By Rod Hill on 2021-11-09
A warm front Wednesday evening will lead to steady rainfall overnight, adding up to .50" in Portland and beginning a stretch of mostly steady, heavy at times rainfall through Friday evening. A weak atmospheric river will pump Pacific moisture into a convergence zone along a warm front to stationary boundary Thursday. The moisture flow continues Friday as a cold frontal boundary slowly drops south through our region.
Weather models show more than inch of valley rain Thursday and possibly an inch of rain Friday, making for 60 totals between 1.50 and 3" of rain over the Portland metro and much of the I-5 corridor from Albany to Longview. The Coast Range and Cascades could see rain totals of 6-12" through the period, while the coast sees 2.50-5.00 inches. High water spots or urban flooding are expected, along with possible river and stream flooding Thursday night into Saturday. Mudslides in burn scar areas are also a concern.
Snow levels will be high at 8,000' and above Thursday and Friday, meaning heavy rain in the mountains. Elevations above 1,500 feet may see a constant southwest wind between 20-30 mph through much of the period.
Dry weather is expected to return Saturday, either morning or afternoon.