Was Saturday’s wind storm Colorado’s first-ever derecho? ~ The Denver Post

A rare widespread, damaging wind storm took place on Saturday, and it was quite likely Colorado’s first-ever derecho on record.

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Colorado weather is a lot of things, but one thing it’s not: boring.

What appeared to be a fairly typical Colorado afternoon of wind-producing storms Saturday morphed into possibly the most widespread wind-specific thunderstorm event in the state’s recorded history.

Russ Schumacher, Colorado’s state climatologist, made that contention Sunday while pointing to a number of data points.

“In the storm data record from 1955-2018, the most severe wind reports on a single day in Colorado is 30, on May 22, 2006. (Saturday), there were 91.The most significant wind gusts (75 mph or greater) on a single day was 7, on a couple different occasions. (Saturday) there were 17,”  Schumacher said. “I think it’s fair to say we’ve never had such a widespread damaging thunderstorm wind event in Colorado, at least since reliable records have been collected.”

One thing that appears abundantly clear: Saturday’s story was likely Colorado’s first-ever significant derecho on record.

A derecho is a wide and long-lived line of damage-producing severe thunderstorms, but they’re far more common in the eastern half of the country. While individual thunderstorms produce damage all the time in Colorado, it’s rare to get a long, nearly uniform line of damaging storms like the one the Denver area saw Saturday afternoon.

Colorado-based meteorologist Dakota Smith captured a nearly 12-hour satellite and lightning loop showing the powerful line of storms as it raced through Utah, Colorado and eventually moved into Nebraska and the Dakotas on Saturday night.

Dakota Smith@weatherdak

Rare derecho stretching from Utah to the Dakotas today.

A Rocky Mountain special.

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The line raced through Colorado at speeds of 100 mph at times, but it also covered a wide swath of real estate. For example, a severe thunderstorm warning issued by the National Weather Service office in Boulder was the biggest geographical warning that office had ever issued — and it wasn’t even close.

Russ Schumacher@russ_schumacher

Based on @akrherz’s archive, these are the two largest warning polygons issued by @NWSBoulder by quite a margin

View image on TwitterView image on Twitter
That all appears to add up to the definition of a derecho. According to the Storm Prediction Center (SPC), the national governing body for severe weather, a derecho needs to have a swath of wind damage extending at least 250 miles in length, wind gusts that regularly exceed 58 mph, and a few 75 mph wind gusts or higher mixed in as well.

According to Elizabeth Leitman, a meteorologist with the SPC, Saturday’s line of storms more than fit the SPC’s official definition of a derecho. Leitman said the storms produced damage for “at least” 750 miles (three times the official criteria for a derecho), producing wind gusts that fit the criteria along the way as well.

Elizabeth Leitman@WxLiz

I put together some quick info on Saturday’s derecho event. Only two other derechoes in the Great Basin are well noted in literature. I’ve included storm reports for those events, as well as a derecho frequency map for comparison. Pretty remarkable event!

View image on Twitter

In her tweet, Leitman also contends that far northwestern Colorado was clipped by a derecho in 1994, but that’s believed to be the only other derecho to impact the state in recorded history, or at least since reliable weather records began. Saturday’s derecho was unique in the fact that it covered a big geographical chunk of the state, unlike the 1994 event that merely clipped a small sliver of Colorado.

And, of course, getting any sort of a derecho is rare in the much drier western third of the United States. Dr. Sam Ng, a professor of meteorology at Metro State University, showed the climatology of derechos, and specifically how they tend to concentrate in the Midwest.

Sam Ng@DocWX

Indeed they are. Here’s a Derecho Climatology from SPC. Derechos for the High Plains are rare. https://twitter.com/bianchiweather/status/1269489291119308801 

View image on Twitter
Chris Bianchi@BianchiWeather

Today’s Colorado windstorm was likely a derecho- a very rare, prolonged/widespread/strong wind event for the Front Range. https://twitter.com/DocWX/status/1269488789203808258 

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