A very active precipitation period is on tap for the next 24 hours over the area with moderate rain for most of Washington. Satellite indicates a deep and cold upper level trough over British Columbia with the dynamic foot of the trough carving into Washington and Oregon this morning.
While there is no real favorable moisture tap, the dynamic, slow moving frontal system will be strong enough to produce a sustained period of valley/basin rain and mountain snow over pretty much the entire forecast area. Tonight, rain will switch over to snow in the northern Cascades and mountains of northeast Washington and could receive 2-4” of snow which could make road surfaces across the passes become snow covered and slick. Winter Weather Advisories will likely be issued for tonight and Friday morning.
A slow warming trend and drier weather will arrive for the weekend and Monday bringing sunny skies, light wind and temperatures near 60. Then, a return to cool and wet weather Tuesday through the remainder of next week as another large low pressure system moves into the Pacific Northwest.