Timing of snowfall, cooling pavement temperatures created recipe for disaster Thursday on Spokane streets

Above-freezing pavement conditions turned Thursday’s midmorning snow into slush before refreezing that afternoon.

It was that recipe that turned Spokane streets into an ice-skating rink for drivers that day, according to an Inland Northwest Weather Blog post by the National Weather Service in Spokane.

There were 125 crashes reported between noon and 8:30 p.m. Thursday, according to Kirstin Davis, Spokane Public Works Department communications manager. Eighteen of those were injury collisions, said Julie Humphreys, Spokane Police Department spokesperson.

“To me, I think one of the biggest factors was just how cold it got that quickly that evening,” said Steve Bodnar, meteorologist with the NWS in Spokane.

The blog post stated 1 to 3 inches fell in the Spokane area that day, starting just before 10 a.m. and ending at 4 p.m., which is right around sunset.

“There was little to no time to get the roads dry,” Bodnar said.

The roads likely would have been less treacherous had the snow started a few hours earlier, the post stated.

It said temperatures stayed around freezing during the day, but some pavement conditions, like on Interstate 90 on the Perry Street curves in Spokane, were at 34 degrees, turning the recently fallen snow to water or slush on well-traveled roads. But the pavement cooled below freezing around 2:30 p.m., meaning the moisture on the streets quickly froze and caused icy conditions.

Bodnar said a moderate amount of snow started falling around 3 p.m. and helped drive down the pavement temperatures.

Meanwhile, I-90 at Liberty Lake painted a different picture.

The road temperature there remained below freezing for the entire snowfall , so it’s likely there was little or no snow melting, meaning conditions probably weren’t as icy as other parts of the Spokane metro area, the post stated.

More recently, 3 inches of snow fell Saturday in Spokane, according to the NWS.

That snow transitioned to rain in some areas, like downtown Spokane, Saturday afternoon.

Bodnar warned drivers that streets could be icy Sunday and Monday mornings. He said 2 to 3 inches of snow could fall between Sunday night and Monday morning.

“The heaviest activity looks to be south of the Spokane area, but that will move northward late Sunday night and early Monday morning, so we need to be prepared for another snow event coming in Monday for potentially impacting the Monday morning commute,” he said.

Bodnar said a “fairly unsettled weather pattern” this week will bring several opportunities for light snow. Expect temperatures in the 30s and 20s.

Area mountains will receive snow on and off this week as well.

A system late this week, around Christmas Eve and Christmas, has the potential to produce heavy snow in the mountains, so drivers planning to travel through the passes should keep an eye out for that, Bodnar said.

Spokane Public Works Director Marlene Feist said Saturday afternoon that streets crews sanded, de-iced and plowed early Saturday morning and continued maintenance throughout the day.

“They’ve got extra crews on today and planned for overnight,” she said.

The break in snowfall late Saturday morning and early afternoon allowed crews to catch up on plowing, Feist said.

She said the plan for Saturday night was up in the air as of Saturday afternoon because it was unclear if the city would receive rain or snow.

“It’s kind of a wait-and-see moment in terms of what the eventual plan will be,” she said.