Tuesday, April 7, 2015

Undertanding Severe Thunderstorm Risk Categories

In October the Storm Prediction Center implemented two additional severe storm risk categories in their outlooks. I blogged about these changes at the time (Changes to Severe Weather Outlooks), but now that we are in the heart of severe storm season I thought it would be a good idea to mention these changes again. You can read a lot more about the specifics in my October blog post. Recently the National Weather Service office in Kansas City (Pleasant Hill) and the Storm Prediction Center in produced a new graphic that should make understanding the differences between these categories easier. The SPC worked with NWS offices and forecasters, communications experts, social scientists, and the public to come up with the descriptions for the severe thunderstorm risk categories.

First, let's take a look at the Day 2 outlook (for Wednesday) issued earlier today, as it shows both the Marginal and Enhanced categories.

This is the SPC outlook for Wednesday, April 8 made on Tuesday, April 7. The Marginal Risk is in dark green, the Slight Risk in yellow, and the Enhanced Risk in Orange.

How should you interpret the risk for severe thunderstorms in each area? Here's the graphic produced by the NWS.

You can read more about the science and numbers behind the severe storm categories at the Storm Prediction Center web site.

One important thing to remember is that any thunderstorm, severe or not, is potentially dangerous. Lightning is the second leading cause of weather fatalities in the U.S., second only behind floods. Lightning itself is not a criteria for a severe thunderstorm. Don't be lulled into a false sense of security by a lower risk category.

You can read more about the science and numbers behind the severe storm risk categories at the Storm Prediction Center web site.

Also, on April 14 the SPC will add a new Summary section to Public Watch Notification Messages. Per the SPC, "The new Summary section is a general 1-2 sentence statement of the severe weather expected in and close to the watch area. This new section facilitates consistent, forecaster-driven, concise communication for public consumption. The Summary is intended to be useful for a variety of communication needs including web page headlines, social media and multimedia briefings."

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