Major Cold Wave & Potential Snow in the Lowlands

FastCast—Wednesday, Dec. 22 to Saturday, Dec. 25:

On Wednesday, temperatures will reach the upper 40s to low 50s for the last time in 2021. The next system arrives late Tuesday, continuing through Thursday. The main impacts will be rain and mountain snow. Expect 0.5-1.25 inches of rain across Western Washington through Thursday, except less in the Olympic rain shadow. The mountains will receive 8-24 inches of snow through Thursday. Expect 12-18 inches at Snoqualmie Pass, and up to 24 inches at the higher passes and ski areas. Breezy winds gusting 25-35 mph are possible through Friday. Another system with rain and mountain snow arrives on Friday, continuing into Christmas Day. This system’s forecast is tricky, but generally expect precipitation to begin as rain on Christmas Eve, potentially transitioning to mix overnight. Rain or rain/snow mix will likely fall on Christmas, before potentially transitioning to snow late on Christmas as temperatures fall below freezing. Expect highs in the upper 40s-low 50s on Wednesday, then in the low to mid 40s on Thursday and Friday, and then in the upper 30s on Christmas. Lows will be in the mid to upper 30s. Continue reading the full blog below for information on potentially impactful winter weather ahead.

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Around Christmas, a significant pattern change will take place in Western North America. High pressure will build offshore and over interior British Columbia, funneling arctic air into the Pacific Northwest. 

This is shown below on the Euro model’s forecast for temperature anomalies at 5,000 feet on Dec. 30th.

Temperatures 5,000 feet above the surface are expected to be 20-25°C (~60-70°F) below average.

As you would expect, this will fuel a potential for very cold temperatures in the lowlands. Multiple days below freezing, with highs in the 20s to low 30s and lows in the mid teens to mid 20s.

Below is the Euro temperature forecast for Sunday evening.

Think that’s cold? It’s just an appetizer to what’s in the forecast by Tuesday morning.

While these lows in the single digits to low teens may seem extreme, forecast models have been consistently showing very cold temperatures over the past few days, meaning that this is a possibility that needs to be considered. 

Regardless, temperatures in the 20s can cause pipes to burst and can lead to significant problems for people and pets left outside. Stay tuned for more on this situation.

Now for the chances of snow…let’s take a look at accumulated snowfall (not what will necessarily stick to the ground) through Monday morning.

The Euro model (above) shows 1-4 inches of snow in the lowlands and more from Everett northward.

The GFS model (below) shows more snow than the Euro.

The GFS shows 2-8 inches in the lowlands, with more north of Everett. 

A couple things to note about snow…

1. A White Christmas is not looking too likely, with the highest chances of snow being from Christmas night onward.

2. Snow is still quite uncertain (more uncertain than the cold) and will need to be monitored.

Stay tuned for more updates about this evolving situation. Updates can be found on Twitter and on Michael Snyder’s Pacific Northwest Weather Chasers YouTube channel.