Monday December 20
For those that dare to dream of a White Christmas — grab a Mug, fill it, and let’s see if that dream will come true this year.
In our last report, we repeated one of the frequent attributes of wx models - that earlier prognostications often end up being correct. On Dec 13 we wrote extensively about what could happen in the period from Christmas Eve through the following week — that a White Christmas was possible across most of the PNW (if you still have that email, read it again, as that will best explain the dynamics of what may happen later this week). Now, what gives?
We have a better than 50% chance for a White Christmas here in the Willamette Valley, SW WA, Puget Sound environs, Lynden/Abbotsford, etc. What we have coined ’The Juneau Low’ — our Christmas Present from Alaska — will, by tomorrow Dec 21, begin to drop south along the Alaskan Panhandle & coastal BC to arrive in time for the big holiday. The cold-centered Juneau Low, along with additional Lows will have enough trajectory over the eastern Pacific to pick up moisture and roll it onshore for surface snows, on and off, from Christmas Eve into early 2022. Remember 2008? Cold air aloft should keep the snow around between snow systems. Some of the Lows will bring rain at first, then back to snow.
Cold Arctic air pooling over eastern Alaska/Yukon will also be shifting southeast, setting up the classic cold outflow from the Fraser Gap (and post-Christmas, the Columbia River Gorge). Temperatures will plummet as the modified Arctic air gushes through the Gaps (Fraser Gap WINDS will be potentially damaging strong. Prepare.) We will get into the subfreezing temperature outlooks in a later report, for now, be sure to prep business & residential plumbing and thawed livestock water supplies, as this event could extend several days overall. Travel will be challenging at all elevations.
How much snow? Projections are always iffy, but for now, we will peg 2”-6” snow south of Salem, 6”-8” Salem north, similar amounts over much of western WA between Dec 24 & Jan 4. Bellingham north will likely deal with snow drifts in the usual problem areas. Again, all of this snow dream stuff could be just that, a dream. However, there is less uncertainty as confidence is growing throughout wx forecasting industry in the PNW that The White is quite possible as the holidays get underway.
For now, the heavy rain (Mary’s River at Corvallis at flood stage) will cease as this day (Dec 20) progresses. Tue should be mostly dry and relatively mild. The next wet, breezy system is due sometime on Wed. This one is the first of upcoming Lows spinning south along the Alaska Panhandle & BC coast. The second one will combine with the 1st to become our Christmas Present, setting up the snowy forecast you just sipped through.
California will get in on the action, first as rain/wind storms, then the potential for low level snowfall as far south as the Bay Area. News time, if this verifies. The Sacramento Valley could get a hard frost if the sky clears during Christmas Weekend, and again in early January. Bundle up; protect plumbing.
“Every area of trouble gives out a ray of hope, and the one unchangeable certainty is that nothing is certain or unchangeable.” -Pres. John F. Kennedy.
Copyright © 1994-2021 - All Rights Reserved - The Weather Café ®