Multiple times a day, the Storm Prediction Center issues a convective outlook for the United States. These outlooks show the areas at risk for severe thunderstorms for that particular forecast period. The risk for a severe thunderstorms is broken into five categories: Marginal, Slight, Enhanced, Moderate, and High. Each category is signified by a different color on the map and has a basic definition. They are:
- Marginal (dark green): Isolated severe thunderstorms possible
- Slight (yellow): Scattered severe thunderstorms possible
- Enhanced (orange): Numerous severe thunderstorms possible
- Moderate (red): Widespread severe thunderstorms likely
- High (magenta): Widespread severe thunderstorms expected
The National Weather Service defines a severe thunderstorm as measured wind gusts to at least 58 mph, and/or hail to at least one inch in diameter, and/or a tornado. All thunderstorm categories imply lightning and the potential for flooding. Categories are also tied to the probability of a severe weather event within 25 miles of a location.