibrated against CDC heat-mortality data, not just "this temperature feels uncomfortable." - **Includes the whole day**: Overnight low temps + humidity factor in. A 100°F afternoon with a 78°F dewpoint and a 79°F overnight low is far worse than a 100°F afternoon with a 60°F dewpoint and a 65°F overnight low. ## What spotters / EMA do with it - **Cooling center activation**: Most county EMAs activate cooling centers at HeatRisk 3+. - **Outdoor event planning**: Sports, parades, festivals — HeatRisk 3+ usually triggers schedule changes. - **Welfare checks**: Days at risk 3+ for several consecutive days typically prompt door-to-door checks on elderly residents. - **Roof / pavement workers**: OSHA increasingly references HeatRisk for required work-rest cycles. Source: wpc.ncep.noaa.gov/heatrisk/graphics.html. Day 1–7 maps issued daily by NWS. The product is also being adopted by CDC for public-health messaging. --- # NHC Tropical Weather Outlook The National Hurricane Center publishes Tropical Weather Outlooks ("TWOs") four times a day during hurricane season (May 15 – Nov 30 Eastern Pacific, Jun 1 – Nov 30 Atlantic). The map shows where existing or potential tropical systems are, color-coded by NHC's confidence that they'll develop into a depression / storm in the next 48 hours and 7 days. ## The colored shapes - **Yellow X / area**: Low chance (less than 40%) of tropical cyclone formation in the next 7 days. - **Orange X / area**: Medium chance (40–60%). - **Red X / area**: High chance (greater than 60%). Pay attention. - **Hurricane symbol (red spiral)**: Active named tropical cyclone. Intensity + track are on a separate page (the NHC track cone). ## The 7-day vs 2-day outlook NHC publishes both. The 2-day is what you'd use for "should I be watching this thing today?" The 7-day is what you'd use for planning ("am I going to need to start moving boats / boarding up / advising my coastal county next week?"). The 7-day was added in 2023 — older procedures may still reference only the 5-day version. ## What spotters / EMA do with it - **Pre-positioning**: Yellow areas in the Gulf of Mexico in August trigger early warning of resource positioning. Orange areas trigger pre-positioning. Red areas trigger activation. - **Early-stage tracking**: Once a system has a yellow / orange / red blob over it, watch the NHC discussion text for guidance on which models are converging. - **Atlantic vs Pacific basins**: Both have separate outlooks. East Pacific impacts Mexico and the desert SW (via remnant moisture). West Pacific is a separate JTWC product. - **This product is not the cone**: Once a system is named, the cone of uncertainty (separate product) replaces the colored blob in operational decision-making. Source: nhc.noaa.gov. Updated four times daily (2 AM, 8 AM, 2 PM, 8 PM Eastern) during hurricane season; suspended outside the season. --- # GOES IR & GeoColor Satellite GOES-19 is the East-coast geostationary satellite. The Advanced Baseline Imager (ABI) on board has 16 channels — different wavelengths revealing different things. We surface two of them on the Charts tab in addition to water vapor: GeoColor (the "looks like the planet" picture) and IR (the cloud-top temperature picture that works at night). ## GeoColor A composite product designed to look like a true-color photo during the day. After dark it shifts to a "city lights" base map with the IR cloud overlay tinted blue. Visually intuitive — you can see snow cover, vegetation, smoke plumes, and (at night) urban lights. Best for general situational awareness. ## IR (Band 13, 10.3 µm) Measures the temperature of cloud tops. The colder the cloud top, the higher it is — and the higher it is, the stronger the updraft producing it. NWS and SPC color-enhance this channel so cold tops (severe storm anvils) jump out. - **Gray / white**: Warm cloud tops — low clouds, fog, stratus. Often nuisance fog or marine layer. - **Light yellow**: Mid-level cloud tops — typical thunderstorm tops. - **Orange**: Cold tops (around -50°C) — strong thunderstorm. - **Red / pink**: Very cold tops (below -60°C) — severe / supercell territory. - **White / black (deepest)**: Extreme cold tops (below -75°C) — overshooting tops, often severe weather producers. ## What spotters look for - **Overshooting tops**: Small bumps above the anvil where the updraft punches through the tropopause. Indicates a very strong updraft. Often coincides with severe weather at the surface. - **Cold-U / V signature**: A V-shaped pattern of warm air downwind of the overshooting top — sign of a mature supercell with a strong updraft. - **Anvil expansion rate**: Anvils expanding rapidly = strong, organized convection. Slow = weakening. - **Convective initiation**: First small cumulus puffs in clear air on visible / GeoColor often precede storm development by 30–60 minutes — useful for chasing. Source: NESDIS GOES-19 at star.nesdis.noaa.gov. Updates every 5 minutes; full disk + sector views available. --- # MRMS Rotation Tracks MRMS — Multi-Radar Multi-Sensor — is the NSSL system that merges every NEXRAD site's data into one seamless mosaic. The Rotation product takes this a step further: it computes **azimuthal shear** at every grid point and tracks the maximum value over rolling time windows. That gives you a post-event "where was the rotation?" map, not just a now-cast. ## The time windows From the Product Type list, pick "Rotation," then choose a rolling window from the right-side menu: - **Instantaneous (ROT)**: Right-now azimuthal shear. Useful in real time, but flickers as scans cycle. - **30-min max**: Smoothed track of rotation in the last half hour. The most useful operational view. - **1-hour