Continuing On the Edge

Posted by Rufus La Lone on

Monday November 28
We will continue on the edge for low elevation snow for the next several days.  Time for that refill, Patron.
It’s always difficult to get snow at the surface in the PNW, mainly because we are so close to the Pacific, which holds temps up.  The pool of cold air on the east of the Cascades will not be quite as cold as forecast several days ago, hindering our chance for west side snow.  However, there will be periods between now & Sunday that may allow for cold air to be drawn west to mix with the marine moisture resulting in a snow/rain mix at the surface, and snow in the foothills.  
Showers today will diminish before the next system moves in from the NW Tue & Wed.  The mid-week storm will be rather strong, with a Low pressure center deepening to approx 980-984 mb when it is west of Vancouver Island.  This will cause surface winds from the south to keep valley floors warm enough to hold off any valley snowfall.  That said, depending on the position of that Low, colder air drawn in from the east could keep the air mass cold enough for snow/rain mix, or just snow at times, esp later Wed into Thu as that Low drift south off the coast of Oregon.  You’re right: not a definitive forecast, because we remain On the Edge, indeed.
Another ‘repeat’ storm is modeled to follow nearly the identical path on Fri Dec 2.  Yep, there will remain the threat for low elevation snowfall.  Either way, it will be a very chilly, wet period as this week ends.  Sat & Sunday are trending drier, with chilly air mass and a moderated east wind.  Sunday night the next Low tracks just off the coast of BC and then right over OR.  Rain at the surface, snow in the coast & Cascade ranges.  North Puget Sound could see snow/rain mix, as the Fraser Outflow will turn on again, rushing colder, continental air into the region.  Familiar pattern.
A classic wet, mountain-snowpack-building pattern will set up for 1st full week of December.  A large pool of very cold air is charted to settle over the Gulf of Alaska during the week of Dec 5-9.  By mid-to-late week, that colder air will drive wet systems into the PNW, for very low elevation snowfall.  Too early to predict valley snow, but, if models verify, snow levels will be quite low (500-1,000 ft).  This pattern will be quite different from the current one because the coldest air will arrive from the northwest, hence any chance for snow will not be predicated on an east wind.  We’ll monitor this closely.  California should get some precip out of this pattern, late week.  
As the weekend of Dec 10,11 gets underway, an east wind may develop as High pressure, centered over the Continental Divide pushes air towards the PNW coast.  Concurrently, a Low will be moving south off the coast, missing the PNW, contributing to a large pressure difference, which sets up the strong east winds.   RAIN should return during the week of Dec 12-16, some of which may be moderate-to-heavy.  
Well, that's the current long-range outlook.  Change is inevitable, so keep that Mug of yours handy and step back into The WxCafé™️ on Friday for the latest revision.
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