WEATHERAmerica Newsletter; Saturday, December 21, 2024; EXTENDED PERIOD FORECAST

[Larry Cosgrove]

EXTENDED PERIOD FORECAST

(Between Day 11 And Day 15)

 

The Winter Weather That You Have Been Waiting For?

CIMSS (2)

NOHRSC (2)

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

NOAA/PMEL

NOAA/CPC

IRI/Columbia University

HPRCC/University Of Nebraska (2)

Environment Canada

ECMWF (3)

TropicalTidbits.Com (Dr. Levi Cowan) (6)

There are telltale signs that this developing winter will not be a total loss for snow lovers and cold enthusiasts. Mind you, it is highly unlikely that a truly extreme bitter/ snowy/icy season like the late 1970s or the 2013-14, 2014-15 debacles will occur. Global warming is real and has had an impact on the past ten years on conditions east of the Rocky Mountains, and changes in sea surface and upper atmospheric patterns have told me to always add a few degrees to forecast outcomes in order to assure verification. After all, when was the last time you saw temperatures go below zero in Central Park (NYC) or snowfall in South Florida? But conditions seem to favor some turnabout. And we can start with the very obvious storm threat in the Mid-Atlantic and New England in the first week of January.

I have been telling clients and friends alike for about a week now that the predicted "blowtorch" would be like the rest of the big warm-ups predicted since Thanksgiving: quicker, less emphatic and likely not having as strong an impact as what the model guidance suggests. To be sure, once the current transient Arctic regime moves out of the eastern third of the lower 48 states, a notable warm-up will occur. But by New Year's Eve, the "dominoes" will be set up to fall, with likely blocking ridge formation in a -EPO/-AO/-NAO configuration. As in "Alaska/Arctic Canada/Greenland. There is near-complete agreement on this scenario from NWP and analog resources, so confidence is growing on winter returning with a vengeance during the first week-and-a-half of 2025.

Speaking of analogs, I have not changed my comparison years. The presence of a strong subtropical jet stream feeding of a far-west Madden-Julian Oscillation (Phases 2,3,4) will mean increased precipitation chances for Texas and Dixie into the Mid-Atlantic, and possibly New England into the Maritime Provinces as well. Pronounced warm advection into the high latitudes will favor Arctic and polar branches southward, and could create a phasing scenario somewhere between Cape Hatteras NC and the MA Islands. Those of you familiar with winter season climatology will quickly realize this is a "snow track" from the Potomac River into Bay Of Fundy. But I cannot rule out some rain involvement for the Interstate 95 corridor, given the time distance and the fact that air and water temperature measures are vague this far out. Keep in mind that the snow cover in Canada and the Great Lakes is quite impressive, so if a strong enough ridge developed about the North Pole, clear skies and night radiation off of the snowpack implies quick formation/expansion/advection into the lower 48 states, especially to the right of the Continental Divide. "January Thaw" climatology with a negative ENSO (moderate La Nina) suggests January 12 - 22 as the "melting antidote". The last week of January and first of February should return the cold and frozen precipitation chances.

Now for those of you who love heat and tropical systems, most guidance is saying that "summer in spring" is on tap for the Southwest and south central USA in March. Finally....I have some exciting weather to describe

 

Prepared by Meteorologist LARRY COSGROVE on 
Saturday, December 21, 2024 at 11:55 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 2024 by Larry Cosgrove

All rights reserved.
This publication may not be reproduced or redistributed in whole or in part without the expressed written consent of the author.