A 78 mph wind gust was measured at Denver International Airport as the storm roared through and winds topped 100 mph in the high terrain to its west.
After forming in southern Utah, the storm complex charged ahead at forward speeds up to 100 mph through parts of Colorado, Wyoming and Nebraska, covering 750 miles in 12 hours before reaching the Dakotas.
According to meteorologists at the National Weather Service SPC, it was among the strongest U.S. derechos in recent memory, considered even more remarkable for happening in a part of the country that rarely experiences such storms.
Elizabeth Leitman, a meteorologist at the SPC who analyzed the event, concluded that Saturday’s derecho was “exceedingly rare” due to both its location and intensity. She created a set of summary graphics which SPC shared on Twitter:
Leitman’s research concluded that only two other “well-documented” derechos had taken place in the western U.S. in recorded history: a May 1994 event and another in June 2002. Saturday’s derecho likely moved through areas that had never experienced such an event since accurate weather records began, specifically in parts of Colorado, Utah and Wyoming.
While damaging winds often occur from scattered individual storms during the spring and summer across the West, it's highly unusual to get a huge continuous line of wind damage-producing storms like Saturday's across the Rocky Mountains. The mountains' topography often act to tear apart lines of storms, and an overall much drier climate across the Rockies makes it more difficult to create big lines of severe storms to begin with.
According to the Storm Prediction’s Center official definition, a derecho requires a line of wind-producing storms that spans at least 250 miles, while regularly producing 58 mph winds and a scattering of 75 mph gusts or above. The event typically will also typically last at least a few hours, and the line itself will also usually stretch at least 60 miles.
Saturday's derecho easily met all of those criteria, and then some.
According to Storm Prediction Center data, Saturday’s derecho produced “the most significant wind gust reports in a day” on record for the entire U.S., a reference to the number of 75 mph or greater gusts recorded.
Forty-four separate wind gusts of 75 mph or greater were clocked, including an 110 mph gust at the top of the Winter Park Ski Resort in Colorado. Gusts topping 80 and even 90 mph dotted the map north into Nebraska and the Dakotas later into Saturday evening.
More wind gusts over 75 mph occurred Saturday than during the destructive June 29, 2012 Mid-Atlantic derecho that hammered the Washington area.
A potent area of low pressure spinning through Montana was the primary catalyst for Saturday’s powerful wall of wind. South of the low pressure zone, a strong area of high pressure anchored over the south-central United States (aided in part by sinking air tied to Tropical Storm Cristobal). This created a large different in pressure or gradient over a small distance, setting up exceptionally blustery conditions before the storms had even formed.
The storms developing along a cold front surging eastward, tapping into ample energy from the southerly transport of warm winds ahead of it.
Saturday’s storms, which persisted for nearly 12 hours, ultimately led to over 100,000 power outages across Colorado at one point on Saturday, in addition to thousands more to the north in several other states. As of early Monday morning, over 6,000 customers remained without power in Colorado and Utah.
After a thorough analysis of historical data, Colorado state climatologist Russ Schumacher concluded that Saturday’s derecho stood in a league of its own.
“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,” Schumacher said.
Chris Bianchi is a freelance writer and on-camera meteorologist for Weather Nation.