White ChristmasDec 21, 2017 By Katie Roenigk, Staff Writer
The blanket of snow that fell overnight Wednesday to Thursday should stay on the ground throughout the coming weekend, producing a "white Christmas" effect Monday in the Wind River Basin, forecasters said this week.
"The snow we just got isn't going anywhere," National Weather Service meteorologist Trevor LaVoie said Thursday, explaining, "(It's) going to stay cold."
Temperatures Friday won't get much higher than the mid-20s, he said, and on Saturday an arctic cold front is expected to pass through the region, keeping high temperatures down in the teens.
The forecast has improved over the course of the week, he noted: Earlier predictions showed temperatures dipping into the -20s and -30s.
"That typically happens with an arctic boundary," he said. "But it looks like the trend of really cold temperatures settling in over the area has backed off. (The front) is mainly going to be affecting the northern plains and upper Midwest."
Anticipated cloud cover should keep the weather warmer, too. Though skies were clear Thursday, LaVoie said cloud coverage would increase overnight into Friday and remain through Saturday, when a dusting of snow will add to the current accumulation on the ground.
Overnight cloud cover is especially effective for trapping in the solar radiation collected during the day, LaVoie explained. If there are no clouds at night, he said all of that heat escapes, and temperatures plummet - even without the effect of an arctic front.
"(But) that's not going to happen now," he said. "The skies will stay cloudy. I'm sure people will breathe a sigh of relief - we won't get into the negative 20s or 30s at this point in time."
Instead, he said, low temperatures over the weekend will stay in the single digits, though they may dip below zero Saturday night.
Once the cold front passes, LaVoie said the clouds will lift briefly during the day Sunday before settling back in Sunday afternoon into Monday.
He said temperatures on those days are forecast to reach the low 20s at the highest.
"The cold air that comes in is going to stay trapped," LaVoie said.
By Thursday morning, LaVoie said 4-5 of inches of snow had accumulated in Riverton, with 6-8 inches in Lander and closer to 9 inches in Sinks Canyon.
LaVoie said Lander got more snow due to the impacts of wind during the storm.
"We had two mechanisms that were in play," he said. "We had the surface front that came through early evening to late afternoon (Wednesday), so it brought the northerly winds. ... Then in the upper levels we had southwest wind."
He called it an "overrunning" situation, with the winds from the north hitting the foothills near Lander and riding up the mountains to circulate with the gusts coming in from the southwest.
"Those conditions are conducive for heavier snow to fall," he said. "It's what we call an 'upslope' pattern."