max (ROT_60M)**: BloomWX's deep-link default. Captures most cyclic supercells' track within a typical chase. - **2-hour max**: Wider window — useful for storms that have just exited a county, where you want to see what passed through. - **24-hour max**: Post-event survey view. Did the warned rotation actually track where the warning polygon was? - **7-day max**: Climatological / event-period summary. Rare but useful for outbreak retrospectives. ## The color scale - **Green**: Weak shear (~0.005 / s). Often non-meteorological or marginal supercell rotation. - **Yellow**: Moderate shear. Mid-level meso, low-end significant. - **Orange**: Strong shear. Significant rotation; possible / likely tornado warning territory. - **Red**: Very strong shear. Tornadic supercell range. - **Purple / pink**: Exceptional shear. Strong-tornado producers. ## What it's NOT - **Not a tornado track.** Rotation aloft doesn't guarantee a tornado at the surface. The track shows where the radar saw rotation; whether that rotation reached the ground is determined by storm survey + LSRs. - **Not a real-time warning tool.** The product has a small latency. Use NWS warnings for life-safety decisions. - **Not great close to the radar.** Within ~10 km of a NEXRAD site, cone-of-silence + range-folding artifacts can produce false rotation signals. - **Not perfect at long range.** Beyond ~150 km from a radar, beam height grows and weak rotation gets lost above the surface circulation. ## How spotters / EMA actually use it - **Post-event verification**: "Did the warned rotation track over the area where damage was reported?" Pair with LSRs. - **Cyclic supercell tracking**: A storm that produces multiple tornadoes typically shows multiple discrete rotation tracks separated by gaps where the meso was occluding and re-organizing. The 1-hour view makes those cycles obvious. - **QLCS spin-up identification**: Brief tornadoes embedded in a squall line show as small, fast-moving rotation maxima. Easy to miss in real time; obvious in the 1-hour track. - **Damage survey planning**: Before driving out for an NWS damage survey, the 24-hour rotation track tells you where to focus. Source: mrms.nssl.noaa.gov/qvs/product_viewer/. BloomWX deep-links to the 1-hour rotation max. The viewer is interactive. --- # Wildfire Smoke + AQI (AirNow Fire and Smoke Map) The Charts tab links to AirNow's Fire and Smoke Map — the official EPA + NOAA + USFS consumer view of wildfire impacts on air quality. It blends three layers: real-time PM2.5 from regulatory + community sensors, NIFC active wildfire pins, and NESDIS HMS satellite-derived smoke plumes drawn over the top. ## The three layers - **Colored circles**: Air quality (AQI) at PM2.5 sensor locations. Same EPA color scale as the dashboard's AQI panel — green is good, red+ is unhealthy. Sensors include both regulatory monitors and consumer (PurpleAir) stations. - **Fire icons (flame)**: Active wildfires from the National Interagency Fire Center (NIFC). Click for size, name, containment percentage. - **Gray smoke shading**: NESDIS HMS satellite-detected smoke plumes — actual smoke seen from space in the past 24 hours. Light gray = thin / aloft, dark gray = thick / lower. ## Why this view (and not just "HRRR-Smoke") HRRR-Smoke is the model that *forecasts* smoke 18-48 hours out. AirNow Fire and Smoke shows what's *happening right now*, derived from sensors and satellite. For most spotter / EMA decisions ("should we activate the cooling center? is the air bad enough to cancel football?") the live observation is what you want. NOAA's GSL is also deprecating the old HRRR-Smoke web page in favor of a new viewer (DESI), and the AirNow page is more stable for everyday use. If you want the explicit forecast model rather than observations, DESI has the HRRR-Smoke layer once you navigate to it. ## How to use it operationally - **Cooling-center / shelter activation**: Use the colored AQI circles in your county. Red or worse → activation common; purple/maroon → mandatory in most jurisdictions. - **Outdoor event calls**: Sports, school recess, outdoor work. Pair the AQI circles with the gray smoke overlay — if there's smoke aloft headed your way, AQI may worsen during the event. - **Trans-regional smoke awareness**: Canadian wildfires affecting the upper Midwest, California fires reaching Colorado — the HMS satellite layer makes the long-range transport visible at a glance. - **Sensor cross-checks**: If a single sensor reads wildly different from neighbors, it's often a localized issue (a backyard burn pile, a sensor next to an A/C exhaust). Trust the cluster average. - **Spotter situational awareness**: Smoke aloft attenuates radar (reduces echo strength) and makes visible-channel satellite less useful. The HMS smoke layer warns you when this is in play. ## Caveats - **Sensor coverage gaps**: Rural areas may have no sensors within 50 miles. Use the satellite smoke layer as a fallback. - **Consumer sensors run high**: PurpleAir-style stations report higher PM2.5 than EPA monitors during heavy smoke. AirNow applies a correction but the calibration isn't perfect. - **HMS is observed, not forecast**: If you need to know "what's smoke going to be like tomorrow," check DESI or the HRRR-Smoke model directly. - **Indoor air**: Indoor concentrations with HVAC + MERV filters typically run 20–40% of outdoor on smoky days. Source: fire.airnow.gov. Forecast model: sites.gsl.noaa.gov/desi (DESI / HRRR-Smoke). --- # HRRR Forecast Composite Reflectivity The High Resolution Rapid Refresh (HRRR) is a 3-km convection-allowing model that NOAA runs every hour out to 18-48 hours. "Forecast composite reflectivity" is the model's simulated