MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
Modest Storm Threat For Dixie, Appalachia And Eastern Seaboard On February 12 - 14
The European model is not entirely sold on the threat for a frozen precipitation event across portions of Appalachia and the Mid-Atlantic region at midweek. The upper shortwave seems strong enough on the operational ECMWF panels, so perhaps this time the GFS and GGEM equations will provide the correct forecast of wintry precipitation? Locally heavy rain will move from the Gulf Coast into the Southeast, with some potential for snow and sleet emerging in N AL, NW GA, E TN, W NC, W VA, E KY, WV into MD, PA, NJ. Keep in mind that the numerical models show no high-latitude blocking (nice -EO ridge complex however), with colder air largely situated over the western and northern states into the weekend.
....Followed By Great Lakes Disturbance And A Rather Strong Arctic Intrusion On The Weekend!
Plymouth State University Weather Server (3)
Even in this progressive 500MB longwave pattern, cold air will be reaching into the U.S. from time to time. There is good consensus among the computer schemes on a truly massive surge of Arctic air into the eastern half of the nation this weekend. There are hints from the ensemble members of all three models of an important winter-type storm moving from Texas and Louisiana into the lower Great Lakes and then Laurentian Shield in the Friday to Sunday time frame.
The ECMWF version is still somewhat gun-shy about allowing the colder elements to shift into the eastern third of the U.S., and I suspect that cold impacts over the Deep South and Eastern Seaboard below 40 N Latitude will be minimal. A new disturbance may reach the West Coast (Oregon and California) on February 19 - 20, and that system could be a cold air advection mechanism into the West during the last week of February.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
ESRL : PSD : CDC Interactive Plotting and Analysis Pages
Shift In 500MB Longwave Pattern Keeps Coldest Air In Western 2/3 Of U.S.; Dixie And The East Coast Trend Warmer (And Probably Wetter As Well)
University Of Nebraska/HPRCC
Pennsylvania State University E-Wall
Rule 1 of winter season forecasting: with no high-latitude blocking, no extensive and long-lasting cold and snow is likely to occur anywhere in the lower 48 states.
This line of thinking works well in review of the past two months. There have been regional extreme winter weather events (case in point the New England blizzard on Friday and Saturday), but no truly national cases of widespread snow, ice and cold air. Arctic intrusions have largely been transient. Despite constant chatter in the weather community about "stratospheric warming events" and "favorable MJO phases" (both phenomena are difficult to predict to begin with, and impacts from each are not at all well understood), the first week of February has seen cold air and snowfall largely limited to the Great Lakes and Northeast (sometimes including the Ohio Valley into the Mid-Atlantic region). And despite the constant drone of "winter returns" by the ever-unreliable GFS model series, it does not look like February will end up on the cold and snowy side of the seasonal ledger.
Purely neutral ENSO episodes are known for volatility, occasional cases for intense storms and little fixation of cold intrusions into specific portions of the U.S. If you live in the West, you will recall that some of the coldest temperatures of the new century have occurred this winter, only to be followed by ridiculous turnabouts to warmth and dryness. The Dixie, Appalachian and Eastern Seaboard states have noticed the re-appearance of a flat subtropical high over Cuba and Florida ahead of each storm advancing from the West, which has resulted in sudden boosts in readings that effectively eliminate short-lived cold spells from the monthly averages.
To be honest, I do not see much change in this pattern during the 11 - 15 day period. I can see no cases for high-latitude blocking ridges (aside from occasional signals of positive height anomalies in Greenland or northern Canada, which may result in a two to three day cold spell east of the Mississippi River). Rather, with a positive tilt trough covering the western two-thirds of the U.S., the coldest air will likely be over the Desert and Intermountain Regions. An active storm track should provide threats for severe weather and/or heavy rain across the Old South into the Northeast. Snow potential will still likely occur from the western mountain ranges through the High Plains into the Upper Midwest. But I cannot even promise that Chicago IL will see a healthy snow episode.
We are running out of time for the winter season of 2012-2013 do make any kind of turn-about. One bright spot for snow and cold enthusiast was the New England blizzard, and it is not an impossibility that a lower latitude snowfall threat could emerge elsewhere in the country. But southwest flow in the upper atmosphere, and increased ridge presence over Cuba and Florida and lack of linkage from tropical forcing in the central equatorial Pacific Ocean tells me that the CFS monthly projection for March (very warm southern and eastern sections) is likely to verify.
And that's the way it is.
Prepared by Meteorologist LARRY COSGROVE on
Saturday, February 9, 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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