An abrupt pattern change across the West will bring dramatically cooler conditions and chances for accumulating snowfall in the higher elevations.
Published Sep 18, 2023 11:22 AM EDT | Updated Sep 18, 2023 11:22 AM EDT
A pattern change plunging into the northwestern United States this week will spread an early-season potential of snowfall, particularly across the mountain ranges. For some locations, forecasters say that the pattern this week will bring the first snowflakes since last winter.
“A cold storm system sinking down out of western Canada will bring chances for accumulating snow to the highest elevations of the Northwest during the middle of this week,” explained AccuWeather Senior Meteorologist Heather Zehr.
AccuWeather meteorologists say that the best chances of snow will be across the higher terrain of the Cascades, northern areas of the Sierra Nevada range and some of the highest elevations of the northern Rockies. The cool air mass seeping southward from Canada will bring a gradual decline in temperatures into the middle of the week.
“As early as Tuesday night, the zone of low pressure is expected to drop into western Washington, and conditions will turn cold enough to start to snow in the northern Cascade, with snow levels dropping to below 6,000 feet. The risk for snow will then spread south and east into Oregon on Wednesday although snow levels will be slightly higher,” stated Zehr.
By Wednesday, cities in Washington, such as Seattle and Spokane, are expected to drop into the middle to lower 60s F for their daytime highs. Overnight temperatures for Seattle are not expected to vary too much from the lower 50s that have been observed on occasion throughout the month of September. However, conditions in Spokane this week can fall into the 40s overnight, a value so far only observed once earlier this month.
There will be a drastic difference in temperature values at the end of the weekend compared to forecast highs later this week. Many cities, such as Portland, Oregon, and Reno, Nevada, will observe daytime highs dropping anywhere between 20 and 25 degrees Fahrenheit compared to weekend values.
“The core of the cold will mainly grip areas of Washington and Oregon around midweek, with freezing levels expected to fall to around 7,000 or 8,000 feet in some locations during the daytime hours,” explained AccuWeather Senior Meteorologist Adam Douty.
Parts of the Elkhorn Mountains and Eagle Caps in the heart of the Wallowa Mountains can get light accumulations of snow by Tuesday night. Mountain summits such as Sacajawea Peak in the Wallowa Mountains of northeastern Oregon and Borah Peak in central Idaho will be among some of the mountain tops at risk for seeing flakes around midweek, both rising to 9,843 feet and 12,662 feet, respectively.
The pattern this week may cause excitement for avid skiers who are eagerly awaiting for the mountain resorts to open this fall. Typically, ski resorts across the Rocky Mountains and Cascades open sometime between late October and November, depending on the seasonal conditions and location.
For snow enthusiasts in general, the early season shift to cooler conditions and the potential for accumulating snowfall can prove exciting for many in the West hoping to catch a glimpse at a few flakes.
“The most likely time and place for snow is over central and eastern Oregon on Thursday with snow levels falling below 6,000 feet once again, but it can snow to the south into the highest peaks of the northern Sierra with snow levels there dropping to 7,000-9,000 feet,” pointed out Zehr.
Zehr added that with these snow levels, accumulating snow is expected to be above pass level for much of the week although few flakes may reach the passes. Travelers are advised to stay up to date on the latest forecast and monitor sources for roadway conditions throughout the week, especially those planning a route through mountain passes.
By Friday, the storm is expected to travel eastward across Nevada, and conditions will gradually turn warmer. Most locations across the Northwest will notice temperatures returning to typical values for mid- to late September.
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