radar — what NEXRAD *would see* if the forecast plays out as expected. Useful for "will this storm hold together until it reaches my county?" or "how quickly will the squall line arrive?" ## What the colors mean Same scale as the live NEXRAD composite — model reflectivity is calibrated to look like real radar: - **Light green**: Light rain. - **Yellow**: Moderate rain / weak storm. - **Orange**: Strong storm, possibly small hail. - **Red**: Intense storm, likely hail. - **Magenta**: Extreme — large hail / supercell core. ## Reading the forecast hours Each "fh" in the viewer is the forecast hour (hours from initialization). fh=0 is the model analysis (best estimate of "now"). fh=6 is what the model thinks reflectivity will look like 6 hours from the run time. Loop through the hours to watch the forecast evolve. - **fh=1 to 6**: Best skill window. Storm placement and timing usually within ~30 min and ~30 km of reality. - **fh=6 to 12**: Good for general "will it happen here?" planning. Specific cell timing less reliable. - **fh=12 to 18**: Trends only. Whether convection happens is reliable; exactly where + when is not. - **fh=18 to 48**: Extended HRRR runs (00, 06, 12, 18 UTC only). Treat as guidance, not prediction. ## What spotters / EMA do with it - **Pre-storm intercept planning**: The forecast tells you where storms are likely to fire and how they'll move. Pair with the SPC outlook to pick chase regions hours in advance. - **Squall line timing**: Look at the forecast loop to see when the line crosses your county. EMA uses this for "when will warning sirens likely sound" planning. - **Storm mode forecasting**: Discrete cells in the forecast (separated supercells) vs a solid line vs a broken cluster — different storm modes mean different threat profiles. - **Confidence-checking the SPC outlook**: If the forecast shows almost nothing inside an Enhanced Risk area, something's off. ## The big caveat HRRR is good but not perfect. Common failure modes: it tends to **over-develop convection** in marginal environments (storms in the forecast that don't fire in reality), and it can **misplace storms by 30-50 km** in environments with weak forcing. Compare the latest 2-3 model runs — if they agree, confidence is high; if they disagree, the forecast is less reliable. Source: tropicaltidbits.com/analysis/models/?model=hrrr&pkg=ref_frzn (BloomWX deep-links here for the radar-like view). Other free viewers: pivotalweather.com and mag.ncep.noaa.gov. New HRRR run every hour. --- # GOES GLM and NOAA LightningCast — Lightning Imagery BloomWX surfaces two lightning products on the Charts tab — both free, both satellite-derived, but answering different questions. **GLM** shows where strikes happened in the last few minutes. **LightningCast** predicts where strikes will happen in the next 60 minutes. ## GOES Geostationary Lightning Mapper (GLM) GLM is an instrument on GOES-19 (and GOES-18 for the West) that continuously photographs the Earth in a narrow optical band where lightning emits brightly (777.4 nm). It detects both cloud-to-ground AND in-cloud strikes — the latter being where most of the actual lightning in a thunderstorm lives. - **Bright yellow / red**: High flash density in the last minute. The storm core. - **Orange**: Moderate flash density — active convection but not the most-intense cell. - **Sparse points**: Isolated strikes. Storm starting up, decaying, or anvil-only. - **No color**: No detected flashes (or the storm is below GLM's detection threshold). ### How GLM compares to ground networks - **Detects more total flashes** than NLDN / ENTLN — GLM sees in-cloud strikes that ground networks miss. - **Lower spatial precision** — ~8 km at nadir vs sub-kilometer for ground networks. - **1-2 minute latency** from strike to image. Ground networks publish in seconds. - **Free + global** — no subscription. Ground networks like Vaisala NLDN are subscription-only. - **Best use**: "is there lightning in this region?" Not "exactly where is the next strike going to be?" ## NOAA LightningCast (60-min probability forecast) LightningCast is a NOAA / CIMSS / NSSL AI model that takes the current GOES satellite imagery (visible, near-IR, long-wave IR) and predicts the probability of lightning at each pixel over the next 60 minutes. It's been used operationally by NWS forecasters since 2021. - **Yellow contour (≥10%)**: Lightning possible somewhere in the next hour. - **Orange (≥40%)**: Lightning likely. Most NWS offices issue Special Weather Statements at this threshold for outdoor venues. - **Red (≥75%)**: Lightning near-certain. Take cover if outdoors. ## How spotters / EMA actually use them - **Storm initiation**: LightningCast often signals 15–45 min BEFORE the first strike. Useful for outdoor-event evacuation calls. - **Storm intensity**: GLM flash rate jumping from sparse to a bright cluster usually precedes severe weather (hail spike, intensifying updraft). - **Storm decay**: GLM going dark = storm collapsing. The downburst hazard often peaks during this transition. - **Anvil lightning**: Strikes well outside the rain core ("bolt from the blue") — GLM catches these; you're at risk under a bright anvil even on a dry sidewalk. - **Outdoor event "30/30" rule**: Suspend if thunder within 30 sec of flash (~6 mi). LightningCast lets you anticipate; GLM lets you confirm. Sources: NESDIS GOES-19 GLM at star.nesdis.noaa.gov, CIMSS LightningCast viewer at cimss.ssec.wisc.edu/probsevere/lc/. For genuine strike-by-strike data (life-safety grade), the commercial ground networks (Vaisala NLDN, Earth Networks ENTLN) are the operational standard — BloomWX recommends RadarScope or RadarOmega Pro tiers, which embed