The White is Probable

Posted by Rufus La Lone on

Monday November 29

That’s right, 'The White’ (our affectionately coined term for SNOW) is looking probable for the PNW later in December.  While others may brush aside atypical patterns that extended-range models project, The Weather Café®️ doesn’t hesitate to give Patrons the heads-up and the preparation time needed to get ready for unusual weather events.  Snow, at the surface west side of the Cascades, is, indeed, one of those unusual events worthy of preparation (and fun anticipation, for many).  So, Mug up, Patron.
The flooding situation up in NW WA and BC will continue to dominate everything through Wed night this week.  Later Wed, colder air aloft will help ‘hold’ some of the excessive precipitation in the mountains as snow, but still, record breaking rains have sent several rivers above flood stage, yet again.  It will dry out up north late week, as temperatures begin to lower several degrees, esp by the Dec 4,5 weekend .  
For a few days this week there will be a ‘zonal’ west-to-east flow of the ‘jet stream' with cooler air over WA (from roughly north of Chehalis) and mild air over OR.  That same flow will train moisture into the far NW, as noted, and keep OR & southern ID on the mild, DRY side.
Model runs have generally settled on the first weekend of Dec being relatively dry, as the pattern mentioned above continues.  By late Sunday or early Monday, a relatively strong ‘warm’ storm will move onshore north of Vancouver Island, ushering in a warm southerly WIND and wide-spread rain (freezing level jumps again).  Breezy, showery early Tue Dec 7 - Pearl Harbor Day - then a brief stop in the precipitation late Tue & Wed next week.
Now, the interesting transition.  High pressure ridge over the western Alaska (cold up there, with temps in the -35 to -42 degrees F recently), will begin to chill down the air mass over the Gulf of Alaska.  The resulting broad cold trough is modeled to begin approaching the PNW overnight Wed Dec 8.  Current model solutions continue that cold movement all the way south over WA, OR and northern CA as the week of Dec 6-9 ends.  Heavy rain, WIND and a rapidly lowering freezing level will be in play for the PNW.  In fact, by Fri the 10th, the air aloft over from NW OR north looks to turn cold enough for surface snow, esp north of Portland.  If not at the surface, then as least just a few hundred feet above sea level.  Have winter travel gear ready.  Rain over southern OR & northern CA could be quite heavy.  
Another pair of powerful Pacific storms may arrive from the NW on Sat/Sun and Sunday night Dec 12.  Initially, southern winds will lift the freezing level for plenty surface RAIN & mountain snow, before turning colder again, with a decent combo of moisture & temperature on the backside of the second storm to drive snow down to near, or at, sea level in many places from Eugene north.  It will be a very windy weekend, as well.  Blizzard conditions for all mountain pass travel.
Snow showers, if the whole pattern mentioned above verifies, will continue into Tue night, Dec 14.  Some models solutions set up a strong winter temp outflow from the Fraser Gap and Columbia River Gorge by mid-week.  Any snow is likely to hang around for a few days.  
Second Cup:  of course, all of the above is simply a model projection.  However, a cold, possibly surface-snow-pattern has been popping up on the wx models for quite some time now.  A few model runs build a mild High pressure ridge over the west coast, keeping the cold event away from much of the PNW for an extra few days, but none remove ‘The White’ threat completely in the time-frame of Dec 12-15.  Patrons know that over the past 27 years, these long-range projections have been accurate enough to warrant preparations, just in case.  We’ll be a few days closer to said events by our next Mug here, so stay tuned.
From an actual Church Bulletin: “On Sunday, a special collection will be taken to help defray the expense of the new carpet.  All those wishing to do something on the carpet, come forward and get a piece of paper."
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