At least 180,000 remained in the dark early Thursday in Washington state, Oregon, Idaho and Montana, according to PowerOutage.us, a number that will likely grow as the strong gusts expand east.
Multiple gusts over 107 mph were measured in Alta, Utah, a mountain resort town southeast of Salt Lake City in the Wasatch Range. Mount Sentinel in Montana gusted to 125 mph. But perhaps the most remarkable measurement came from Laramie, Wyo. — a flat area removed from any mountains — where a gust to 105 mph occurred at 1:18 p.m. Wednesday.
A litany of scattered to widespread wind gusts between 80 to 95 mph buffeted Wyoming and Montana. Gusts in Billings, Mont., hit 69 mph, as they did in Bozeman, while Great Falls saw a gust of 76 mph and Helena a gust to 80 mph. A number of locations in Montana reported January record wind speeds.
At the National Weather Service office in Great Falls, a metal silo could be seen rolling through a field adjacent to I-15.
“Usually the Rocky Mountain Front can be counted on to always get the strongest winds in our area,” said Christian Cassell, a National Weather Service meteorologist at the Great Falls office. “This was a bit more of an unusual storm. The wind impacts were a little more widespread.”
He said the strongest winds began Wednesday morning after a warm front slipped through, with sunshine heating the air enough to rise and tap into powerful winds associated with a low-level jet stream. This current of swiftly moving air about 10,000 feet above the ground provided momentum that was dragged all the way down to the surface.
“We basically brought the jet stream down to the surface in a lot of Montana,” said Cassell.
Also a key factor was a significant air pressure gradient, or change of air pressure with distance. A strong high-pressure system to the west over Idaho and the Columbia River Basin squared off with a weak low over southern Manitoba. Since air moves from high pressure to low pressure, it slid east quickly, ramping up in speed as it blasted through the northern United States and taking on a northerly component due to the Coriolis force.
The strength of wind is proportional to how steep that air pressure change with distance is. It’s just like sledding — you’ll zip downhill faster when the hill is at a steeper slope.
The system shifted east late Wednesday, bringing 65-to-80 mph gusts to western parts of the Dakotas and Nebraska.
In Glasgow, Montana, the local National Weather Service office struggled to release its Wednesday afternoon weather balloon in 67 mph winds. The first balloon popped, with delicate instruments smacking the ground twice during the second attempted launch. The latter effort proved successful.
Glasgow later saw a wind gust to 79 mph, just 3 mph shy of the record set during a line of severe thunderstorms on July 3, 2000. The difference, though, between a severe thunderstorm event and this windstorm was the duration of strong winds. Thunderstorms tend to bring brief periods of high winds, whereas this windstorm lasted several hours.
“Last February we had a pretty remarkable windstorm across central Montana,” said Cassell. “In Great Falls it felt like the damage to that one was a bit more significant … but [it] was a bit more localized to central Montana. This one was just so widespread. It went into Canada, all of Montana and even south into Wyoming.”
In Saskatchewan, vehicles were stranded where the strong winds overlapped with snowfall. Blizzard warnings were issued by Environment Canada for much of Saskatchewan and Manitoba, along with freezing rain warnings for parts of Manitoba.
Elsewhere, a gust of 99 was measured in Glen Haven, Colo., about 10 miles southwest of Fort Collins, while Crisman, only five miles west-northwest of Boulder, gusted to 94 mph. Breckenridge, a popular ski destination, reported a gust to 106 mph.
Truckers were urged to stay off I-76 in Colorado, while I-80 was closed for a time between Cheyenne and Rawlins, Wyo. Cheyenne, located in a flat area, reported a gust of 89 mph shortly after 8 p.m.
Meanwhile, the same storm system behind the winds is unleashing blizzard conditions in parts of the Corn Belt, northern Plains and Upper Midwest. A blizzard warning is in effect east of the James Valley in South Dakota, including Watertown and Sioux Falls, as well as in most of western Iowa and southwest Minnesota. Des Moines and Sioux City are both included in the blizzard warning, while Minneapolis is encompassed within a winter weather advisory.
After some initial light snow showers, the greatest snowfall is expected to occur late Thursday evening into Friday morning. A broad 3 to 5 inches will blanket most of Iowa, Minnesota, Wisconsin and western parts of Michigan’s Upper Peninsula. Amounts topping half a foot and locally flirting with 10 inches are possible in north-central Iowa and southeastern Minnesota.
The storm system, which also brought exceptional precipitation to Oregon and Washington state after steering an atmospheric river into the Pacific Northwest, will push all the way to the East Coast by Friday night. Parts of the East Coast are expecting showers along its cold front to kick off the holiday weekend, but fortunately, the winds in this storm system will have slackened by then.