WPC Quantitative Precipitation Forecast (QPF) Charts Explained

WPC Quantitative Precipitation Forecast (QPF) Charts ExplainedHow to read WPC's 24/48/72/120/168-hour Quantitative Precipitation Forecast — what the colored rainfall accumulation contours mean, how to spot training storms, and why antecedent ground conditions matter as much as the rainfall total.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 contoursEach 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.Part of the BloomWX learn library — beginner-friendly explainers covering every surface of the BloomWX weather dashboard. Open BloomWX to see live data for any U.S. county.