Rod's Weather Headlines

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. 

TO RECAP:

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

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.  

Rod Hill 

This winter's outlook begins with what is fairly rare, a back to back La Nina winter season.  Our region is projected to have a moderate La Nina winter, matching last season's Enso cycle.  This will become just the 10th back to back La Nina since the cycle was documented starting in 1950.

{Before I continue, a thank you to Hillcrest Ski Shop for sponsoring my Mt. Hood Ski Forecast.  Please check out the friendly service and great selection in Gresham and online:  https://hillcrestsports.com/ }

Using history as a guide, this winter will have a greater possibility of being dry to very dry, then being a wet soaker.  Below are the main points this outlook will be graded on.  Notice colder than normal temps and a good snow chance round out the headlines. 

My projection calls for an equal chance of snow in December, January and February.   You may recall that last winter's outlook said no snow until January and a good chance of a big storm going into February.  The month that looks the most interesting to me is January.  Nearly all weather models show a colder and drier than normal month to begin the new year.  Take a look at the following weather model predictions: 

The flow pattern shows cold air building over the Rockies that could ignite a cold east wind into the valley, setting the stage for bitterly cold nights and possibly a snow and or ice storm. 

Here are my overall particulars, beginning with monthly temperatures.  Notice all months except November, show potential to be colder than climate average.  

Valley snow is touched on earlier, but again 4-6" of total snow is likely.  Past years show little confidence to forecast a big storm or simply a few smaller events, but each month starting with December has an even chance of snow on the ground. 

Skiers and boarders on Mt. Hood have good reason to feel excitement regarding the upcoming season.  While history shows this winter will likely have less total snow than last year, 80% of normal snowpack would be a good year and nearly equal to the 2017-2018 winter that enjoyed an early November start and generally a healthy base into the spring months!

The conclusions of this outlook are solely taken from NWS records and assume past back to back La Nina seasons will reflect our local weather in the coming months.  It is important to understand, nearly all data sets taken over decades of time include outliers and I rely on conclusions that are most likely to occur. 

Rod Hill 

April finished as the driest month in the record book for Portland, both at PDX and the downtown location. Records at PDX date back to 1941 and downtown back to 1871. Until we pick up a few good soaks, a much drier than normal spring will continue to be a big weather story. PDX is running at 29% of normal precipitation dating back to March 1st. Current May rainfall outlooks suggest a total between 1.00 - 2.00" at most for the month.

The graphic below shows total monthly rainfall compared to the climate average. 

Rod Hill 

(graphic courtesy of KGW TV)