those feeds. --- # Nearby County Alerts (Rings) Active NWS alerts in counties surrounding yours, organized by how close they are. Severe weather often crosses county lines on a predictable path — a tornado warning in the next county west of you may be heading your way within minutes. ## Ring definitions - **Ring 1**: Counties directly bordering your selected county. - **Ring 2**: Counties one step removed (your neighbors' neighbors). ## Why this matters SKYWARN spotters and EMA volunteers track what's coming toward them, not just what's overhead. Watching nearby alerts gives you 15–60 minutes of lead time vs. waiting for your own county to be added to the warning polygon. Direction arrows on alert badges (↑ N, → E, etc.) show which direction each affected county sits relative to you. --- # Fire Weather Outlooks SPC's daily Fire Weather Outlook identifies areas where the combination of low humidity, strong wind, and dry vegetation creates elevated wildfire risk. Day 1 and Day 2 include forecaster discussion text; Day 3 and the multi-day Day 3–8 outlook are image-only. ## Risk categories - **Critical**: Likely Red Flag conditions; rapid fire growth possible. - **Elevated**: Increased risk but below Red Flag thresholds. - **Isolated Dry Thunder**: Thunderstorms expected with little or no rain — lightning-ignition risk. ## Related NWS products - **Red Flag Warning**: Critical conditions are imminent or occurring. Outdoor burning is typically prohibited. - **Fire Weather Watch**: Critical conditions possible in 12–72 hours. Time to prepare. ## What drives fire weather - **Low humidity** (typically below 25%): Reduces moisture in vegetation, faster ignition. - **Strong wind** (15+ mph sustained): Pushes fires faster, harder to contain. - **Dry fuels**: Drought-stressed grass, brush, timber from extended dry periods. - **Atmospheric instability**: Makes fire behavior erratic and creates fire-induced winds. ## Why it matters even outside fire-prone regions Red Flag conditions can develop in the Midwest, Northeast, and Mid-Atlantic during droughts. Many large fires start as agricultural burns, debris fires, or campfires that escape during these windows. The forecast text often includes specific guidance on burn restrictions. --- # How to Read NEXRAD Radar The NEXRAD composite is the live, mosaiced view from multiple Doppler radar sites. The colors show **reflectivity**, which roughly indicates precipitation intensity. Your county is outlined in blue. ## Reflectivity colors - **Light green**: Light rain (drizzle to light shower). - **Green**: Moderate rain. - **Yellow**: Heavy rain / start of thunderstorm intensity. - **Orange**: Heavy thunderstorm, possibly small hail. - **Red**: Intense storm, likely hail. - **Magenta/Pink**: Extreme — large hail almost certain. - **Light blue**: Snow (different intensity scale). ## Colored polygons Active NWS warnings, watches, and advisories shaded by event type — red for tornado warnings, orange for severe thunderstorm, etc. ## Pinned icons Local Storm Reports from the last 24 hours: red triangles = tornadoes, blue circles with numbers = hail (size in inches), green diamonds = wind (speed in mph), teal squares = flooding. ## Limitations NEXRAD beams curve up with distance. Beyond ~150 miles, the beam is high enough that low-level features (light rain, snow at the surface) get missed. The composite has small seams between contributing radars and lower resolution at long range. ## Honest note: this is a free radar feed BloomWX renders a free composite NEXRAD layer (Iowa Environmental Mesonet / RainViewer tiles). It updates roughly every 5 minutes, which is fine for situational awareness and SKYWARN spotting from a fixed location. It is *not* the right tool if you're driving toward a storm. For active storm chasing — making intercept decisions on rotation, debris signatures, or velocity couplets — pay for a real radar app: - **RadarScope** (dtn.com/radarscope): what every spotter and chaser I know runs. Single-site Level 2/3, velocity, dual-pol products, storm tracks. ~$10/yr basic, ~$100/yr Pro Tier 2 with MRMS and lightning. - **RadarOmega** (radaromega.com): modern competitor with a slick UI and good MRMS / TDS overlays. - **GR2Analyst / GRLevel3** (grlevelx.com): desktop, used by media meteorologists and serious chasers. Steeper learning curve but unmatched product depth. BloomWX has no affiliate relationship with any of these — they're recommended on merit. Use the free dashboard radar to monitor the broader picture; switch to a paid single-site app the moment you're inside the warning polygon or moving toward one. --- # River and Stream Flood Gauges USGS river and stream gauges measure the height and flow of water at a fixed point and report back every 15 minutes. Color tells you the current flood status; numbers tell you exactly where things stand. ## Status colors - **Normal**: Within historical normal range for this date. - **Above Normal**: Elevated but no flooding expected. - **Action Stage**: Monitor closely; low-lying areas may see impacts. - **Minor Flood**: Minor flooding (typical: roads, parking lots, fields). - **Moderate Flood**: Moderate flooding (homes, businesses, road closures). - **Major Flood**: Major flooding (significant damage, evacuations). ## Stage vs discharge vs percentile - **Stage**: Height of the water, in feet above an arbitrary reference (NAVD88, ft AGL, or local datum). Easy to picture but not directly comparable between rivers. - **Discharge**: Volume of water flowing past, in cubic feet per second (cfs). Directly comparable across rivers — 10,000 cfs in a small creek is more dramatic than 10,000 cfs in the Mississippi. - **Percentile**: