Updated Thursday at 11:54 a.m.
Welcome to the wettest day since last January. Rainfall rates over the Olympics and northern Cascades have exceeded 0.50" per hour as the "Pineapple Express" of mild, Pacific moisture streams overhead. This tropical-like deluge will result in an unusual amount of rain (4-6 inches) in the northern Cascades, the runoff from which could cause minor to moderate flooding along the Nooksack and Skagit River. Burn scars left over from summer wildfires in the Cascades will also be prone to mudslides and debris flows. Flood Watches have been posted across 9 counties, including Snohomish and King County. The Snohomish and Snoqualmie River will rise as well but likely stay just below flood stage.
The rain coverage and intensity is increasing across Puget Sound with the heaviest rain of the day for Seattle falling during rush hour (4-6 PM). Low visibility and urban street flooding could hinder the drive home, especially considering a period of strong winds (gusting over 40 mph) will further strip the leaves off the trees to clog the drains.
Eventually, the fire hose of moisture shuts off early Friday morning. Sunshine soon returns tomorrow afternoon, a good omen for the holiday weekend ahead. Clear conditions combine with the ground moisture leftover from this atmospheric river event to form fog Saturday and Sunday morning.
Happy to forecast a dry Halloween this year, but the extra layer will feel good for trick-or-treating as temperatures dip into the 40's after sunset Sunday night.
Meteorologist Kristin Clark
The KOMO4 Forecast Team
Today's Record Temperatures