MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
After A Brush With Winter Over The Northeast, It’s Beginning To Look A Lot Like….SPRING?
Plymouth State University Weather Server (2)
Let me say right off the bat that I am not 100 percent sold on the prospect of important snow and/or ice in Appalachia and the Northeast by midweek. Yes, there will be a 500MB shortwave moving out of Texas, and the cPk/mT frontal structure will provide some potential for wave cyclogenesis. If a low pressure area does take shape in central North Carolina on Tuesday night, the weak character of the system and lack of strong vertical motion implies that the best threat for frozen precipitation would be in east-facing higher elevations and above the Mason-Dixon Line, exiting the northeastern states on Wednesday night.
Gulf Of Alaska Low Dominates U.S. Weather Pattern At Least Through December 4
There it is…again! The Gulf of Alaska Low, often the bane of those wanting to see the lower 48 states turned into a winter wonderland, remains in play on most of the computer models through at least December 4. Yes, there have been cases in history where a strong negative 500MB height anomaly in this position is supportive of Arctic intrusions and significant ice and snow events (1976-77 and 2003-04 readily come to mind). But, as is shown in the 12z Nov 24 ECMWF model run, the mA vortex to the left of WA and BC occurs with no real high-latitude blocking near North America (yes, the various ensemble groups were incorrect over the past ten days….). Bottom line here is simple: do not count on ANY impressive cold, snow, or ice scenarios in the U.S. through the medium range.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
After Two Weeks Of Poor Verification From The Numerical Models, Will North America REALLY See A -AO/-NAO Blocking Signature With Storms And Cold Air For The U.S.?
University Of Illinois
University Of Nebraska/HPCC
Pennsylvania State University E-Wall
As someone who appreciates a good snow or ice storm, I will admit to some sense of depression this past week. After all, the computer models (especially the respective ensemble packages) have been tooting the horn loudly for widespread -WPO/-AO/-NAO blocking within the Arctic Circle. Since this has happened in October and in parts of November, it was not at all unreasonable to go with that scenario, and its attendant warm West/cold East pattern in apparent weather. But over the past few days, the portrait of an impressive Baffin Island/Greenland Rex signature has faded before the reality of a strong Gulf of Alaska Low and semizonal jet stream configuration. In other words, mild and dry conditions outside of the Great Lakes and Northeast.
But I suspect that the numerical models are on to something with a return to high-latitude blocking in December, if only in an erratic fashion. The 250MB vector wind verification for North America in November has been decidedly in favor of a deep eastern U.S. trough, and the surface temperature skew has been similar to neutral/positive cold seasons such as 1960-61, 1993-94, and 2003-04. I have seen nothing which would dissuade me from a “2/3 cold” winter pattern. But a caveat should be employed: the NAEFS and CFS long term forecast equations are VERY warm, with the American format at vast odds with its ECMWF weekly prediction counterpart (which is showing huge up and down temperature swings through week three of December).
If the pattern DOES break in the 11 – 15 day period, it will likely be from a large southern branch storm emerging from the tropical Pacific Ocean and moving along the Gulf Coast and Eastern Seaboard (I am thinking December 7 – 9). Similar to the current oceanic/Newfoundland monster, this feature would at once pump up the blocking ridge in the -NAO and -AO positions, while helping to extend the vast northern snow cover across the Midwest and closer to the East Coast. If this feature keeps showing up in the variant series of the GFS, GGEM, and ECMWF schemes, then “real” winter will pay a visit to most of the U.S. as we start the second week of December.
Keep your fingers crossed, snow lovers!
Prepared by Meteorologist LARRY COSGROVE on
Saturday, November 24, 2012 at 6:30 P.M. CT
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 2012 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.