Where current flow ranks against the historical record for this date. "85th percentile" means 85% of recorded values for this day-of-year were lower. Useful for spotting drought (low percentile) and unusual high flows (high percentile). ## Why this matters Flash floods kill more Americans most years than tornadoes or hurricanes. Even small streams can rise from "normal" to "minor flood" within a couple of hours during heavy rain, and gauges give you real lead time to act. --- # Air Quality Index (AQI) The U.S. Air Quality Index (AQI) is EPA's standard for reporting air quality on a 0–500 scale. Lower is cleaner. Each value maps to a color and a health-impact category. ## Six health categories - **0–50 Good**: Air quality is satisfactory; little or no risk. - **51–100 Moderate**: Acceptable for most; unusually sensitive may have minor effects. - **101–150 Unhealthy for Sensitive Groups**: Sensitive groups should limit exertion. - **151–200 Unhealthy**: Everyone may experience effects. - **201–300 Very Unhealthy**: Health alert; everyone should avoid prolonged exertion. - **301+ Hazardous**: Emergency conditions; avoid all outdoor exertion. ## The pollutants - **PM2.5**: Fine particulate matter (soot, smoke). The most-tracked pollutant; what wildfire smoke loads on you. Penetrates deep into lungs and bloodstream. - **PM10**: Coarser particles (dust, pollen). Less harmful per-microgram than PM2.5 but still problematic at high levels. - **Ozone (O₃)**: Ground-level ozone — formed by sunlight + NOₓ reactions. Primary smog component on hot, sunny days. - **NO₂**: Nitrogen dioxide — combustion byproduct, mostly traffic and power plants. - **SO₂**: Sulfur dioxide — coal/oil combustion, refineries, volcanic activity. - **CO**: Carbon monoxide — vehicle exhaust and incomplete combustion. The dashboard shows per-pollutant breakdowns so the operator can see which pollutant is driving the overall AQI on a given day. ## Source The dashboard uses Open-Meteo's CAMS-based AQI feed. Same EPA scale as AirNow, but Open-Meteo provides global coverage where AirNow has US-only ground stations. Breakpoints from EPA AQI Technical Assistance Document. --- # METAR / ASOS / AWOS Observations The dashboard shows METAR observations from the nearest 2–3 ASOS / AWOS automated stations at airports near your county. METAR is the international standard for surface weather observations, issued every hour (and more frequently as SPECIs when conditions change rapidly). ## Why airport stations? ASOS/AWOS are the gold standard. Properly sited, calibrated, and QC'd around the clock. They're more reliable than citizen weather stations (CWOP) but less dense, so the dashboard shows both. ## Why three stations instead of one? Comparing stations lets you watch a boundary cross. If the dewpoint drops at the western station 20 minutes before the eastern one, you just watched a dryline pass — invisible from a single METAR. The raw METAR text codes look cryptic but are universal — every pilot and meteorologist parses them the same way. --- # Space Weather: R, G, S Scales NOAA's Space Weather Prediction Center (SWPC) classifies space-weather events on three scales — Radio blackout (R), Geomagnetic storm (G), and Solar radiation storm (S) — each running 1 to 5. Most space-weather data is global (the Sun affects all of Earth roughly the same), with the exception of the aurora forecast which is computed per-county. ## R-scale — Radio blackout Driven by solar X-ray flares. The flare ionizes Earth's upper atmosphere within minutes, disrupting HF (high-frequency) radio propagation on the sunlit hemisphere. - R1: Minor — minor HF degradation on sunlit side. - R2: Moderate — limited HF blackout, some loss of contact. - R3: Strong — wide-area HF blackout, low-frequency navigation degraded. - R4: Severe — HF blackout most of sunlit Earth for hours. - R5: Extreme — complete HF blackout entire sunlit side. Who cares: amateur radio operators (SKYWARN nets, emergency comms), aviation HF over oceans/polar routes, maritime communications, military. ## G-scale — Geomagnetic storm Earth's magnetic-field disturbance, usually triggered by a CME impact or high-speed solar wind. Driven by the planetary K-index (Kp), 0–9. - G1 (Kp 5): Minor — aurora at high latitudes, minor grid fluctuations. - G2 (Kp 6): Moderate — aurora to mid-latitudes; high-latitude HF noise. - G3 (Kp 7): Strong — voltage corrections needed; GPS error grows; aurora to ~50°N. - G4 (Kp 8): Severe — widespread voltage problems; HF radio sporadic; aurora to ~45°N. - G5 (Kp 9): Extreme — grid systems can fail; aurora as far south as Florida/Texas. Who cares: power-grid operators, GPS-dependent industries (precision agriculture, surveying, drones), pipeline operators, satellite ops, aurora chasers. ### K-index (Kp) — the underlying number Kp is the global summary number for geomagnetic activity, derived every 3 hours from a network of magnetometers. Each whole step is roughly a 2× jump in disturbance — so Kp 6 isn't just "one more" than Kp 5, it's twice as energetic. - **Kp 0–2**: Quiet — no magnetic disturbance worth mentioning. - **Kp 3**: Unsettled — minor wobble, no operational impact. - **Kp 4**: Active — elevated geomagnetic activity below storm threshold; aurora possible at very high latitudes (Alaska, northern Canada). - **Kp 5**: Storm onset (G1) — aurora visible at high latitudes; minor grid noise. - **Kp 6+**: Significant storm (G2+) — aurora pushes to mid-latitudes; real grid + GPS effects. SWPC issues "ALERT/WARNING: Kp X" messages whenever Kp crosses an observed or forecast threshold (most commonly Kp 4, 5, 6, 7, 8). Kp 4 alerts on the Solar tab mean the magnetic field