MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
Broad, Brutally Cold Arctic Vortex Over Hudson Bay Keeps Midwest And Northeast In The Icebox....
I will repeat that the coldest air of the winter season will visit the Midwest, Mid-South and Eastern Seaboard between January 31 and February 4. One complication of the cold air intrusion will be that the frontal structure may undergo wave cyclogenesis over Appalachia on Wednesday night and Thursday (you can make out the related shortwave exiting TN and GA on the ECMWF panels). With warm air lingering aloft, I could easily see a sleet/freezing rain to snow event setting up from C, E TN through the interior of the Mid-Atlantic and New England regions. Heavy rain and some thunder may occur along the Atlantic Coastal Plain before the cold and dry air mass arrives on Thursday night.
....But Lack Of Blocking At High Latitudes Allows For Mild Air Across The West And Dixie
Plymouth State University Weather Server (3)
While the Midwest and Northeast will turn extremely cold again, you cannot help but notice the lack of pronounced high-latitude blocking in the forecast charts through the next two weeks. The cold plumes are being driven by an extremely large, somewhat displaced circumpolar vortex that will find a home in the vicinity of James Bay. A newer "replenishing Arctic air mass and shortwave will enter the picture on February 3 - 4, and that could mean some significant snow, ice and rain chances for the Midwest and Northeast. Most importantly, the lack of amplitude to the shortwaves, even those which are intense, should allow the West, lower Great Plains and Dixie states to largely miss out on the very cold temperatures through the 6 - 10 day period.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
No Big Pattern Changes Just Yet; Broad Cold Pool Centered Over Hudson Bay May Join Forces With Active Southern Branch Jet Stream For Another Round Of Wintry Precipitation And Cold Temperatures (Mainly East Of The Continental Divide)
University Of Nebraska HPRCC
Pennsylvania State University E-Wall
The monster storm sweeping across the northern Atlantic Ocean may be a harbinger of "things to come". The immense gyre is actually pulling the circumpolar vortex out of Canada, if only temporarily. The lifting out of the cAk motherlode is part of the reason why the eastern two-thirds of the U.S. will be seeing a 2 - 3 day warming trend in the near term. Keep in mind that when you look at the northern Pacific Ocean satellite views, you will see a "mirror reflection" type storm in the vicinity of Japan. It is my opinion that at some point between now and February 21, another conjunction of the Arctic vortex and a mid-latitude cyclone will occur, somewhere in between what is seen now. And yes, if you do the math of latitude and longitude along with following trends in 500MB anomalies, that would seem to imply the threat for a major tempest in an arc from northern Mexico into the Mid-South and the northeastern U.S.
If that sounds like a "gloom and doom" scenario, consider that the ensemble packages of the major numerical models present (once again) a vast dome of Arctic air which keeps digging into the Midwest and Northeast. We have seen this winter a preponderance of cold, albeit transient, disturbances drop through California into northern Mexico, with the impulses recurving to the northeast in a variety of ways. This is NOT related to the Madden-Julian Oscillation (which, while flaring, has NOT shown strong and durable linkage to the polar westerlies, hence no long-lasting blocking signatures) and has nothing to do with "stratospheric warming" (where have all those outlooks for bitter cold across most of the nation gone, huh?). Rather it is a "chance scenario" where vigorous shortwaves amplify and hook up with the field of vorticity and cold air which seems to making a home for itself over Hudson Bay.
This set-up may unveil itself in the 11- 15 or 16 - 20 day forecast periods. I would not be surprised if another decent warm spell gets going across the Dixie states. But if you follow a blend of the NAEFS super ensemble and CFS February predictions, there are still chances for impressive cold air advection above 35 N Latitude. I suspect that when winter DOES end, it will be from a familiar source: ridging across the Greater Antilles which "bubbles up" and advances across the Gulf Coast and Southeast, with an eventual expansion with southwest flow through the Ohio Valley and Mid-Atlantic regions.
But in this neutral ENSO pattern, volatility will be the concern. The West may get another cold surge and storm around February 7, with that disturbance riding along the underside of the colder values which I believe will occupy the Midwest and Northeast (yes, I am following the ECMWF ensemble group with that idea). IF the impulse phases with the Arctic motherlode situated over Ontario and Quebec, we may see a major winter weather event from the Tennessee and Ohio Valleys through Appalachia into the northern end of the Interstate 95 corridor. That precipitation event might then be followed by a short-term, biting cold intrusion which gets into the Deep South before retreating around February 11 - 12.
Oh, the possibilities!
Prepared by Meteorologist LARRY COSGROVE on
Saturday, January 26, 2013 at 7:30 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
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