Explain What A Derecho Is To Your Friends

As the Quad Cities, and a huge part of the Midwest, cleans up from Monday's storms we start to look at the news coverage of us.  And the word that keeps popping up in headlines is "Derecho".  No, it's not a name of a storm like a hurricane.  It's the scientific term for what sent 100 mph winds from the Dakota's to Ohio.

Monday's storm traveled 770 miles in just 14 hours taking down trees, power lines, roofs, semi-trailers and grain elevators along the way.  It left over one million people without power.  To put the power of this derecho in perspective, the recent hurricane Isaias that struck Florida and the east coast had sustained winds around 70 mph.  This derecho also had 70 mph winds, with gusts up to 115 mph.  That puts the top speed of this storm at Category 2 hurricane levels.

So what really is a derecho?  Well in simple terms, it's a widespread, long lasting, fast moving line of storms.  The storms can produce tornadoes, flash floods, and of course as we saw yesterday, damaging straight line winds.  This is the most common effect from a derecho.  The best way to see a derecho on radar is when you see a storm moving in a backwards "C" shape.

To talk to friends and sound like you have a meteorology degree, use this from wikipedia:

Squall lines typically "bow out" due to the formation of a mesoscale high pressure system which forms within the stratiform rain area behind the initial convective line. This high pressure area is formed due to strong descending air currents behind the squall line, and could come in the form of a downburst.

The term has been around for a long time.  And, it actually was first used because of a storm in Iowa.

Derecho comes from the Spanish word in adjective form for "straight" (or "direct"), in contrast with a tornado which is a "twisted" wind.^[3] The word was first used in the American Meteorological Journal in 1888 by Gustavus Detlef Hinrichs in a paper describing the phenomenon and based on a significant derecho event that crossed Iowa on 31 July 1877.

What you really need to know is that here in the Quad Cities, we can expect a derecho of some size about once every year.  But this is 2020.  So I'd expect another one in a couple weeks.

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