Lowland Snow Potential on Monday & Tuesday

No FastCast today...keep reading below for a look at the active weather coming up for Monday and Tuesday.

A weather system will move through Western Washington on Monday, with 0.2-0.4" of rain and significant mountain snow, followed by Convergence Zone bands that could produce snow due to cold air aloft. In the system's wake, expect colder air to arrive, dropping temperatures, and allowing a weak system on late Monday to early Tuesday to bring potential snow showers. There is also a slight chance of thunderstorms around the area on Monday, due to instability following Monday's system. Monday will also be windy, with gusts 25-35 mph around the lowlands and 45-55 mph on the coast and around the Strait of Juan de Fuca.

There are 2 windows for potential lowland snow:

1. Convergence Zone bands from Monday afternoon to Monday night

2. Convergence Zone bands/scattered snow showers on Tuesday

First, the European model forecast for total snow through Tuesday evening.

The European model shows a dusting to 0.5 inches of snow for most of the lowlands, with up to 1 inch near the foothills. Areas from Olympia south through the Willamette Valley could get up to 1.5 inches of snow.

Additionally, expect 15-24 inches at the passes, with travel delays possible. The Oregon Coast Range may receive 2-6 inches, so some coastal highways could have travel delays as well.

Next, let's take a look at the high-resolution NAM forecast through Tuesday evening.

This forecast shows much spottier snow, with a dusting to 1" of snow from Shoreline north to Arlington, on the northern Kitsap Peninsula, in the foothills, potentially south of Tacoma, on the Central Coast, and from Chehalis south into the Willamette Valley.

The NAM agrees with the Euro in the mountains, showing 15-24 inches at the passes and 2-10 inches in the Coast Range.

Next, the HRRR high-resolution forecast...which has a shorter range, only through Tuesday morning.

This forecast is a bit more complex. The HRRR brings significantly more snow for areas on the coast and from Olympia southward. If this forecast verified, expect a dusting to 1" of snow from Everett southward (isolated up to 2" for the foothills). Meanwhile, the Washington Coast will get 0.5-3", and areas from Olympia southward through the Willamette Valley will get 1-3". WA's coast mountains could get 4-8", and Oregon's Coast Range would get 3-15". 

The agreement continues for the passes, with 15-24 inches likely. Note: This forecast is an outlier, but remains possible.

Finally, the UW WRF forecast, showing snow through Tuesday evening.

The UW forecast also appears to be an outlier, showing elevated snow from Convergence Zone bands producing 0.5-4" of snow north and south of Seattle, as seen above. It also shows 0.5-1.5" on the WA Coast, and 15-20" at the Passes.

Overall, the best chance for accumulating lowland snow will be in narrow Convergence Zone snow bands (Monday/Monday night) and scattered snow showers (Tuesday). Expect travel delays if crossing the Cascades or the Oregon Coast Range. Additionally, instability will create a slight chance of thunderstorms across the region on Monday. Colder temperatures, dropping into the mid 20s, are expected by Wednesday morning.