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Chilly air, rounds of rain and snow on tap for Northwest through weekend

November 01, 2017; 4:39 PM

Snow is ongoing at this time across western Montana thanks to upslope flow across the northern Rockies and a cold front diving southward into the area. This is creating some hazardous travel across the area.

Elsewhere across the Northwest, there is not much going on weather-wise but that will change for the second half of the week and weekend as two storms are expected to bring unsettled weather.

Chilly air is expected to continue to dive southward into the Northwest through the end of the week. A piece of upper-level energy is forecast to dive southward over the coast of British Columbia during this time and will strengthen into an upper-level closed low. This is expected to form a surface area of low pressure just off the coast of Washington and will help bring unsettled weather in the form of rain for some and snow for the Cascades, Bitterroots and northern Rockies and Sierra.

gfs 500 mb nw 11/1/17

An upper-level low will help form a surface low and bring a round of rain and snow Thursday through Friday night to the Northwest. Shown is GFS 500 mb winds, vorticity and heights for Thursday afternoon.

The heaviest snow with the first storm (excluding the Sierra) will occur Thursday and Friday and with chilly air settling in across the region, snow levels are forecast to drop to around 1,500 to 3,000 feet from north to south across the Cascades, Bitterroots and northern Rockies by Friday. This will bring slippery travel to most of the passes.

stormy nw thu-thu night

For the northern Sierra, snow is expected Friday and will continue through the weekend for locations generally above 6,500 feet, although this will fluctuate at times.

A trough in the upper-level winds will remain across the West through the weekend and another piece of energy is expected to round the trough. This will allow for another storm system to form, resulting in more rain and snow Saturday night through Sunday night. With chilly air locked in through the weekend, freezing levels will remain low.

500 mb gfs nw 11/1/17 #2

Rain is expected for coastal areas and the I-5 corridor around Portland and Seattle where temperatures will be around 10 F below average each day and night. Much-needed rain will also fall across portions of California through the weekend.

Total snow through both storms will be a general 1 to 2 feet across the Cascades, Bitterroots, northern Rockies, and Sierra. However, some of the highest locations in the Sierra and northern Rockies could see up to 3 feet of snow.

stormy fri-sun night calif

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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