Understanding Severe Thunderstorm Risk Categories
The Storm Prediction Center based in Norman, Okla., provides convective outlooks at 5 different times per day to the public. This information describes the potential for severe weather within 25 miles of your location for the contiguous United States. The risk categories are General, Marginal, Slight, Enhanced, Moderate, and High.
General Risk (Level 0)
A light green shaded area means no severe thunderstorms are expected but general thunderstorms could form and produce winds 40 mph or less and/or small hail less than 1” in diameter. A lightning threat exists but not reaching severe wind or hail parameters.
Marginal Risk (Level 1)
A darker green shaded area means isolated severe thunderstorms are possible which could produce wind gusts 40 to 60 mph, hail up to 1” in diameter, and bring a low risk for tornadoes. Storms will be limited in duration, coverage, and/or intensity.
Slight Risk (Level 2)
A yellow shaded area indicates scattered severe thunderstorms will be possible that could contain one or two tornadoes, strong winds that cause damage, and hail near 1” with isolated 2” reports. Storms will be short-lived and/or not widespread, isolated intense storms are still possible though.
Enhanced Risk (Level 3)
An orange shaded area means numerous severe thunderstorms are possible and may produce a few tornadoes, several reports of wind damage, and/or damaging hail 1 to 2” in diameter. Storms are more persistent and/or widespread in this category with a few storms becoming intense.
Moderate Risk (Level 4)
A red shaded area indicated widespread severe thunderstorms are likely and could bring strong tornadoes, widespread wind damage, and/or destructive hail 2” or greater. Storms will be long-lived, widespread, and intense.
High Risk (Level 5)
A pink shaded area is the strongest of the 6 categories and means a very dangerous tornado outbreak or derecho is forecast. Storms will be long-lived, widespread, and very intense.
Just remember, the higher the risk category the more dangerous the weather situation is for a particular day. If you see yourself under one of the categories, it’s best to have a severe weather plan ready in case a watch or warning gets issued.
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Image: A Convective Outlook from March 25, 2021 that depicts all thunderstorm risk categories. Numerous Tornadoes occurred across the Deep South and Tennessee Valley on this day. NOAA/NWS Storm Prediction Center
