DERECHO: What is it? - KMSP-TV

DERECHO: What is it?

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Meteorologist Steve Frazier Meteorologist Steve Frazier

You may be hearing a lot of talk of this massive storm moving across the Midwest this week. Terms like "Land Hurricane" and "Giant tornado" have been tossed around a lot lately. It's definitely not a tornado, yet the damage could be just as bad. It's also not a hurricane but it does have name, "Derecho".

Now I may speak a little Italian, but not much Spanish. "Derecho" is the Spanish word for "Straight ahead" or "Direct", and a straight line wind event is the best phrase to summarize this meteorological event. It's always good to know what you're talking about, so let us first start with the question, "What is a Derecho?"

As thunderstorms develop, they produce a downdraft of rain cooled air ahead of them. This may also be known as a gust front, that gusty cool wind you feel when a storm approaches.

thunderstorm: evolution of a gust front from a thunderstorm

The downdrafts of storms vary in strengths, but in some cases they are strong enough to cause an upward motion of the warm moist air out ahead of the storm. This upward motion of the air can cause a favorable environment for a new storm to form out ahead, and so on, and so on.

Photo

Now, add to the equation, upper level winds moving in the same direction as these storms, and the result could be stronger and stronger wind gusts out ahead of a massive line of storms. These mid-level winds can brought down and add momentum to the line of storms moving across a region, thus the Derecho is born.

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In preparation for this possible wind event the Storm Prediction Center has outlined specific areas with the most favorable chance of wind reaching severe criteria, 58 mph or greater. Below is a map showing where the strongest winds can be expected on Wednesday.

Thunderstorms — damaging enough on their own — may congeal Wednesday night into a derecho.

Derechos have the potential of creating much stronger than that. Below is a picture, pulled from Wikipedia. showing tree damage in our state back in 1999. Notice how all the trees lay in the same direction?

It looks like all the ingredients will come together for this little weather phenomenon to occur this Wednesday through Thursday. A jet stream moving from west to east, warm moist air ahead of the storms, and cool dry air behind them (Minnesota's contribution). In the path are major cities like Chicago, Indianapolis, and Columbus affecting millions of people.  To leave you with more perspective on the power of these wind events, here is a link to video of a Derecho in Ohio back in June of 2012.

http://www.youtube.com/watch?v=p2ns8l5exOg

Frazier

 

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