Colder Air Bringing Lowland Snow Potential and Heavy Mountain Snow

FastCast—Saturday, Dec. 4 to Monday, Dec. 6:

After days of above normal temperatures, much colder air has set in. Temperatures are much colder, with highs in the low 40s and lows in the low to mid 30s. The mountains will begin to build a good snowpack, with snow totals of 12-24 inches at the passes through Monday. In the Lowlands, there are 2 chances of wintry mix or snow. These chances are Saturday morning and Sunday night to Monday morning. The highest potential for accumulating snow will be in Whatcom County, where up to 2 inches are possible by Saturday morning, mainly on grassy and non-road surfaces. The Cascade Foothills, Northern Olympic Peninsula, Kitsap Peninsula, and Skagit County have a chance of getting a dusting on Saturday morning. For the rest of the lowlands, a rain/snow mix is possible during periods of heavier rain on Saturday morning. Saturday will be wet, with 0.4-0.75 inches of rain expected. A dry and chilly day is expected on Sunday, and stay tuned for more information about the next snow chance!

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The first lowland snow potential is upon us! Much colder air has set in, and temperatures will only reach the low 40s through Monday. There are multiple chances of lowland snow, and the mountains will begin to build a good snowpack, with multiple feet of snow expected through next week.

A weak system will approach the coast from the northwest on Saturday. This system will move through as temperatures are somewhat cold, producing a very marginal chance of snow on Saturday morning (outside of the Lowlands). Rain is expected through the day as well.

Below is the high-resolution NAM model forecast through late Saturday morning from Pivotal Weather.

This forecast shows a dusting of snow in the foothills and Skagit County. The NAM forecasts a trace to 3 inches of snow in Whatcom County and 0.25-2 inches along the Strait of Juan de Fuca (from Port Angeles westward) and in the San Juan Islands.

As always, we can’t just look at one forecast. Below is the HRRR (high resolution rapid refresh) model, also through late Saturday morning.

The HRRR keeps temperatures a bit colder, and forecasts snow from around the King/Snohomish County line northward. While possible, this scenario is not likely. 

Regardless of lowland snow, it will rain on Saturday. It’ll be a classic “cold rain”, as temperatures won’t go above the low 40s. Below is the HRRR forecast for rain through 12 AM Saturday.

Expect 0.3-0.75 inches around the region. Keep in mind that all this will be snow in the mountains. Expect up to 12 inches of snow at the passes on Saturday. Additionally, at times of heavier precipitation on Saturday morning, a rain/snow mix is possible in the Lowlands, especially on higher hills.

A mostly dry (and chilly) day is expected on Sunday, before another potential chance of lowland snow from Sunday night to Monday morning. This chance is also very marginal and will need to be monitored. Stay tuned for an update Sunday night!