Is TSTM the same as severe weather?

No. TSTM means non-severe thunderstorms expected. The next level up (MRGL — Marginal Risk) is the lowest tier that includes any severe-weather expectation. Lightning, brief heavy rain, and gusty wind below severe limit are typical TSTM impacts — but lightning still kills more people per year than tornadoes, so a TSTM forecast is not "fair weather."

What does a TSTM area look like on the SPC outlook?

On the convective outlook map, TSTM areas are shaded a light tan or yellow-green and labeled "GENERAL THUNDERSTORMS." They cover a much larger area than the categorical severe risks above them and represent the daily background of ordinary convection across the country.

How often does SPC issue TSTM?

TSTM is issued daily over hundreds of thousands of square miles east of the Rockies during the warm season. It is by far the most common SPC outlook category and represents typical pop-up summertime convection.

What Does TSTM Mean in Weather? — SPC General Thunderstorm

What Does TSTM Mean in Weather? — SPC General ThunderstormTSTM (General Thunderstorm) is the lowest category on the SPC convective outlook. Ordinary non-severe storms expected, severe probability below 5%. Definition, examples, and where TSTM sits relative to MRGL and the full SPC categorical scale.TSTM is the SPC abbreviation for General Thunderstorm — the lowest category on the Storm Prediction Center's convective outlook, used where ordinary (non-severe) thunderstorms are expected. Severe-weather probability is below 5%. A TSTM area does not mean storms will be quiet; it means SPC does not expect them to reach severe criteria (1″ hail, 58 mph wind, or a tornado).Where TSTM sits in the SPC scaleFrom lowest to highest: TSTM (general thunderstorm) → MRGL (Marginal, level 1) → SLGT (Slight, level 2) → ENH (Enhanced, level 3) → MDT (Moderate, level 4) → HIGH (level 5). TSTM is the baseline tier added in the 2014 scale revision — before that, sub-MRGL convection had no formal label.Expected impactsLightning, brief heavy rain, gusty wind below the 58 mph severe threshold, small-pea hail at most. Lightning still kills more people per year than tornadoes, so a TSTM forecast is not "fair weather" — outdoor events should still have a lightning plan.What TSTM triggers operationallyFor most operations, TSTM is a "stay aware" tier rather than an action tier. Spotter networks stay on standby. Outdoor-event planners watch radar. Aviation plans for routine convective avoidance. The next level up (MRGL) is typically the threshold for active spotter activation in most regions.How common is TSTM?TSTM is by far the most-issued category — daily across hundreds of thousands of square miles east of the Rockies during the warm season. It represents the daily background of ordinary convection: the pop-up summer storm that produces a brief lightning show and a half-inch of rain.See the full SPC convective outlook guide for the complete scale, probabilistic tornado / hail / wind contours, and the supercell / MCS / QLCS glossary.

Frequently asked questions

What does TSTM mean in weather?: TSTM is the SPC abbreviation for General Thunderstorm — the lowest category on the convective outlook, used where ordinary (non-severe) thunderstorms are expected. Severe-weather probability is below 5%. A TSTM area does not mean storms will be quiet; it means SPC does not expect them to reach severe criteria (1″ hail, 58 mph wind, or a tornado).
Is TSTM the same as severe weather?: No. TSTM means non-severe thunderstorms expected. The next level up (MRGL — Marginal Risk) is the lowest tier that includes any severe-weather expectation. Lightning, brief heavy rain, and gusty wind below severe limit are typical TSTM impacts — but lightning still kills more people per year than tornadoes, so a TSTM forecast is not "fair weather."
What does a TSTM area look like on the SPC outlook?: On the convective outlook map, TSTM areas are shaded a light tan or yellow-green and labeled "GENERAL THUNDERSTORMS." They cover a much larger area than the categorical severe risks above them and represent the daily background of ordinary convection across the country.
How often does SPC issue TSTM?: TSTM is issued daily over hundreds of thousands of square miles east of the Rockies during the warm season. It is by far the most common SPC outlook category and represents typical pop-up summertime convection.
What does TSTM trigger operationally?: For most operations, TSTM is a "stay aware" tier rather than an action tier. Spotter networks stay on standby; outdoor-event planners watch radar; aviation plans for routine convective avoidance. The next level up (MRGL) is typically the threshold for active spotter activation in most regions.

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