Storm Prediction Center Convective Outlooks: what does each category mean?

Weather Blog

INDIANAPOLIS – The Storm Prediction Center, located in Norman, Oklahoma, is part of the National Oceanic and Atmospheric Administration of the United States Department of Commerce. Also known as SPC, they put out national forecasts depicting the severe thunderstorm risk in specific areas. These forecasts are called Convective Outlooks. What do they mean? What should you do? Let’s break down each category.

*THIS IS NOT A CURRENT FORECAST*

Generic Thunderstorms

This category has no “level”. This depicts sub-severe thunderstorms. Lightning and heavy rain are possible in these storms. Flash flooding could also occur in those heavier pockets of rain.

Level 1 – Marginal Risk

A marginal risk for severe storms is the lowest risk. Severe storms tend to be isolated, short-lived, with limited intensity. This means one or two storms could become strong to severe in the highlighted area. Damaging wind gusts from 40-60 mph, hail up to the size of quarters, and an isolated tornado are all possible in any severe storms in a marginal risk area. SPC says storms in a marginal risk area are, “limited in duration and/or coverage and/or intensity”.

Credit: Joe Brunton

Level 2 – Slight Risk

A slight risk for severe storms is a level 2 out of 5. Severe storms in an area highlighted by a slight risk tend to be scattered, short-lived, and isolated in intensity. This means a few storms could become strong to severe in a slight risk area. Damaging winds, large hail, and 1-2 tornadoes are all possible. SPC says storms in a slight risk area are, “short-lived and/or not widespread and isolated intense storms are possible”.

Level 3 – Enhanced Risk

An enhanced risk for severe storms is a level 3 out of 5. Severe storms are numerous and persistent. Depending on the environment, damaging winds up to 70 mph, large hail, and a few tornadoes are all possible in this risk. SPC says storms in an enhanced risk area are, “more persistent and/or widespread with a few intense storms”.

Credit: Rebecca Elkins

Level 4 – Moderate Risk

A moderate risk for severe storms is a level 4 out of 5. Severe storms are widespread, long-lived, and intense. Strong tornadoes, widespread wind damage, and large hail are all possibilities in this risk category. SPC says storms in a moderate risk area are, “Long-lived, widespread, and intense. Widespread severe storms are likely”.

Level 5 – High

A high risk for severe storms is a level 5 out of 5. This is a category that rarely gets issued. Severe storms in this risk are widespread, long-lived, and very intense. Tornado outbreaks and significant wind damage are likely in this risk. SPC says, “Widespread severe storms are expected. Long-lived, very widespread, and particularly intense storms are possible”.

What should you do when any of these are highlighted in your area?

  • Know the difference between a watch and a warning
  • Have a plan of action ready
  • Stay informed with the latest forecast

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