The Straight Talk about Derechos

Jan 29, 2016


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The derecho is coming! Prepare for the “land hurricane”.

“The Line Storm,” by John Steuart Curry, 1934

On June 11, the National Weather Service (NWS) warned the Midwest and Eastern states that a derecho was coming. Two years ago, most people wouldn’t have known what they were talking about.

After last year’s 700-mile-long super storm, however, Midwesterners were bracing themselves for the worst. Fortunately, this year’s event was a “low-end” event stretching from Iowa to Maryland.

It left Chicago in the dark, spawned tornadoes and spectacular hail, but it was far less damaging and deadly than last year. What most newspapers didn’t report is that there were three lines of storms at the same time: one in the Midwest and Mid-Atlantic and two roaring through the Southeast. They formed one enormous jumble of crummy weather.

On June 1213, the US experienced 3 massive lines of storms! Source NOAA

Technically, a derecho is a “widespread, long-lived storm that is associated with a band of rapidly moving showers or thunderstorms.” It gets its name (Spanish for “straight”) from its powerful, straight blasts of wind that can be as damaging as a tornado.

Typically, tornados do more structural damage, twisting buildings off their foundations; derechos just flatten things. They are notorious for leveling huge areas of trees, in giant “blowdowns”. According to the NWS, the wind damage has to be at least 240 miles long with gusts are at least 58 mph, to qualify as a derecho. This June’s largest storm was 400 miles long with at least one area reporting blasts of 100 mph, spawning an estimated 25 tornadoes as well.

The storms form when cooler air crashes into almost stationary heatwaves. The ones in the Great Plains, called “Serial Derechos”, form on the western edge of the heat. They advance east like a giant line dance. Further north, the Midwestern storms are “Progressive Derechos” and stream over the heat wave like a long deadly train. Along much of the Mississippi and Ohio River Valleys, the storms are almost yearly.

Derechos frequently form around heat waves. Source NOAA

Because they are so huge, derechos frequently get rather odd names: “The Ohio Fireworks Derecho” (1969), “The ‘More Trees Down’ Derecho” (1980), “The Storm of the Century Derecho” (1993) and, more ominously “The People Chaser Derecho” (2001). We were lucky that this year we only had a relatively quiet “low-end” derecho.

Did the derecho affect you? Share your stories!


About This Blog

Are you a weather watcher? Welcome to "Weather Whispers" by James Garriss and until recently, Evelyn Browning Garriss. With expertise and humor, this column covers everything weather—from weather forecasts to WHY extreme weather happens to ways that weather affects your life from farming to your grocery bill. Enjoy weather facts, folklore, and fun!

With heavy hearts, we share the news that historical climatologist and immensely entertaining Almanac contributor Evelyn Browning Garriss passed away in late June 2017. Evelyn shared her lifetime of weather knowledge with Almanac editors and readers, explaining weather phenomena in conversation and expounding on topics in articles for the print edition of The Old Farmer’s Almanac as well as in these blog posts. We were honored to know and work with her as her time allowed, which is to say when she was not giving lectures to, writing articles for, and consulting with scientists, academia, investors, and government agencies around the world. She will be greatly missed by the Almanac staff and readers.

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Because I grew up in Maine,

Because I grew up in Maine, which is frequently on the northern edge of a "heat wave," we have a lot of stories and folklore about "line storms." Fishermen who see a row of "boot-top" clouds (that look like rolled-down fishermen's boots) know to get to a safe harbor or lee shore as fast as possible. My farmer grandpa called them a "squall line" and knew to get the hay wagon under cover, forgetting what hay was left in the field.

I've seen "blowdown" results in Maine forests, whole swathes of trees flattened. The last one that I saw covered an area of roughly 200 acres.

Fantastic stories! Did you

Fantastic stories!

Did you know that this "blowdown" may have created a tsunami?

Fantastic stories! Did you

Fantastic stories!

Did you know that this "blowdown" may have created a tsunami?

Interesting! I've never seen

Interesting! I've never seen one.

I remember the similar one

I remember the similar one that hit michigan big time in 1998. I was out back firing up my generator when I watched a small tornado twist the top out of the oak tree in my back yard. I ran like H*** for the basement. after all my neighbors thanked me for cutting up there trees that were down I had enough fire wood for 3 winters because of that storm. my one neighbors daughter saw a rat tail coming over the lake we live on just before I watched the same one tear the oak out in the back yard we were without power for 2 weeks glad I had the generator. the kids came over to watch the NBA finals at my house we were the only ones with power. I don't think I'll ever forget that storm I watched it come in and blow out. it was the same type of storm that just glanced us like this last one.

Good thing you had that

Good thing you had that generator!

It's great when your memory of a horrible storm has a happy ending -- like enough fire wood for three winters.

It did affect me. I live in

It did affect me. I live in Virginia and this is the 2nd year in a row. Last years however, was much much worse. We were in the dark for a week and can you imagine having no power in the realm of a historic heat wave? We had no air conditioning and indeed, it got so dangerously hot we had to stay at a cooling shelter. This year my power was only out for one night so it wasent too bad. However, trees were uprooted and homes were destroyed. We were fortunate because instead of it being over 100 degrees with suffocating humidity, it was only 80! (making it much easier for the power companies to work outside) we didnt need this anyway... we already had Andrea and flooding to deal with on the east coast

I'm glad this storm wasn't as

I'm glad this storm wasn't as bad as last year's derecho. It sounds as if it was miserable.

Fortunately, Virginia and the East Coast are due for spottier rain that may ease the recent flooding.


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