is restless but not yet in storm territory — an early heads-up that conditions could escalate, not an action signal for mid-latitude operators. ## S-scale — Solar radiation storm Energetic protons accelerated by solar events. Rare but consequential. - S1: Minor — minor impacts to HF in polar regions. - S2: Moderate — some polar HF degradation; airlines may reroute. - S3: Strong — astronauts shelter; total HF polar blackout. - S4: Severe — satellite single-event upsets common. - S5: Extreme — complete polar HF blackout for days. ## Solar wind metrics - **Bz**: Interplanetary magnetic field component along Earth's magnetic axis. Sustained negative (southward) Bz lets solar wind couple to Earth's magnetosphere — the precursor to geomagnetic storms. Bz ≤ −10 nT for ≥ 30 minutes is a textbook storm signal. - **Bt**: Total magnetic field strength. - **Speed**: Solar wind speed in km/s. Background is 350–450 km/s; high-speed streams ≥ 600 km/s drive moderate G-storms; CME shocks can push speeds past 1,000 km/s briefly. - **Density**: Proton density (protons/cm³). Pressure spikes at CME arrivals. ## Coronal Mass Ejections (CMEs) Massive bursts of plasma and magnetic field ejected from the Sun. Take 1–3 days to reach Earth. The CME pipeline panel shows analyzed CMEs from NASA's DONKI catalog with predicted arrival times and Kp impact — the most actionable advance warning we can give for grid/comms/GPS preparation. ## SDO imagery — different wavelengths show different layers - **Visible (HMI)**: White-light view of the photosphere — sunspots visible as dark patches. - **304 Å (chromosphere)**: Helium emission from the lower atmosphere — filaments, prominences, flare ribbons. - **171 Å (corona)**: Iron emission from the million-degree corona — active region loops, coronal holes. - **Magnetogram (HMIB)**: Black-and-white map of magnetic polarity (white = north, black = south). Sunspot complexes show as bipolar pairs. --- # Astronomy Terms Explained Sky observation uses some specific vocabulary that's not always intuitive. Here are the most-used terms in BloomWX's astronomy panel. ## Brightness - **Magnitude**: Apparent brightness on an inverted scale — lower numbers are brighter. Sirius is mag −1.5; Venus can reach −4.9 at peak; the dimmest naked-eye stars under truly dark skies are about mag 6. Each step of 1 magnitude = 2.5× the brightness. ## Sky coordinates - **Altitude**: Angle above the horizon. 0° = right at the horizon, 90° = directly overhead. Most observers can see down to about 10° before trees, buildings, or atmospheric extinction get in the way. - **Azimuth**: Compass direction. 0° = N, 90° = E, 180° = S, 270° = W. ## Meteor showers - **ZHR (Zenithal Hourly Rate)**: Meteors per hour you would see if the radiant were directly overhead, under perfectly dark sky. Real counts are always lower — light pollution, low radiant altitude, and Moon brightness cut into ZHR. - **Radiant**: Constellation the meteors appear to fly out from. The meteors themselves can streak across any part of the sky — they all just trace back to the radiant. - **Parent body**: The comet or asteroid whose debris stream Earth crosses to produce the shower. ## Planet events - **Opposition**: When Earth is between an outer planet and the Sun. The planet is closest to Earth, brightest in the sky, and visible all night. Best observing window for outer planets. - **Greatest elongation**: When Mercury or Venus reaches its maximum apparent distance from the Sun, making it easiest to spot during morning or evening twilight. Mercury's elongations top out around 28°, Venus around 47°. - **Conjunction**: When two planets, a planet and the Moon, or a planet and a bright star appear close together in the sky. ## Eclipses - **Partial eclipse**: Earth or Moon only partly enters the shadow. - **Total eclipse**: Earth or Moon fully enters the umbra (deepest shadow). Total solar eclipses produce the brief "totality" famous for daytime darkness; total lunar eclipses turn the Moon red ("blood moon") for an hour or more. - **Annular**: "Ring" eclipse — happens when the Moon is at apogee (farther from Earth) so it appears too small to fully cover the Sun. - **Penumbral**: Moon passes through Earth's outer shadow only. Subtle dimming, easy to miss. ## Twilight - **Civil twilight**: Sun 0–6° below horizon. Sky is bright enough to see comfortably; brightest planets and stars are visible. - **Nautical twilight**: Sun 6–12° below horizon. Horizon visible at sea; many stars visible. - **Astronomical twilight**: Sun 12–18° below horizon. Sky still has a slight glow; some faint deep-sky objects washed out. - **True night**: Sun more than 18° below horizon. Sky fully dark — only window for serious deep-sky observation. ## Rocket launch geometry - **Pad bearing**: Compass direction from your county to the launch pad. - **Peak elevation**: Approximate maximum elevation angle of the rocket from your location, assuming an 80 km MECO altitude. Beyond ~1,000 mi the plume drops below the horizon. - **NET (No Earlier Than)**: Earliest possible launch time. Real launch may slip later (weather, technical holds). --- # Planetary Alignments and Planet Parades A planetary alignment — popularly called a "planet parade" — is when several of the naked-eye planets cluster within a small arc of sky as seen from Earth. The planets are not literally lined up in 3D space; they stay in their own orbital lanes. They just appear close together along the same band of sky, the ecliptic. ## Two definitions — and which one BloomWX uses - **Geocentric conjunction**: Planets close together in our sky as seen from Earth. THIS is what BloomWX surfaces in the alignments list. Observable