The snow blanketing the northern tier is characteristic of a developing La Niña-related weather pattern, which often brings cold, stormy weather to the northern Rockies and northern Plains, while milder-than-average conditions occur elsewhere.
More snow is on the way in many areas, with two more storms in the forecast this week.
Dangerous snow squalls and whiteouts in Iowa
Snow swept over the northern Great Plains and Corn Belt overnight Sunday into Monday, with the wintry weather having a greater impact than anticipated. A trace of snow fell in Omaha, but Harlan, Iowa, about 50 miles northeast, picked up 4.5 inches.
Ankeny, Iowa, just north of Des Moines, had accumulated more than half a foot by early afternoon Monday. A heavy band of snow with rates of one to two inches per hour settled along an east-to-west zone just north of Interstate 80, causing multiple accidents on Interstate 35.
The intensity of the snowfall prompted the National Weather Service to issue a rare snow squall warning for Des Moines and its northern suburbs.
“Serious injuries and deaths may result from people exiting their vehicles during a snow squall,” the Weather Service warned. “Dangerous life-threatening travel” and “rapid [snow] accumulations” were predicted.
It was the first such warning issued by the Des Moines Weather Service office.
The snow was forecast to transition over to rain as it crossed the Illinois border and approached the Windy City.
Minneapolis braces for several inches Tuesday
Farther north, snow is likely to continue to fall. Two to five inches are expected in Minneapolis on Tuesday. If four inches accumulate, that would be the earliest four-inch-plus total on record in the Twin Cities.
The Weather Service has issued a winter weather advisory from 10 a.m. to 10 p.m. Tuesday for the area.
“The first notable accumulating snowfall event of the season is on the way tomorrow for much of the area,” it wrote in its forecast discussion.
Some computer models show the potential for even more than five inches of snow, but some may not accumulate initially because of warm ground temperatures.
The Twin Cities saw their first flakes of the season last Friday, when a wet coating accumulated.
Heavy snow sweeps across Northern U.S.
The storm that socked central Iowa and is pointed at the Twin Cities has its origins in the northern Rockies.
Great Falls, home to roughly 60,000, picked up 13.3 inches over the weekend, just days after temperatures were in the 80s.
“We snowed pretty much continuously through [Monday] morning,” said Paul Nutter, a lead meteorologist at the Weather Service in Great Falls. “The heaviest period was [Sunday]. The storm total now is over 14 inches … that’s going to be pretty unusual for this area.”
Sunday’s total also proved the heaviest calendar-day snowfall on record for the month of October. The city averages only 1.9 inches throughout the month.
Billings saw 9.6 inches out of this latest storm through Sunday night, while flakes were noted in eastern Montana near Glendive. Even Rapid City, S.D., saw a bit of snow. Fargo, N.D., got just over half an inch.
“It is normal for us to have a lot of variability this time of year,” Nutter said.
Cold front helps the fight against wildfires in Colorado
The cold front that has set the stage for snowfall along the northern tier is also responsible for slightly easing fire conditions in the Rockies, where blazes erupted over the weekend.
The Cameron Peak wildfire, burning since August, is the Centennial State’s largest wildfire on record. It has torched more than 200,000 acres so far and is still growing as it rages west of Fort Collins. Other fires, including the blossoming CalWood Fire, have erupted northwest of Boulder, prompted evacuations and destroyed homes.
That same wintry air mass that helped spark wind and snow farther north sagged southwest Saturday, increasing humidity levels and dropping temperatures. Cool weather is less conducive to wildfire spread, since less evaporation occurs, meaning vegetation won’t be quite as dry. However, a temperature inversion related to the incoming colder air, with warmer air aloft and colder air at the surface, caused fog that grounded firefighting flights from reaching the CalWood blaze Sunday.
Highs peaked at 70 degrees Saturday afternoon in Fort Collins. But the winds switched from southeasterly to easterly or northeasterly after sunset, with temperatures falling as relative humidity increased. Lows the next morning bottomed out at freezing, with fog, mist and light snow in the vicinity.
Firefighters captured photos Sunday of flames lapping at snow-dusted logs, a strange scene showing the clashing seasons.
Colorado is in the grips of worsening drought conditions, and dry weather along with unusually hot temperatures have led to an unprecedented spate of large wildfires so late in the year.
More snow to come
Meanwhile, two more episodes of accumulating snow are likely for the northern tier this week. The first will accompany a disturbance ejecting out of the northern Rockies toward midweek, sweeping northeast into the Upper Midwest and northern Great Lakes on Friday.
A strip of snow is likely from Montana through North Dakota and into Minnesota. Accumulating snow could also sneak into northwestern Wisconsin.
Some of the more aggressive models are calling for pockets of eight-plus inches to accumulate, especially across central South Dakota.
Another round of snow is possible in parts of the central and northern Rockies into the High Plains early next week, but specifics remain uncertain.