What are the 5 severe thunderstorm risk categories?

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FARMERSBURG, Ind. (WTWO/WAWV) – We’ve talked about tornadoes, flooding, and lightning but now let’s dive a little deeper into understanding the different categories associated with severe thunderstorm risk. 

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 these thunderstorm categories imply lightning and the potential for flooding. Categories are also tied to the possibility of a severe weather event within 25 miles of your location. 

There are five main categories in understanding severe thunderstorm risk.

The first is marginal (MRGL) and the most common risk issued by the Storm Prediction Center. It means that isolated severe thunderstorms are possible, and they are limited in duration, coverage, and/or intensity.

The second is slight (SLGT) which means scattered severe thunderstorms are possible. Typically, these will be short-lived with isolated intense storms possible.

The third is enhanced (ENH) which means numerous severe storms are possible. Even more persistent widespread ones with a few intense ones are possible.

The fourth is moderate (MDT) which means widespread severe storms are likely. These thunderstorms can be long-lived, widespread, and intense.

The fifth and strongest is high risk (HIGH). This is the least common one issued by the Storm Prediction Center so if this is issued for your area, you need to be on high alert and pay attention to the weather at all times. This level means widespread severe storms are expected. These storms will be long-lived, very widespread and particularly intense. 

The first example included in this package of an outlook issued by the SPC was from last Saturday, March 13th. 21 tornadoes struck areas all across the panhandle of Texas including a large wedge tornado, a rain wrapped tornado, and several smaller brief tornadoes. This was the first moderate risk issued in 2021.

The second example of an outlook was from March 2nd, 2012 that produced 160 tornadoes! Between tornado, wind, and hail reports there were 954 storm reports that day. Our area was under moderate risk and just south east of our viewing area was under high risk. The Henryville Indiana EF4 tornado was one that happened that day and was the closest touchdown to our area.

The last outlook was from 2019 and has all 5 risk categories included on it. Lots of storm reports were also reported that day. 

High risk days are pretty rare. In fact, there were no high-risk days in all of 2020 anywhere in the U.S., the first one in a while was actually Wednesday, and the last high risk for this area was on November 17th, 2013, so more than 7 years ago!

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