While much of the Puget Sound lowlands will be socked in by fog with stagnant cold air, the Cascade foothills are waking up Sunday to relatively warmer conditions in the mid 40 °s and mostly clear skies. You can thank light easterlies (gap winds) in response to an incoming front off the coast (shouldn’t impact us until overnight into Monday).
Clouds should begin to increase this afternoon and evening as a cold front approaches. Expect winds to shift overnight, blustery at times from the S/SW with rainy conditions Monday morning.
What may begin as rain at Snoqualmie Summit should change over to snow as air aloft continues to cool, ushered through by this system. Accumulations look to be on the light side; a couple of inches up to 6″ of new snow possible.
For the lowlands, showers should taper off by late Monday morning or early afternoon for most. A convergence zone over the northern Sound may then develop into Monday evening. These usually hold the potential of drifting south, bringing lingering shower activity to the central Sound, particularly further east.
High pressure should dominate for much of the remaining workweek. While AM fog probably returns to much of the Puget Sound, there’s another decent E-W pressure gradient that should set up to bring a return of light-to-moderate gap winds to Snoqualmie Valley Wednesday and Thursday.
While these winds blow, Lows should remain ~5+° warmer in the east foothills with a relatively sunnier AM forecast vs. areas out West (Issaquah, Bellevue, Seattle).
Longer range, for the next five days or so, there doesn’t appear to be any frontal systems strong enough to rain on this fair-weather parade.
While Western WA is smack dab in its rainy season, dry streaks of a week or so during late fall/winter here are not that uncommon. Enjoy it while it lasts!
Have a great week!