On the Edge for Snow

Posted by Rufus La Lone on

Friday November 25
Thanksgiving weekend update.  We’d like to keep this brief, but with the chance for SNOW coming, ‘yeah, right’.  Around here, we affectionately refer to snow as “The White”.  It is relatively rare for sea level snowfall around the region, so when there’s even a small chance for The White to occur, well, childlike excitement abounds; the forecast warrants a holiday Mug refill. 
A weak system will present rain and showers across the PNW today, Black Friday (most of the precip will fall north of Salem).  That will clear out, yielding a decent holiday weekend Saturday until after sunset.  The next, stronger AND COLDER system will move onshore, from north-to-south, while most of us sleep overnight Sat.  Windy.  This system has the potential to complicate holiday TRAVEL back home if one is driving over Cascade passes.  Rain will turn to showers on Sunday, with the air mass on the back side of this storm cold.  In fact, don’t be surprised to see snow & rain mixed (if not all The White at times) later on Sunday, esp in the northern Puget Sound area.  The warm ground, and diminishing moisture may limit accumulations, but it will be fun to watch.  
Quite chilly Monday & Tuesday (highs 30s to low 40s west side).  During this weekend storm, High pressure (>1040 mb) will begin to build over eastern Alaska, the Yukon (yes our fav place to peek for Arctic Events) and the Northwest Territories of Canada.  In the Wed, Thu, Fri period, Nov 30 -  Dec 2nd, we are anticipate the development of an “almost” modified Arctic Blast that will begin to shunt cold air out of the Fraser Gap, and eventually the Columbia River Gorge as another damp system tracks south along the coasts of BC, WA & OR.  Net effect: rain could turn to snow/rain mix at the surface; all snow above just a few hundred feet.  With the Low remaining off the coast (if verified), the colder air out of the Gaps will set up the snow or mixed pattern, esp overnight Thu.  On Fri, another coastal Low will follow the same path as above, with a bit colder air already in place, a snow/rain mix is probable, or it could remain as all snow if conditions are just right.  (We forecast an “almost” modified Arctic Blast because the bulk of the High pressure dome may skirt farther east, missing much of the region.  We’ll know more in our next update on the 28th.)
Saturday Dec 3rd The White is possible in portions of western OR, as the Fri Low mentioned above tracks into CA, drawing in cold air support from east of the Cascades as the moisture arrives.  Timing is everything.  IF this pattern verifies, a couple inches of snow is possible south of Salem.  By Sunday Dec 4, the moisture will be gone, the cold will be set in for a few days.  East winds will cease.  Morning fog possible.  
The week of Dec 5-9 is trending chilly & DRY, with an east wind picking up again, esp out of the Columbia Gorge.  Overall, though, temperatures will have moderated a bit, so not as cold as the weekend before.  Plain ole’ rain may return by the weekend of Dec 10.
—> Final note:  some model solutions dismiss the short-shots of moisture moving down the coasts, leaving the PNW mostly dry & frosty.  Southerly breezes also remove the surface snow threat, so position of the various Lows discussed above, is critical for valley snow/rain mix.  Either way, the coldest temps of the season are highly probable between now and Dec 6.  Snow events often take on their own, unplanned, attributes.  Be prepared.
Quip from the ’Net:  “I always knock on the fridge door before opening — just in case there’s a salad dressing."
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