Fall Wx Arrives

Posted by Rufus La Lone on

Monday September 18
A few adjustments in the long-range outlook, so let’s review the latest.
Cooler temperatures have arrived, so too, will a rapidly moving cold front later tomorrow.  The Low dropping down the BC coast late Tue is weak, but a bit more organized than the one that brought today’s cloudiness & milder temps.  Therefore, we can expect a few showers - mainly north of Salem overnight Tue into early Wed; similar for the Puget Sound area.  Enough precip to wet the pavement, yet not enough to provide relief for dry soils.  After the front passes, it will be turn FALL COOL this Wed & Thu.  Warmer on Fri (upper 70s, maybe 80-82 in the southern Willamette Valley, south). 
Overnight Fri on into the coming weekend of Sept 23,24, a notable shift in the overall weather pattern will begin.  Model solutions suggest that the Gulf of Alaska will be ‘filled’ with a broad Low pressure trough, with subsequent ‘waves’ of fronts spinning closer & closer to the PNW in the Sept 23-26 timeframe.  Early on, it looked like the rain fields from the string of systems would steadily move onshore during that weekend.  Now, the broad Gulf trough may remain far enough west to delay arrival of steady rain fields for a few more days.  That said, the first band will move into Vancouver Island & far NW WA as early as Friday night - so expect some rain there.  The weekend is likely to remain dry & mild elsewhere (70s).  The Fall Equinox happens the 22nd at nearly midnight; the 23rd at 2:50 a.m. for the eastern time zone.
A deep, powerful Low pressure center is modeled to form late Sunday well off the coast of BC.  There will be a moderate-to-heavy rain field move over Vancouver Island & southern BC on Mon the 25th; the rest of the PNW will, again, miss out most of the precip, as the front will weaken considerably before it moves over west side locations on Tue.  Still, we can expect showers around western OR & SW WA Tue & Wed, Sept 26,27.  Mainly a cloud event, not a drenching rainstorm.  This could change, but for now, that ’s what the models indicate.  
1st big fall storm.  While precise timing is uncertain, a couple stronger systems are currently charting for Thu and Fri Sept 28, 29.  WET and WINDY.  California may get in on the action, as the Fri Low spins heavy rain into the Golden State.  Best to plan on a rainy weekend, Sept 30 - Oct 1.
Early October is coming into view.  The main aspect is for the Gulf of Alaska to remain under a broad trough of Low pressure - which typically leads to fall storms over the PNW.  We’ll see.
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