AccuWeather's Bernie Rayno explains what a derecho is.
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00:00In today's WeatherWise segment, we're going to talk about deratios.
00:08WeatherWise segment, where you take something complicated and make it easy to understand.
00:12Let's give you an easy definition of a deratio.
00:14What is it?
00:15It's a widespread, long-lived windstorm, usually with a fast-moving area of thunderstorms.
00:21They typically move between 40 and 50 miles per hour.
00:24It's all about the straight-line wind damage, all right?
00:27You can get isolated tornadoes, but it's mostly wind, and the wind damage has to be a continuous area
00:34where you have winds of at least 58 miles per hour for at least 400 miles in length, 60 miles in width.
00:46That is what a deratio is.
00:48Now, what happened yesterday?
00:49First, take a look at high temperatures yesterday, because how deratios are usually formed,
00:54they're formed what I call thermally by a lot of heat and humidity,
00:58and they usually occur on the northern edge of the heat and humidity.
01:01Well, look at the heat and humidity here, building across the southeast, right across Indiana and Pennsylvania.
01:07Now, look where temperatures are in the 80s.
01:08Look where in their 70s, all right?
01:10Watch where the deratio formed yesterday from the storm reports.
01:14There it is, starting in Indiana.
01:16And this is typically what you see as well.
01:18It fans out as it moves to the east-northeast before eventually weakening.
01:25Now, how long was this?
01:27Ari and I crunched the numbers here.
01:29It started in Martinsville, Indiana at 1138.
01:32It ended in Tunkhannock.
01:33I think that's in Wyoming County in Pennsylvania.
01:35So it was well over 500 miles.
01:38And when you look at historically, when did the ratios usually start to occur?
01:44They usually begin in May, June and July.
01:47And here we are in late April.
01:50And now you know.
01:52AccuWeather Early continues after this.