Potent, quick-hitting storm to set its sights on Northwest

 By Mary Gilbert, AccuWeather meteorologist

Updated Nov. 30, 2020 3:26 AM

The wettest period of the year is well underway for the northwestern United States as another quick-hitting storm system will once again look to dump rain and mountain snow across the area early this week.

On Saturday, a small disturbance brought a few rain showers and high elevation snow showers to portions of the Northwest through Saturday afternoon. As this system exited the area late Saturday, dry conditions began to overspread the region.

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While a seasonable late-November day unfolded across the Northwest on Sunday with normal to just-above normal temperatures, the next storm system to take aim at the region took shape just off the coast of British Columbia, Canada.

This more robust storm system for the Northwest will arrive in the area overnight Sunday as rain begins across northwestern Washington. Late Sunday night, a cold front associated with this storm system will stretch from Washington to Northern California, paralleling the coast. This cold front will push east early Monday morning and spread rain across western Washington, western Oregon and the western coast of Northern California. Steady rain will continue to fall in these areas through the afternoon hours.

Generally the rain that falls overnight Sunday through Monday will be steady, but not heavy in nature as this system jogs quickly across the Northwest. Where the most persistent rain falls across western Washington and northwestern Oregon, rainfall totals on the order of 0.50-1.00 inch are likely. This amount of rain is unlikely to trigger any widespread flash flooding concerns, but a few spots may experience some ponding on roadways.

As rain falls across western portions of the region, snow will target the higher-elevation areas. Snow will blanket portions of the Cascades from Monday morning into Monday night as the system comes ashore and pushes east. Even the northern Rockies will get in on the action as the system pushes eastward, with snow expected to fall Monday afternoon through Monday night across portions of Idaho and Montana.

Snow levels will fall throughout the day Monday across the region and ultimately bottom out around 3,000 to 4,000 feet. Accumulating snow is likely to blanket some of the higher mountain passes and make travel difficult or even impossible for a time on Monday. Accumulating snow can even cause issues for travelers attempting to traverse Stevens Pass on US 2 or Snoqualmie Pass on Interstate 90.

A general 1-3 inches of snow is likely to fall for areas above that 3,000- to 4,000-foot elevation mark, while 6-12 inches will be likely for the highest elevations.

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In addition to rain and snow, gusty winds will also be a factor for some across the region into Monday.

"As the storm system moves onshore, winds will turn gusty across the Pacific Northwest. Coastal areas could experience gusts past 40 mph, with widespread 25- to 35-mph gusts farther inland," AccuWeather Meteorologist Renee Duff said.

"Despite this not being a significant wind event for the area, people should be mindful that such winds can knock over lawn furniture or other loose items outdoors, so measures may need to be taken to secure such items," Duff added.

As the storm system exits the Northwest on Monday night, high pressure will quickly build into the region in its wake. This high pressure will act to keep the northwestern United States dry and seasonable through at least the middle of next week.

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