Major Storm Bringing Blizzard Conditions, Strong Winds, and Heavy Rain

For the first time since December 2012, NWS offices in Seattle, Portland, Pendleton, and Spokane have issued Blizzard Warnings for the Cascades, Olympics, and Blue Mountains. 

A significant mountain snow event is ahead as a multi-faceted storm impacts the region. Let's take a look at the forecast, starting with the European model forecast for snow through Tuesday night.

This forecast shows 15-30 inches of snow for the Cascades through Tuesday night. Snow will start Monday morning, continuing through late Tuesday, but becoming showery. Snoqualmie Pass will switch over to rain sometime late Monday night or early Tuesday morning ahead of the cold front, before dropping below freezing again on Tuesday.

Also, notice the potential for 0.5-2" of snow for the Bellingham and Vancouver BC areas, plus 1-4" of snow for most of Eastern WA except the lower Columbia Basin. The European model also shows a weak system bringing a potential 1-3" of snow to the Portland & SW WA regions on Wednesday morning.

Let's compare this to the high-resolution NAM forecast for snow through Tuesday night.

This forecast shows 12-18" of snow at the passes, with 2-3" of snow for Spokane and Pullman, plus a chance of a trace to 2" of snow for Northern Whatcom County and Vancouver BC.

Finally, let's zoom into the Cascades and take a look at total snow through Tuesday night from the ultra high-resolution UW WRF forecast.

This forecast shows 16-24" of snow at the passes, with additional areas of snow on the Eastern slopes of the Cascades, Northern Whatcom County, and along I-5 south of Olympia.

By itself, 1-2 feet of heavy snow is impactful, but when you add in strong winds, it becomes a dangerous and impactful winter storm. This storm will cast a strong pressure gradient across Washington state, bringing windy conditions to the entire region. Below is the European model forecast for peak winds (in knots) for Washington, through late Tuesday.

Expect winds gusting 40-50 mph in the lowlands and 50-60 mph on the coast, peaking Tuesday. A strong westerly wind surge down the Strait of Juan de Fuca will likely bring damaging 60-65 mph gusts to west-facing shorelines of Whidbey and Fidalgo Islands on Tuesday afternoon. Note that winds across the Cascades, Olympics, and Blue Mountains will likely gust 45-60 mph (higher at higher elevations), which could cause blizzard conditions (more on this below). Eastern WA will also gust 35-45 mph on Tuesday.

Next, let's take a look at the HRRR high-resolution forecast for peak winds.

This forecast shows stronger winds for the entire region, with the lowlands gusting 45-55 mph, the coast gusting 50-65 mph, and a westerly surge bringing gusts of 55-65 mph to Whidbey Island, with the entire Strait hitting 50-60 mph in this forecast. Eastern Washington will gust 40-60 mph in this forecast, strongest from the Tri-Cities to Spokane. The mountains will gust 50-65 mph in this forecast, strongest at higher elevations.

Due to the combination of a major snow event and a windstorm, blizzard conditions are expected in the Cascades, Olympics, and Blue Mountains. The map below from NWS Seattle shows where the Blizzard Warning is in effect (red).

A Blizzard Warning is in effect for most of the Cascades and all of the Olympics. This is the first time since December 2012 that a Blizzard Warning has been issued for the western slopes of the Cascades and the Olympics. Snow will be heaviest late Monday night through Tuesday, with winds strongest from early Tuesday through the evening. A "blizzard" is defined as winds of 35+ mph and visibility of 1/4 mile or less for 3+ hours during a snowstorm. While blizzard conditions will not be happening everywhere in the warning area at all times, those conditions are expected in the Cascades, Olympics, and Blue Mountains.

Finally, let's take a look at the rain forecast through Tuesday night. Below is the European model forecast for rain through Tuesday.

In the lowlands, expect 1-2" of rain through Tuesday night, most from Tacoma south. The coast will receive 2-3". All of this will be snow in the mountains.

Lastly, here is the GFS (American) model forecast for rain through Tuesday.

This forecast, while slightly drier, shows 1-1.5" for the lowlands with a rain shadow over Whidbey Island. The coast could get 1.5-2.5" of rain out of this system.

Overall, a very dynamic storm system is ahead for the Pacific Northwest. Stay tuned for more updates on my Twitter and on Michael Snyder's Pacific Northwest Weather Watch YouTube channel for daily briefings. Stay safe out there!