Monsoon Moisture Reaches Washington and Oregon

When one thinks of the Northwest during the summer, the word monsoon is not the first thing that comes to mind.  But during the last day, Southwest Monsoon moisture has spread from the southwest U.S. into our region.

It has already rained at Sea-Tac Airport and clouds have spread over western Washington.  

The water vapor channel of the NOAA GOES satellite clearly shows the plume of moisture heading directly over the Northwest.


And the visible satellite image this morning highlights the associated clouds over western Washington and northern Oregon


The radar image around 7AM indicates some showers moving up into our region.   My newspaper was a bit soggy this morning.


This moist air will be around this weekend and the air is unstable enough for more showers this afternoon, particularly over and east of the Cascade crest.

Over the 24h ending 5 AM Sunday, most of the showers will be over eastern Oregon (see 24-h accumulated rainfall below.  And some of these showers will be associated with thunderstorms. A few light showers could hit western Washington.


But Sunday is a different story, with northeast Washington and southern BC getting more moisture. Serious rain over some of the wildfires near Winthrop.


After today, there will be four warm days before the bottom drops out of our weather.   

Below are the forecasts for the NOAA GFS ensemble system showing the temperature at Seattle.  In an ensemble system, the model is run many times, each slightly differently.  

Today gets to around 80F, and the next four days are slightly warmer.  But then comes Thursday and BOOM...a big decline (the black line shows the average of the many forecasts).   There is some uncertainty in the forecasts, with a range of solutions, but most are MUCH cooler.   Same for Friday and Saturday.

Rain?  Chance of some very light errant showers over the weekend, but the rain chance really revs up on Thursday onwards, with many of the simulations showing rain.


As I noted early, this is quite a vigorous cool/wet event for midsummer, but I suspect it will be welcomed by many.  And it will reduce the wildfire threat for a while, assuming we don't get many lightning starts.








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