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Cedar Rapids, Iowa 52401
Dec. 15 storms across Iowa, Midwest classified as derecho
O'FALLON, Mo. — A line of severe thunderstorms and tornadoes that swept across the north-central United States last week was the result of a “serial derecho” — the first on record in December, officials with the National Weather Service said Monday.
At least 45 tornadoes have been confirmed in the Dec. 15 storms that crossed the Great Plains and Midwest amid unseasonably warm temperatures, said Bill Bunting, chief of forecast operations at the weather service's Storm Prediction Center. Iowa, Nebraska and Minnesota took the brunt of the damage.
The Gazette reported on Monday that the forecasts were considered to be consistent a derecho, although it would be up to the Storm Prediction Center to call it. But it was far less than the Aug. 10 2020, that struck Iowa — particular Cedar Rapids — with winds that are estimated to reach close to 140 mph.
Bunting said at least 12 of the tornadoes were rated EF2. Many of the thunderstorms also carried winds of up to 80 mph. Five deaths were blamed on the weather.
Bunting said that normally in December, air from the Gulf of Mexico has cooled, and colder air is present in the Upper Midwest — factors that reduce the risk of severe thunderstorms and tornadoes.
But this year, “we haven’t had much of a winter,” he said.
“So you had a very strong storm system with really somewhat unprecedented access to very warm, humid air that flows northward, and those are the ingredients that you look for for severe thunderstorms," Bunting said. "The result was quite remarkable for December.”
Here is what the weather service has confirmed in Iowa so far:
- An EF1 cut a 4.56-mile in Sergeant Bluff about 4:20 to 4:24 p.m. in Woodbury County.
- An EF2 tornado cut a 2.4-mile path through Pottawattamie County, around McClelland at 4:24 to 4:27 p.m.
- An EF2 cut a 5.48-mile path at 4:26 to 4:32 p.m. in Lawton in Woodbury County.
- Another EF2 struck Pottawattamie County near Neola, cutting a 6.7- mile path, at 4:31 to 4:36 p.m.
- An EF2 cut a 26.1-mile path through Audubon and Cass counties, near Atlantic, from 4:50 to 5:08 p.m.
- An EF1 cut a 6.7-mile path, near Aurelia in Cherokee County, about 4:59 to 5:04 p.m.
- A tornado of unknown strength cut an 18.8-mile path through Carroll and Sac counties, near Lake View, at 5:13 to 5:27 p.m.
- An EF2 cut a 24-mile path through Guthrie and Greene counties, near Bayard, from 5:17 to 5:31 p.m.
- Another EF2 also struck Guthrie and Greene counties, for 17.4 miles near Bagley, from 5:21 to 5:34 p.m.
- An EF1 tornado cut a 14-mile path near Grand Junction in Greene County, near 5:28 to 5:38 p.m.
- An tornado of unknown strength cut a path of 18-miles near Somers and Barnum in Calhoun and Webster counties, about 5:39 to 5:54 p.m.
- An EF2 tornado (preliminary) cut a 4-mile path through Dana in Greene County, from 5:42 to 5:47 p.m.
- An EF2 cut a 26.7-mile path through Greene and Webster counties, near Harcourt and Duncombe, from 5:43 to 6:01 p.m.
- An EF2 cut a 18.4-mile path through Stratford in Hamilton County, at 5:53 to 6:06 p.m.
- An EF2 cut a 28-mile path near Belmond and Meservey in Wright and Cerro Gordo county around 6:21 to 6:40 p.m.
- An EF2 cut a 15.5-mile path through eastern Franklin County at about 6:36 to 6:47 p.m.
- An EF1 hit Floyd County near Marble Rock, cutting an 8.2-mile path at 6:56 to 7:01 p.m.
- An EF1 with winds of 110 mph struck Floyd County around Rudd, carving a path for less than a mile at 6:58 to 7 p.m.
- An EFO with winds of 85 mph struck Chickasaw County around Elma, carving a 5.4-mile path at 7:17 to 7:22 p.m.
- An EF0 also struck Howard County near Maple Leaf, cutting a 6.9-mile path at 7:24 to 7:29 p.m.
- And another EF0 hit Howard County, this time near Schley, carving a 4.5-mile path at 7:29 to 7:32 p.m.
A derecho is often described as an inland hurricane. But it has no eye and its winds come across in a line. The similarity is in the damage, which is likely to spread over a wide area, unlike a tornado where the damage is more spotty.
The weather service said a wind damage swath extending more than 240 miles with wind gusts of at least 58 mph along most of its length can be classified as a derecho.
A derecho was also declared in August 2020 when storms packing 100 mph winds lasted several hours and caused damage from eastern Nebraska, across Iowa and into parts of Wisconsin and Illinois. There was a difference: The August 2020 storm was a “progressive derecho,” while last week's was a “serial derecho.”
The weather service said a progressive derecho is fueled by a hot and moist environment with relatively strong winds aloft. Serial derechos are produced by storms with strong winds that bow outward, the service said. They sweep across an area both long and wide, driven by the presence of very strong winds in the atmosphere.
FILE- A tornado approaches Interstate 80 near Atlantic, Iowa, as a semi truck rolls eastward on Wednesday, Dec. 15, 2021. The National Weather Service has declared the series of thunderstorms and tornadoes that swept across the Great Plains and Upper Midwest on Dec. 15 as a serial derecho, a rare event featuring a very lengthy and wide line of storms. The service said it was the first serial derecho in December in the U.S. (Bryon Houlgrave/ Des Moines Register via AP)
FILE- Wind fueled fires burns in a pasture which was part of a fire that burned and stretched across Ellis, Russell, Osborne and Rooks counties, Dec. 16, 2021, near Natoma, Kan. The National Weather Service has declared the series of thunderstorms and tornadoes that swept across the Great Plains and upper Midwest on Dec. 15 as a serial derecho, a rare event featuring a very lengthy and wide line of storms. The service said it was the first-ever serial derecho in December in the U.S. (AP Photo/Charlie Riedel)
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