A big change in the weather will change summerlike conditions to winter across parts of the Northwest and Rockies.
Temperatures were well above normal in the Northwest most of the summer and that trend continued into early fall. October began with temperatures more typical of July or August in the northern Rockies. The high in Helena, Montana, soared to 84 degrees Tuesday, surpassing the daily record high of 81 degrees set in 1958. Helena’s average high for Oct. 5 is 64 degrees.
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Over the next few days, temperatures will gradually cool down. Cooler air already arrived in the Northwest on Tuesday in the wake of a cold front. Seattle’s high reached only 55 degrees, which is 10 degrees below average.
As the front moves farther inland, many locations in these regions that were in the 80s Tuesday only reached the 60s and 70s on Wednesday. By Thursday, highs will struggle to escape the 50s in some places due to the cooler air, as well as overcast skies and precipitation.
“A storm will begin to cool things down across the northern Rockies on Thursday and Friday, with areas from northern Nevada into Montana, Wyoming and Idaho getting some rainfall,” according to a forecast by AccuWeather meteorologist Rob Richards.
Outside of the highest mountain peaks, temperatures will be too warm to support accumulating snowfall the next couple of days. However, a second cold front with much colder air behind it will arrive by this weekend, followed by another next week.
“This will cause temperatures to fall further and set the stage for a more impressive ripple in the jet stream to usher colder conditions into the Rockies,” Richards added.
A bit of snow may fall on Sunday in the Cascades of Washington and Oregon.
By Monday and Tuesday, a dip in the jet stream will become very pronounced across the Southwest. Much colder air combined with a stalling storm may lead to significant snowfall in parts of the West.
“A storm will blossom and produce windy conditions with snow across most of the northern Rockies, leading to travel disruptions due to the season’s first snowfall of consequence across this part of the country,” Richards said.
While travel could be hazardous as low as 4,000 feet in Montana, affecting locations such as Bozeman and Helena, snow levels will not dip as low farther to the south. However, with snow levels of 5,000 to 5,500 feet in Wyoming, Casper and Riverton could be in line for their first accumulating snow of the season.
Even farther to the south, accumulating snow is not expected in major cities such as Salt Lake City and Denver, but wet snow or a snow-rain mix is possible. At an elevation of 7,000 feet, Flagstaff, Arizona, may also be in line for its first snowflakes of the season, with minor accumulation possible.
It’s too early to accurately predict snow amounts, but any snow that does fall in the West will begin to melt later next week as temperatures warm up.
Also, the National Weather Service is calling for winter weather in the Sierra Nevada. According to a special weather statement issued by the NWS office in Reno, Nevada, confidence is increasing in the chances for high-elevation snow showers Thursday night into Friday. “Several inches of snow will be possible for higher elevations in the Sierra,” according to the statement.
The same cold front heading through the Rockies next week will also impact the Sierra Nevada, with snow levels possibly falling to the valley floors Monday into Tuesday.
Major lanes of concern
• Interstate 80 from Reno to Truckee, California.
• Interstate 80 from Cheyenne to Elk Mountain, Wyoming.
• Interstate 25 from north of Denver to Cheyenne.
• Interstate 15 from north of Salt Lake City to Helena, Montana.
• Interstate 90 from Helena to east of Coeur d’Alene, Idaho.
Click here for more FreightWaves articles by Nick Austin.
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