events — step outside on the date and you'll see them. - **Heliocentric alignment**: Planets on roughly the same ray out from the Sun in 3D space. Visible in an orrery view but not necessarily in our sky, because Earth's own orbital position matters. The Solar System Map at the top of the Astronomy tab shows this view. BloomWX surfaces sky conjunctions because they're real observable events. The two views often disagree: planets that line up in 3D around the Sun aren't necessarily close together in our sky. The math: take the geocentric ecliptic longitude of each visible planet, find the smallest arc that holds them all (or a subset of 2+), and report that as the conjunction width. ## The five visible planets Mercury, Venus, Mars, Jupiter, and Saturn. These are the planets bright enough to see with the naked eye from a typical suburban sky. Uranus and Neptune are technically planets too, but Uranus needs a dark sky and Neptune needs a telescope, so they are left out of "alignment" reckoning by convention. ## Tightness tiers - **Tight (≤30° arc)**: Fist-width spread. Stunning to see — all five planets readable in a single binocular sweep along the horizon. Only a handful per decade. - **Compact (≤60° arc)**: About a constellation wide. Anyone can see they're grouped. You'll catch a few of these a year. - **Broad (≤90° arc)**: Quarter of the sky. The looser end of what news outlets still call a "planet parade." Common — several per year. ## How to observe a planet parade Most parades line up along the ecliptic — the same arc the Sun and Moon trace across the sky. - **Evening parades**: Planets visible after sunset. Look west or southwest 30–60 minutes after sunset. - **Morning parades**: Planets visible before sunrise. Look east or southeast 60–30 minutes before sunrise. - **Both**: When 5+ planets are involved, you may catch the inner planets (Mercury, Venus) at twilight and the outer planets (Mars, Jupiter, Saturn) higher in the sky. The BloomWX Astronomy tab includes a top-down solar-system orrery with a timeline slider. Drag the slider to the alignment date to see the planet dots cluster on the same side of the Sun. ## Common misconceptions - **"Planets cause earthquakes / tides / weather"**: No. Planetary alignments have no measurable gravitational or electromagnetic effect on Earth — the Moon and Sun dominate by many orders of magnitude. - **"True alignments only happen every X centuries"**: Depends entirely on what you mean. Loose visible parades happen yearly; strict heliocentric alignments of all 8 planets within tight tolerance happen roughly every 170 years. - **"You need a telescope to see one"**: No — the visible planets are all naked-eye objects. Binoculars help in twilight when Mercury is hugging the horizon, but a telescope is overkill. --- # CWOP Citizen Weather Stations CWOP is the Citizen Weather Observer Program — a network of personal weather stations operated by hobbyists, schools, businesses, and citizen scientists. Stations report through APRS to NOAA's data ingest, where the observations feed into surface analysis and verification. ## Strengths - **Density**: Many more stations than ASOS/AWOS — useful for spotting micro-scale features. - **Real-time**: Reports every few minutes vs. hourly METAR. - **Hyper-local**: A station two blocks from you reports your neighborhood's conditions. ## Cautions - **Quality varies**: Siting and calibration are owner-dependent. A station next to an A/C exhaust will read warmer. - **Less reliable than ASOS**: Use METAR (Surface obs panel) as your gold standard; CWOP fills in the gaps. ## Identifying stations The callsign you see (e.g. EW6362, KG5WBN) is the station's APRS identifier — ham radio operators reuse their callsigns; civilian stations are issued a code. Click any station to see its detail page on aprs.fi (the standard CWOP/APRS portal). --- # School and Business Closings Closings are sourced differently depending on your area: - **Chicago metro (LOT WFO)**: Live aggregated feed from the Emergency Closing Center (ECC) — schools, businesses, government, religious organizations. Updated continuously during winter and severe events. - **Other markets**: A link out to the local TV station or newspaper that maintains the closings list for that market. The dashboard pre-checks these URLs every 6 hours and swaps in a fallback link if the primary 404s. ## Why this varies by market Each TV station's closings system is custom-built and rarely exposes a public feed. The Chicago metro is unusual because three competing stations (WGN, ABC7, Fox32) all subscribe to the Emergency Closing Center, which does publish a feed. --- # BloomWX Push Notifications BloomWX can send a notification to your phone or computer when NWS issues a severe-weather warning for the county you subscribed to. The notification arrives even if BloomWX isn't open — same look and feel as a text or any other app notification — and tapping it opens the live county dashboard. ## How it works Web Push is a built-in browser feature (Chrome, Firefox, Edge, Safari 16.4+). When you subscribe, your browser hands BloomWX an opaque endpoint URL it uses to deliver pushes. BloomWX's server polls NWS every 60 seconds; when a Tornado / Severe Thunderstorm / Flash Flood Warning fires for your county, the server posts the alert to the push provider (Apple, Google, or Mozilla, depending on your browser), which delivers it to your device. ## What gets sent By default, the four life-safety warnings: - **Tornado Warning** — active tornado threat - **Tornado Emergency** — confirmed catastrophic tornado - **Severe Thunderstorm Warning** — damaging wind / large hail imminent - **Flash Flood