FastCast—Monday, Nov. 7 to Thursday, Nov. 10:
After a very active weekend, a much colder pattern is ahead. A localized chance of lowland snow is possible, primarily on Monday morning. This chance is highest on the Northern Olympic Peninsula, Whatcom County, hills in the San Juan Islands, the western Kitsap Peninsula, and the hills on the Central Coast. A lesser chance exists for the Cascade foothills. If any snow does fall, accumulations will be around a dusting to 2 inches, highest in areas enhanced by offshore flow (Northern Olympic Peninsula, western Kitsap Peninsula, and potentially Whatcom & San Juan Counties). As always, the snow situation will be very localized. Areas in the mountains above 1,500 feet will receive 3-10 inches, with some areas getting over 18 inches. In the lowlands, 0.1-0.5 inches of rain will fall through Monday evening as showers move through. It will also be much colder. Highs through this week will only reach the low to mid 40s. Morning lows will be by far the coldest of the season, dropping into the upper 20s to low 30s in the interior lowlands and potentially into the low to mid 20s in the North Sound. In addition to the cold, breezy (and biting) northerly winds are also ahead. Gusts around the region may reach 25-30 mph, peaking on Tuesday. Wind chills of 25-35º are expected through Wednesday, coldest on Tuesday evening and Wednesday morning. Even colder wind chills of 15-25º are expected from Mount Vernon northward and in the San Juans.
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A much colder pattern is ahead for Western Washington, with a slight chance of lowland snow for select areas. The highest chance of lowland snow will be on Monday morning. We will take a look at a few forecasts to find a consensus for snow.
Below is the NAM forecast for snow.
The NAM shows accumulations of 0.1-2 inches for the Northern Olympic Peninsula, the Cascade foothills, the San Juan Islands, and the Kitsap Peninsula.
Let’s compare this to the HRRR forecast.
This forecast shows less snow for parts of the lowlands, only showing 0.1-1 inches for small areas of the foothills, the Northern Olympic Peninsula, and the higher hills on the Central Coast.
One more forecast available to us is the very high-resolution UW forecast, seen below.
This is by far the snowiest forecast, showing accumulations of 0.5-3 inches for the Northern Olympic Peninsula, the Central Coast hills, and areas from Everett northward. The UW forecast shows a significant upslope snowstorm on the Kitsap Peninsula and Admiralty Inlet area, with huge amounts of 4-10 inches. This is unlikely to occur.
These three forecasts show that the highest chance of a dusting to 2 inches of snow will be on the Northern Olympic Peninsula, Western Kitsap Peninsula, the hills on the Central Coast, and San Juan & Whatcom Counties. Outside of these regions, 0.1-0.5 inches of rain is possible in the lowlands through Monday.
Additionally, significant snow will continue in the mountains, with 6-12 inches at the passes and 18+ inches at higher elevations. Snow showers will cease by late Monday.
In addition to lowland snow, temperatures will be much colder than recently this week. Below is the NAM forecast for highs on Monday.
Highs in the lowlands will reach the mid 40s. In the mountains and some areas of Eastern Washington, highs will only reach the 30s.
Lows will be the coldest of the season. Below is the European model forecast showing lows on Wednesday morning.
Note that lows for cities near the water will be higher than lows a few miles inland. With that in mind, expect morning lows dipping into the upper 20s to low 30s for the lowlands. The foothills and areas from Everett northward will drop into the mid 20s, with isolated readings in the low 20s. Eastern Washington and the mountains will be very cold, with lows in the low teens to mid 20s.
One more aspect of this upcoming colder weather will be the biting northerly winds expected after the showers clear late Monday. Offshore winds will peak on Tuesday, with gusts of 20-35 mph for the lowlands, strongest near the water. Areas in Whatcom and San Juan Counties have a potential for gusts up to 40 mph due to Fraser River Outflow.
Below is the European model forecast for gusts on Tuesday afternoon.
Northerly winds will peak in the lowlands on Tuesday evening, and the most noticeable impact will be cold wind chills. During the day Tuesday, expect wind chills (feels like temperature) to be in the low to mid 30s throughout the region.
By Wednesday morning, winds will be a bit weaker, but with colder temperatures, wind chills around the area will be quite cold. This is seen in the European model wind chill forecast for 7 AM Wednesday.
On Wednesday morning, expect wind chills in the mid to upper 20s for the interior lowlands, and in the mid teens to low 20s north of Everett. Eastern Washington and the Cascades will have wind chills in the upper single digits to upper teens.
This is by far the coldest air of the season, and its impact will be most noticeable with northerly winds and in the cold mornings. For updates on lowland snow, follow NWS Seattle on Twitter.
Blog note: I will post an update on the cold weather situation on Monday night, but will not have another update until Thursday night or Friday, as I will be traveling.
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