WEATHERAmerica Newsletter, Sunday, January 28, 2007 at 3:55 A.M. ET

[Larry_Cosgrove]

You Wanted Colder And Stormier, Well You Got It! Vast Area Of Arctic Air Forecast To Dominate Much Of U.S. And Canada Through Next 10 Days (But Watch Out For That Stubborn Heat Ridge Over The Greater Antilles)

(Disclaimer And Copyright Statements At End Of The Discussion)

WEATHER SUMMARY THROUGH NEXT 72 HOURS


True to form, the shot of bitter cold air which passed from the Great Lakes through the Northeast did not last. Enough warm advection occurred to allow for all rain in much of the Mid-Atlantic and New England states last night, and as cold air returns later today, the atmosphere will be too dry to support much, if any, frozen precipitation. That said, there IS another disturbance and cold pool dropping out of the Corn Belt into the Carolinas, which may have enough dynamics associated with it to offer some lake-related or orographic snowfall in the lower Great Lakes and Appalachian Mountains. Most importantly, this system will energize another oceanic storm which could reach NL/NWF by &2 hours with strong winds and heavy snow. Yet another impulse lurks upstream in the Prairie Provinces which could have the same snow shower and squall developing capacity in parts of the Midwest into the Eastern Seaboard tomorrow and Tuesday.

Speaking of the cold air, there is a fairly impressive bank of cAk values across Canada into the Upper Midwest. Ridging over BC and WA will build into AK and YT by Day 3, enabling shortwaves in the Arctic jet stream to dig southeastward. This is a critical issue because of a diffuse upper low covering the southwestern U.S. Areas of rain in CA may expand eastward into colder values over the Intermountain Region, thus enabling the development of snow across UT, N AZ, N NM and CO. As the northern stream impulses begin to kick/scour out energy from the lower Colorado Valley, surface cyclogenesis will get underway in S TX along the leading edge of IcA values. Rain that organizes in the Lone Star State could have a significant impact on apparent weather throughout the Old South, Appalachia, and the Atlantic Coastal Plain around Days 4 through 6 (see MEDIUM RANGE OUTLOOK below).

SEVERE WEATHER OUTLOOK
(potential for tornadoes, damaging winds, and large hail within the next 24 hours)

STRONG WINDS (Pressure Gradient Derived)
WV....W VA....W NC....W SC....N GA....E TN....E KY


HEAVY RAINFALL OUTLOOK
(potential for an inch or more total rainfall within the next 24 hours)

Isolated Locations In
C, S CA
(QPF 1-2")


WINTER WEATHER OUTLOOK
(potential for 2-4 inches or more of snow, or significant ice/glazing)

Isolated Locations In
E ON....W NY....W PA....WV....W VA....W NC....E TN....E KY....OH....Lower MI....N IN
(Snow; In Squalls; 2-4")


COLD TEMPERATURES OUTLOOK
(potential of daily maxima staying below 32 deg F/0 deg C)

E AB....E MT....SK....ND....N SD....MN....ON....MI....WI....N, C IA....IL....IN....OH....KY
WV....KY....TN....W NC....W VA....W MD....W, C PA....W, C NY....VT....NH....QC....N NB
PEI....NL
MEDIUM RANGE OUTLOOK
(weather trends through the next 6 to 10 days)

After a seemingly endless series of days with mild temperatures throughout much of the Northern Hemisphere, cold air and snow cover are making advances in North America and Eurasia. That said, the 500MB longwave pattern is still not extreme for late January and early February, and we must wait for the development of a strong +PNA signature (a thumb projection block) for truly brutal cold to ooze into the lower 48 states.

There is reason to believe that the colder, more energetic ECMWF and GGEM schemes are correct (but please realize that the dual blocking configuration shown by the Canadian model is a far outlier). One issue is placement of the ridge axis in the West, which has tended to be to the right of earlier computer model depictions. This slight error may translate to the colder air advancing farther south and east, with concurrent suppression of the heat ridge enveloping the Greater Antilles. If the subtropical high is forced into the Sargasso Sea and Leeward Islands, then moisture will flow into developing storms without significant warm advection.

Following this line or reasoning, the broad, diffuse upper low now in CA will be forced out into the lower Great Plains this week as shortwave energy in the Arctic jet stream acts in a kick/phase capacity. While there is basic agreement among the numerical versions on the place of cyclogenesis (S TX), the latest GFS insists on taking the low center into the Ohio Valley, perhaps with a secondary cyclone in the VA Capes around 144 hours. That possibility exists, and would mean a mainly rain scenario for many communities in the Ohio Valley, Mid-Atlantic and southern New England regions. But if you look at the depth of the cold air, which is impressive with a huge cAk motherlode centered roughly near James Bay in about 5 or 6 days from now, a sound argument for suppression and redevelopment exists. And with it the strong possibility of a significant snow and ice episode stretching from the Red River Valley of TX/OK into the fabled Interstate 95 corridor of the Northeast.

There is ample evidence from NWP model and ensemble forecasts of a continued, though somewhat weaker, +PNA/-EPO ridge presence through Day 10 and beyond. This would allow for cold air to continue in place through the northern two-thirds of the U.S. and most of Canada. There might also be a chance for another Gulf Coaster/Hatteras low formation at some point.

All of you snow lovers feel better now?

Prepared by Meteorologist LARRY COSGROVE on
Sunday, January 28, 2007 at 3:55 A.M. ET

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 2007 by Larry Cosgrove

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