Update For Heavy Rain Event

By Rod Hill on 2021-11-10

Residents of the northwest bracing for possible heavy rain event this evening through Friday night. 

A weak atmospheric river will accompany a warm front tonight to bring hours of steady rain, heavy
at times into Thursday morning.  Widespread rain tonight will drop at least .50” of rain over Portland
and Salem with valley amounts possibly nearing an inch.  The warmer air will lift snow levels above
8,000’ by morning, meaning all rain at Mt. Hood resorts.

While surface winds will be breezy, south 10-20 mph, wind will generally not be a concern through 
the forecast period.  People living at elevations above 1,500 feet should expect constant southwest 
winds between 20-30 mph.  The warm moist air will bring rising temps overnight into Thursday morning,
with much of the Portland area waking up to 55 degrees, rain and ponding of water on area roadways. 

A forecast update shows the main fetch of steady, heavy rain will push north of Portland into Washington
during the day Thursday, bringing a respite of steady rain.  Daytime rain amounts Thursday may average
as little as .25 inches.  Valley high temps will warm into the low 60s. 

Rain picks Thursday overnight into Friday morning in what could be a 2nd period of steady, heavy rain 
as a cold front drops southward into our region.  The front may become nearly stationary during the 
day Friday with the atmospheric river transporting rain over the frontal boundary, producing valley rain 
totals well over an inch during the day and possible 1.50 inches.  As the front drops through our region
Friday night, rain ends for a dry Saturday. 


2 heavy rain episodes - one tonight and a 2nd Friday daytime. (possible rain break of sorts Thursday afternoon)

Valley rain total:  2.00 -3.00”

Coast rain total:  2.50-5.00”

Coast Range and Cascades rain total:  6.00” and possibly 10” of total rainfall in some drainage basins. 

Smaller rivers (meaning not the Columbia or Willamette) may reach flood stage Friday pm hour into the night. 
High water spots become possible Thursday morning and again during the day Friday. 

Mudslides will be a concern over wildfire burn scars. 

Rod Hill