Last System of January, Then A Long Stretch of Dry Weather

FastCast—Thursday, Jan. 20 to Thursday, Jan. 27:

A weather system will move through Western Washington late Wednesday and through Thursday. Expect 0.25-0.6 inches of rain by Thursday evening, most in potential Convergence Zone bands from midday to Thursday night. Additionally, 2-6 inches of snow will fall at Snoqualmie and Stevens passes, with more in higher elevations north of I-90. Convergence Zone bands may bring briefly heavier snow. Breezy conditions are possible on Thursday as well, mainly north and south of Seattle, with gusts of 25-40 mph possible. A large high pressure ridge will build off the coast starting on Friday. This will bring at least 5 days of dry weather with morning fog and afternoon sun. (Uncertainty does remain regarding how long fog will last each day). Highs will be in the mid 40s to low 50s and lows will be 30s. Lows near freezing are possible, so there is a potential threat of freezing fog. With relatively little wind and consistently dry conditions, air stagnation and degraded air quality may become an issue. Stay tuned! Also…this will likely be the longest dry stretch (by far) since September!

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The last weather system of January will move through late Wednesday into Thursday. The rain forecast (HRRR model) through Thursday night is below.

Generally, expect 0.25 to 0.5 inches of rain around the lowlands. A decent Olympic rain shadow is expected due east of the Olympics and to the Seattle/Everett area. North of Everett, 0.6-1 inch of rain is expected, and about the same on the coast.

Mountain snow is possible too. Expect 2-6 inches in the passes, with more at higher elevations between Snoqualmie and Stevens Passes. Briefly heavier snow is possible if Convergence Zone bands align with the passes. The HRRR snowfall forecast through Thursday night is below.

Breezy conditions are also possible north and south of Seattle on Thursday. Gusts of 25-40 mph are possible, strongest north of Everett and along the Strait of Juan de Fuca.

A large high pressure ridge will build off the coast starting Friday, seen below on the European model.

This ridge will bring consistent dry weather to Western Washington starting Friday. Expect morning fog each day, with some days potentially remaining foggy in the lowlands. High temperatures will be in the mid 40s to low 50s, with lows in the 30s. 

On the WA/OR coast, downslope flow will bring much warmer temperatures, with highs in the mid to upper 50s on the Washington coast, and potentially into the 60s on the Oregon Coast. The European model high temperature forecast for Sunday is below. Notice the warmer temperatures on the coast.

This consistent dry and calm weather with little wind will elevate the potential for air stagnation starting this weekend. Stay tuned!