FastCast—Saturday, Dec. 24 to Monday, Dec. 26:
What a week! It has been a downright crazy week of winter weather across the region, and threats aren’t over for all. The largest ice storm Western Washington has seen since January 2012 brought 0.1-0.4 inches of ice across the region, producing huge travel impacts and making roads very treacherous (lowland side streets could remain icy through early Saturday). All areas have warmed into the mid 30s to mid 40s and begun melting except for parts of the Willamette Valley, Whatcom County, Snoqualmie & Stevens Passes, and the Columbia River Gorge. These areas will be impacted by an additional 0.1-0.2 inches of ice (except 0.3-0.5 inches in the passes/gorge) through early Saturday, except continuing through Saturday for the passes. Expect significant travel disruptions over the passes on Saturday. Widespread 0.1-0.3 inches of ice is expected across Eastern Washington on Saturday. In the lowlands, a heavy rain event is ahead, with 0.75-2 inches of rain from Saturday morning to late Christmas Day (Sunday). The main concern will be urban flooding due to runoff and snowmelt, so be prepared for areas of standing water and large puddles. Temperatures will skyrocket into the upper 40s to low 50s, and snow levels will shoot up to 8,000 feet (but cold air will keep freezing rain at Snoqualmie & Stevens Passes). Winds will gust 20-30 mph, and 40-50 mph from Everett northward. Another moisture-laden system will approach the area on Monday, so stay tuned!
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Continue reading the full blog below!
In 24 hours, we’ve gone from our most widespread & impactful ice storm in 10 years to talking about heavy rain and much warmer temperatures.
Below is the European model forecast, showing total rain through Christmas night.
Expect 1-2 inches across the lowlands, with less in the Olympic rain shadow. The mountains will be soaked with 3-5 inches of rain, and the coast will pick up 1.5-3 inches.
However, the freezing rain threat is far from over, especially for Snoqualmie and Stevens Passes and the Columbia River Gorge. Below is the European model forecast for freezing rain through Christmas night.
Expect 0.1-0.2 inches of freezing rain for the Northern Willamette Valley and Whatcom County. Impactful freezing rain is expected for Snoqualmie & Stevens Passes and the Columbia River Gorge, with 0.5-0.75 inches of ice accretion expected. Major travel impacts are possible with this setup. Additionally, expect 0.1-0.3 inches of ice across Eastern Washington.
Freezing rain will linger longest in the Columbia River Gorge and Snoqualmie & Stevens Passes. Expect freezing rain to end in these locations by Saturday evening, though the impacts of 0.5-0.75 inches of ice will remain into Christmas.
Freezing rain should end across the Pacific Northwest by Christmas night.
Let’s focus on the heavy rain threat for the lowlands. Below is the UW model for the amount of water vapor in the atmosphere at 7 AM Saturday.
This shows a large area of deep subtropical moisture moving into Western WA & OR. This is what will bring significant rain totals through Christmas, with another system bringing another round of heavy rain starting Monday.
High-resolution forecasts, while not always good with snow, are helpful in pinpointing areas of heavier rain totals. Below is the NAM forecast for rain through late Christmas night.
The NAM forecast shows 0.75-1.5 inches of rain across the lowlands, with a pronounced rain shadow on the NE Olympic Peninsula. The NAM gives the coast 1.5-4 inches, and the mountains get 3-8 inches.
Next is the HRRR forecast, which paints a similar forecast through Christmas evening.
The HRRR shows 0.75-2 inches of rain in the lowlands, following the pattern of the most rain from Everett to Tacoma. There is a pronounced rain shadow on the NE Olympic Peninsula and Whidbey Island. The coast receives 1.5-3 inches, and the mountains get soaked with 3-8 inches.
What about temperatures? We will have our warmest temperatures (by far) in over a week, with some areas being 20-30 degrees warmer than 24 hours before. Below is the European model’s forecast for high temperatures on Saturday.
What an increase from the past two days. Expect lowland highs in the mid 40s to low 50s, with potential mid 50s on the coast! However, notice the lingering cold air in the Columbia River Gorge and Eastern Washington, which will aid in producing freezing rain. Highs in the Gorge and Eastern Washington will be in the upper 20s to mid 30s, with some areas getting above freezing, particularly out of the topographic bowl of the Columbia Basin.
Finally, a look at the 24-hour temperature increase at 10 AM Saturday.
Expect Saturday morning’s temperatures to be 10-20º warmer than Friday in the lowlands, and 15-25º warmer in Eastern Washington and the Willamette Valley!
Stay tuned, as much more stormy weather is ahead. I will also post an ice storm recap blog on Saturday, including photos!
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