Arctic Event Possible

Posted by Rufus La Lone on

Monday December 12
Well, the extended outlook has taken quite a turn toward Winter.  We will present the possibilities knowing that all could change.  Before filling your Mug, please accept an opening commentary.
’Table ☕️ Talk' — While the coffee is getting ready, a few comments.  Long-time Patrons here (as we’ve started the 29th year of writing these forecasts), know that the crystal-ball weather models used to build our forecasts have lots of variability.  A few years ago, one model - the GFS (U.S. NOAA) - underwent revisions and updated ‘code’ to improve the charting of potential atmospheric changes.  It is the personal opinion of our staff (me, myself & I), that the variance in model outlooks has widened.  Concurrently, the earth’s climate continues to change (as it has always done, human-influenced or not) which may or may not be accounted for in the model projections.  We request Patron tolerance for what can be quite a difference in the weather forecast vs what actually happens.  As difficult as it is to be ‘spot on’ in forecasting weather for your planning purposes, we will not back off presenting ‘what if' scenarios to help Patrons.  Our motto has always been “be prepared, just in case.”  
Ah, now the coffee is ready.  Mug is full.  Onward.
This week’s weather will start out on the calm side, with spotty fog possible along with air stagnation.  By Thu Dec 15, high pressure will rapidly build to the E-NE, setting up STRONG outflow WINDS from the Fraser & Columbia Gaps.  This will help ‘clear the air’, if you will, but also make traveling east along the Gorge a real grip-the-steering-wheel experience.  We will notice a drop in temperature overnight in wind sheltered areas.  With the weekend will come the potential for SNOW or a mix of snow/rain.  Yes, it is becoming more-and-more probable, if the models verify.  Our 'Table Talk' comes into play now.
Dec 18 - 23
Arctic Cold.  The E-NE winds will subside briefly early on Saturday the 17th right before the leading edge of an Arctic Cold air mass begins to shift south out of eastern Alaska & The Yukon.  Barometric pressure is charting well above 1050 mb (we find it hard to fathom the forecast of 1060s plus mb on the GFS charts).  With a surface Low possible along the BC coast following a similar track, SNOW is probable in the Sunday / Monday Dec 18,19 period.  The system may not carry much moisture, but it doesn’t take a lot to witness The White.  Areas with snow would be Salem north.  The air could cool down rapidly west of the Cascades, if the Low trajectory is just right.  Generally, though, the coldest event of the season is charting to drop into the PNW and the middle of the U.S. starting this weekend.
The E-NE winds will HOWL Monday through Friday Dec 19-23.  A second shot of colder Arctic Air arrives.  Seriously, wind damage possible for some trees, as very cold HEAVY air settles into the eastern basins of WA, OR and to the east.  The week should be DRY & cold.  Single digits temperatures possible east of the Cascades; upper teens to low 20s west side, out of the wind.  Right now, the models build such a High Dome of pressure, that cold air will really smash west out of the Gaps.
Another scenario in the Dec 18-23 period is that the first ‘drop’ of cold air from the north skirts east of the Continental Divide, keeping the PNW on the chilly side, with no threat for snow showers on Sunday the 18.  However, that second, colder blast from the Yukon, if it happens, would greatly intensify the pressure difference east & west of the Cascades on Canadian Coastal Mountains with WINDS notably stronger than the first shot.  Stay tuned
Christmas weekend.
With either scenario, models bring Pacific storms into the region from the west during the holiday weekend.  That means the transition from cold to mild will be quite messy.  Bad timing.  We could experience a day or two of snow, then freezing rain, then rain. The degree of each type of precipitation we have will depend on how which of the forecast discussed above pans out.  For now, we are suggesting that snow/freezing rain is possible on Christmas Eve (more snow than freezing rain for NW WA, to start with anyway).  Valley RAIN on Christmas Day for west of the Cascades. W-SW winds.  
After Christmas - windy and wet, with Pacific storms arriving Mon and Wed Dec 26 & 28.
—> We will keep everyone informed with special statements, if all of the above comes into play
“Have the courage to let go of the things not worth sticking to."
Copyright © 1994-2022 - All Rights Reserved - The Weather Café ®

← Older Post Newer Post →