Explaining SPC categories and what they mean for you

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On Thursday, parts of the Southeast were under yet another High Risk for severe storms. That’s a 5 out of 5 on the severe scale. But who issues these risk categories? And what do those categories exactly mean?

For reference, a severe thunderstorm is defined as a thunderstorm producing one of the following: measured wind gusts of at least 58 miles per hour, hail at least one inch in diameter and/or a tornado. 

Severe thunderstorm outlooks are issued by the Storm Prediction Center, or SPC, located in Norman, Oklahoma. The outlooks highlight areas that have a chance of severe storms and show how high that threat is. The categories are based on the probability that a severe weather event will occur within 25 miles of a given location.

It is important to remember that every thunderstorm has thunder and lightning; those two hazards are not included when classifying a thunderstorm as severe or not. That is why you always need to use caution and head indoors to a safe place when you hear thunder or see lightning.

The lowest category is a Marginal Risk, which is a Category 1. This means isolated severe storms may develop. Not every storm will be severe, but a few stronger storms are possible. The storms should generally be limited in duration and intensity.

A Slight Risk is a Category 2. This means scattered severe thunderstorms are possible with isolated tornadoes, wind and hail all possible hazards. They may be widespread in nature or even short-lived, but isolated intense storms may impact your area.

The Enhanced Risk is a Category 3. This is used when numerous severe thunderstorms are possible. If you are in the Enhanced Risk area, expect more activity with stronger storms in your area. 

The Category 4 is known as a Moderate Risk. This means widespread severe storms are likely with longer-lived storms. The majority of storms will meet severe criteria and be intense. 

And finally, the rare High Risk, or Category 5, is issued when widespread severe storms are expected. This is seen when multiple tornadoes or a destructive derecho is anticipated. The tornadoes could be strong to violent and on the ground for a long time. Damaging wind and large hail could also bring significant damage. 

It is important to know what these risk categories are and what it could mean for you. But remember, no matter the risk issued for central North Carolina, it is a good idea to have your severe weather plan ready to go. 

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