More Rain & Mountain Snow Ahead

FastCast—Monday, Dec. 20 to Wednesday, Dec. 22:

After a brief break in the weather, even featuring some sun, on Sunday, more rain & mountain snow is ahead to start this week. Expect a chilly and rainy day in the lowlands on Monday, with highs only reaching the upper 30s. Brief rain/snow mix is possible on higher hills on Monday morning, but this is not likely. Precipitation will decrease in coverage north of Seattle. Areas from Seattle south will receive 0.3-1.0 inches of rain on Monday and Tuesday, and the mountains (mainly from Snohomish County south) will receive another 8-18 inches of snow. The next system arrives Tuesday evening, bringing another round of rain (0.25-1.25”) and mountain snow (at least 5-10 inches). Breezy conditions, with gusts up to 30 mph, are expected on Wednesday as well. Expect highs in the low 40s on Tuesday and upper 40s on Wednesday. Continuous, potentially significant cooling is expected toward the end of the week.

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The mountains have been hammered with snow in the past couple weeks. Saturday brought significant snow to the passes yet again, and eventually prompted the simultaneous closure of Snoqualmie and Stevens Passes on Saturday evening. 

In the photo below from Gunner Hicks, taken Saturday afternoon, you can see compact snow & ice on I-90, resulting in heavy traffic.

This scene will likely be repeated in the upcoming days, with more systems bringing snow to the mountains and rain to the lowlands. 

Expect a chilly day Monday, with highs only reaching the upper 30s. Biting north winds from the Fraser River Valley will keep wind chills in the low to mid 30s, except in the low 20s to low 30s in Whatcom and San Juan Counties.

Brief rain/snow mix is possible in the Lowlands early Monday morning, mainly on higher hills, but this doesn’t look like a very likely possibility.

Below is the HRRR forecast for rain through midday Tuesday.

Since precipitation is moving up from the south, a number of forecasts show a sharp cutoff in rain totals between Tacoma and Seattle. The HRRR shows nearly 1 inch in Tacoma, but only 0.2” in Seattle.

The HRRR forecast for snow is similar, showing a sharp cutoff in totals north of Stevens Pass.

Expect 8-18 inches at the passes through midday Tuesday. 1-7 inches of snow are also expected in Eastern Washington, mainly south of Spokane. 

The next system arrives late Tuesday, with another round of rain and mountain snow, though this system will be slightly warmer.

There is a potential for significantly colder air and chances of snow in the lowlands beginning around Christmas. This is still quite uncertain, and details are changing constantly. Stay tuned for further updates!

Western Washington weather updates can be found at local storm chaser/meteorologist Michael Snyder’s YouTube channel, Pacific Northwest Weather Chasers. He has informative briefings and live updates!