Next System Bringing Heavy Mountain Snow, Significant Weather Possible Saturday

FastCast—Wednesday, Dec. 8 to Saturday, Dec. 11:

The next weather system arrives on Wednesday, bringing breezy conditions (25-35 mph) in the Lowlands, stronger (35-40 mph) in the North Sound. Showers are expected at times, but likely not in the metro area, which will be rain-shadowed. The biggest impact from this system will be heavy mountain snow. 12-18 inches of snow is expected at Snoqualmie and Stevens Passes through Thursday morning, with snow rates of 1-2” per hour possible, due to strong localized snow bands due to the Convergence Zone. This is particularly likely on Snoqualmie Pass. Mountain pass travel on Wednesday and Thursday will be challenging, so be prepared for delays and winter storm conditions. Breezy and showery conditions remain on Thursday. The next system arrives late Friday and lasts through Saturday, with significant impacts possible. Heavy rain (0.5-1.5”), strong winds (40-50+ mph), and significant mountain snow totals (1-2 feet) are possible by Sunday. Stay tuned for more information on this system. Expect highs in the low to mid 40s and lows in the mid 30s to low 40s. 

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The next weather system arrives in Western Washington on Wednesday, primarily bringing heavy mountain snow and breezy conditions. 

Winter Storm Warnings have been issued in the Cascades for 12-18 inches of snow through Thursday. Below is the Euro model forecast for snow through Thursday night.

This forecast generally reflects the consensus of 12-18 inches. Multiple Convergence Zone snow bands will likely form around Snoqualmie and Stevens Passes on Wednesday and Thursday, and these bands will have snow rates of 1-2 inches per hour, creating winter storm driving conditions on the passes. The highest likelihood for heavy Convergence Zone snow is on Snoqualmie Pass.

Breezy conditions are expected on Wednesday, lingering into Thursday. Gusts of 25-35 mph are possible in the Interior, with higher gusts of 35-45 mph possible in the North Sound and on the coast. Below is the high resolution HRRR forecast for 6 AM Wednesday.

Showery weather will prevail on Friday, and breezy winds will begin to increase by Friday night. Rain and mountain snow will begin Friday evening as well. 

While details are still uncertain, forecast models have been agreeing on heavy rain (0.75-1.5”), strong winds (40-50 mph interior, 50-60 mph coast & North Sound), and significant mountain snow (1-2 feet possible). 

One thing is certain…after a relative lull in rainfall, substantial rain will fall over the next week (Euro forecast through the 14th below).

Stay tuned for more information about the Saturday storm!