Warning** — active life-threatening flooding A future update will let you opt into watches and lower-impact products. Today, we keep it tight to avoid notification fatigue. ## What it's NOT BloomWX push is a **convenience layer**, not a life-safety primary channel. There's a 1–2 minute upper bound on delivery latency (NWS poll interval + push-provider relay), and BloomWX's server can fail silently during outages. For the actual life-safety job, two things matter more: - **NOAA Weather Radio**: A SAME-capable receiver tuned to your local transmitter alerts in seconds, no internet needed. The gold standard. - **Wireless Emergency Alerts (WEA)**: Government-sent broadcasts to every cell phone in a polygon. Enabled by default on most phones; verify in Settings → Notifications → Government Alerts. BloomWX push complements those. Don't use it as your only warning channel. ## iPhone / iPad note iOS Safari requires BloomWX to be installed as a Home Screen app (Share → Add to Home Screen) before push alerts can be subscribed. Open the home-screen icon, then the Subscribe button on the Feed tab will work. Android, Mac, Windows, and Linux: works directly from any browser tab. ## Privacy Subscribing creates no account and asks for no personal info. BloomWX stores only the opaque push endpoint your browser generates plus the county you subscribed to. No email, no name, no IP. Unsubscribe deletes the record. --- # NOAA Weather Radio (NWR) NOAA Weather Radio All-Hazards (NWR) is a nationwide network of about 1,000 government-operated VHF radio transmitters that continuously broadcast NWS forecasts, observations, and severe-weather warnings 24/7, with no ads and no internet dependence. When a tornado or flash-flood warning is issued, an NWR receiver in your house alerts in seconds — even if your power, cell tower, or cable modem is down. ## The seven channels (162.400–162.550 MHz) Every NWR transmitter operates on one of seven frequencies. A SAME-capable radio scans all seven and locks onto the strongest one for your location. The BloomWX dashboard's NWR panel tells you which channel your nearest transmitter uses. - Channel 1: 162.400 MHz - Channel 2: 162.425 MHz - Channel 3: 162.450 MHz - Channel 4: 162.475 MHz - Channel 5: 162.500 MHz - Channel 6: 162.525 MHz - Channel 7: 162.550 MHz ## SAME — Specific Area Message Encoding Most modern NWR receivers support SAME, which lets you program your radio with your county's six-digit FIPS code so the alarm only fires for warnings in your specific area — not every county the transmitter covers. Without SAME you'd get woken up by warnings 60 miles away; with SAME you only hear about your own county. SAME codes are the same as the 5-digit FIPS county code with a leading zero (e.g. McHenry, IL = 017111). The radio's manual walks through the program-county step. ## Why a real radio matters even in 2026 - **Survives outages**: NWR works during power, cell, and ISP failures — the exact times severe weather usually hits. - **Sub-second alerting**: NWR fires the moment NWS issues the warning. Apps and dashboards (including BloomWX) poll every 30–60 seconds and add internet latency on top. - **No subscription, no battery drain on your phone**: Receiver runs on AC + batteries; phone stays available for calls and texts. - **Backed by the federal government**: No third-party platform decides whether you receive the alert. ## Hardware to look for Pick a SAME-capable receiver with battery backup. Three good options at different price points: - **Midland WR-120**: Desktop SAME radio, ~$30. The standard recommendation. Battery backup, alert tones for warnings. - **Midland WR-400**: Same engine as WR-120 plus a louder alarm and an alert-color LED. ~$60–$70. - **Midland HH54VP2**: Handheld portable SAME receiver. Useful if you spend time outdoors / in a basement / camping. ~$50. ## Online streams — useful, but not a substitute Hobbyists and hobbyist-run sites (Broadcastify, YouTube live streams, etc.) relay NWR over the internet. They're handy for situational awareness but depend on someone's home scanner staying on, an ISP staying up, and the host's stream not getting throttled. They're a convenience layer, not a primary safety channel. --- # NWS DSS Briefing Packets DSS (Decision Support Services) is the NWS program that provides briefing materials to emergency managers, public safety officials, and event planners ahead of significant weather. The packet is a PDF prepared by your local NWS forecasters with current conditions, key threats, and confidence levels — written for non-meteorologists making operational decisions. ## When packets are issued - Severe weather events (tornado / severe-thunderstorm outbreaks expected) - Winter storms (heavy snow, ice, or extreme cold) - Tropical systems (hurricanes / tropical storms in the forecast cone) - Heat or cold extremes (multi-day heat waves, arctic outbreaks) - Major outdoor events (parades, festivals, etc.) ## What the dashboard shows When a packet is active, the dashboard displays the front-page thumbnail with a link to view the full PDF. Only the first page is rendered inline (the rest is dense meteorological detail aimed at trained users); the link opens the complete document. ## Citation When citing content from this document, attribute the source URL of the matching topic (listed at the top of each section). When citing weather data shown on a county dashboard, attribute the original source (NWS / SPC / USGS / NASA / etc.) — BloomWX aggregates and displays but does not produce the underlying data. ## License The dashboard interface and these explainers are © BloomWX. Underlying weather data is public domain (US government works).