WEATHERAmerica Newsletter, Saturday, December 6, 2025; EXTENDED PERIOD FORECAST

[Larry Cosgrove]

EXTENDED PERIOD FORECAST

(Between Day 11 And Day 15)

 

Blocking Pattern At 500MB, Subtropical Jet Stream, James Bay Vortex Conspire To Make The Christmas Holiday Week A Memorable One!

Our Winter Love, Bill Pursell, 1963

Canadian Sunset, Hugo Winterhalter w/Eddie Heywood, 1956

Christmas Eve/Sarajevo, Trans-Siberian Orchestra, 1996

CIMMS (2)

NOHRSC (2)

WeatherBell (2)

TropicalTidbits.Com (Dr. Levi Cowan) (3)

NOAA/PMEL

NOAA/CPC

ECMWF

HPRCC/University Of Nebraska (2)

Environment Canada

WeatherBELL

I am trying to get everyone in the mood for winter weather, hence the three links to songs to start this discussion. Granted, if you only go by numerical model runs, the recent cavort from "blaster cold wave" (12z) to "major warm-up" will make weather enthusiasts dizzy (and many will go all the way to proclaiming a "Phase 8" winter disaster to a "winter cancel and warm Christmas") proclamation in the space of about 6 hours! It is ludicrous, and reminds me that one should always aim for a middle ground when numerical models show unstable behavior. In this case, I am sold on something of a warm-up in the 6-10 day period followed by a grinding avalanche of Arctic air east of the Rocky Mountains in the 11-15 and 16-20 day time frames. Keep in mind that the snowpack is becoming quite thick, which may alter and enhance Arctic intrusions into the lower 48 states.

Most of the model guidance for the end of the month through much of January favors an -EPO/-AO signature with a significant cold-drain trough complex over the East. What is difficult is timing the exit of the warming trend out of Texas and the Great Plains shown on the ECMWF model suite. The American and Canadian members keep the Great Lakes and New England/Mid-Atlantic cool, implying maybe a day or two of warmth before an Arctic front crashes the party just before Christmas. The southern branch has a storm which could start a drain of the cAk air mass down the Great Plains and Texas, then pushing rapidly through the Mississippi Valley, then the Appalachian Mountains. This is consistent with analogs and model guidance, and may take the worst of the Arctic values through the   central and eastern chambers of North America. The disturbance may create problems with snow and ice in the run-up to the holiday week, and must be watched as it moves out of the western Gulf of Mexico.

There is more talk about stratospheric warming and splitting (see 10MB maps). Always keep in mind that any surface impacts are 2 to 4 weeks after the episode, which might indicate a cold-dominated January. But when looking into next month, always factor in a climatology-favored "January Thaw" in the middle of the time frame. The analog-derived prediction shows a James Bay cAk 500MB vortex, which can create interesting options for snow and ice.

 

Prepared by Meteorologist LARRY COSGROVE on 
Sunday, December 7, 2025, 2025 at 1:45 P.M. CT

Disclaimer: 
The previous statements are my opinions only, and should not be construed as definitive fact. Links provided on this newsletter are not affiliated with WEATHERAmerica and the publisher is not responsible for content posted or associated with those sites.

Copyright 2025 by Larry Cosgrove

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