WEATHERAmerica Newsletter, Sunday, January 21, 2007 at 5:10 A.M. ET

[Larry_Cosgrove]

Disturbance Over Dixie, Ohio Valley Will Break Up By Tomorrow; Transient Cold Shots Across Midwest, Northeast Through January 30 May Be Followed By Massive Winter Storm And Impressive Intrusion Of Arctic Air

(Disclaimer And Copyright Statements At End Of The Discussion)

WEATHER SUMMARY THROUGH NEXT 72 HOURS


Yes, it is colder across the Great Lakes and Northeast. But considering the calendar date, that is a normal situation and the temperatures are not in the extreme range. The flow aloft is west-southwest, a balance between an AO-styled motherlode over northern Hudson Bay and a persistent heat ridge over Cuba and the Bahamas. And while a system which brought locally heavy snowfall to parts of the Great Plains is ejecting out into the Ohio Valley, the warming profile of the atmosphere with a confluent pattern says that this feature will get sheared apart with relatively minor precipitation concerns. Heavy rain and locally strong thunderstorms in Dixie will fade from view tomorrow, with snow amounts dwindling to flurries and snow showers in the Mid-Atlantic and New England states. The rain/snow transition during this process may actually reach S NY, CT, and RI before the entire area of moisture disperses.

Very cold temperature continue to be felt in the southwestern states, courtesy of a cold intrusion and upper low that is expected to remain in place near the AZ/NM border with Mexico through the following 72 hours. Some moderation is likely to take place west of the Colorado River, but other parts of the normally mild deserts could stay rather chilly. In fact, orographic action in response to the low aloft could bring generous snows as far south as Tucson AZ and Las Cruces NM in the near term.

Another cA-based shortwave (with a short-lived burst of very cold air) is progressing southeastward from AB, SK, and MB. AS this system sweeps into the Upper Midwest and Great Lakes, it could tap into energy and moisture from the disturbed area in the Desert Southwest. So some snow and ice could develop from the northern Mississippi Valley into IN....OH....KY on Monday night and Tuesday. Clouds from overrunning inspired by the complex feature could also overspread much of the Old South by January 23.

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

Some Thunderstorms May APPROACH Severe Limits
SE LA....S MS....C, S AL....FL Panhandle....SW GA

Some Thunderstorms May APPROACH Severe Limits
S AZ....S NM....extreme W TX

STRONG WINDS (Pressure Gradient Derived)
C BC

STRONG WINDS (Pressure Gradient Derived)
C, S NV

STRONG WINDS (Pressure Gradient Derived)
NL/LBR....extreme E QC....NB....PEI....NS


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

Isolated Locations In
C, E MS....AL....FL Panhandle....W GA....C, E TN
(QPF 1-2")

Scattered Locations In
Coastal AK Panhandle, BC
(QPF 1-3")


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

Scattered Locations In
C, S AZ
(Snow; Above 4000 Feet; 4-12")

Isolated Locations In
CO....WY
(Snow; 4-8")

Isolated Locations In
S WI....N IL....NW IN....SW Lower MI
(Snow; 2-4")

Scattered Locations In
AK Panhandle....W, C BC
(Snow; Above 3000 Feet; 4-16")


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

Scattered Locations In
E WA....E OR....NV....CA Deserts....AZ....W, C NM....CO....WY....UT....ID....BC....AB....MT
SK....MB....ND....SD....NE....N KS....NW MO....IA....MN....ON....MI....WI....N IL....N IN
extreme N OH....extreme N PA....NY....N CT....N RI....W, C MA....VT....NH....ME....QC
NB....NS....PEI....NL


MEDIUM RANGE OUTLOOK
(weather trends through the next 6 to 10 days)

If you look at the satellite image of the Pacific Basin (attached) and current 500MB charts, you can see easily why there are no really impressive storms. And also the reason that any cold intrusion into the U.S. is essentially transient, and not at all extreme. Earlier promises of massive EPO or PNA styled ridging have not verified; if you do not believe, then why is that huge storm in the Gulf of Alaska with a fast zonal flow originating all the way back in China? If we see a truly strong series of height rises with block formation into N BC, YT or NT, then the unique drainage of cAk values and upper shortwaves will follow. The energy would then scoop out a vestigial disturbance lingering near the coast of CA, interact with the ever-potent subtropical jet stream. And the cold air plunge would be more than satisfying to those enthusiasts wishing on a visit from Old Man Winter.

But "set-up" is NOT present for Day 4, when a fairly vigorous 500MB impulse scoots across the Great Lakes and a concurrent disturbance rides through Dixie. The northern system will bring some significant snow squall activity to the Midwest and Northeast, in a manner similar to the event seen this past Friday and Saturday. Meanwhile, a weak low moving along the Gulf Coast and then following the western rim of the Gulf Stream will bring primarily rain to much of the Old South (with some concerns for mixed or freezing types in N TN....KY....WV....VA....W, C NC). These two feature will merge far to the east of New England and undergo bombogenesis around Day 5, with the result being possible blizzard conditions in portions of the Maritime Provinces and NL/NWF. Another shortwave moving south of a cAk vortex in QC will promote some warm advection in the Corn Belt and Mid-Atlantic regions in the 144-192 hour time frame.

Then the fun begins. Or at least possibly begins. A closed low is forecast to take shape between the Aleutian Islands and HI around January 29, with the cold gyre pumping up atmospheric heights from WA into E AK and YT. High velocity winds and impulses seen now in the vicinity of Japan and Korea will be forced southeastward, deepening the persistent upper level low near CA. At the same time, Arctic stream shortwaves will drop southeastward. One piece of energy should race into the Great Lakes and then New England, drawing in very cold values from the interior of Canada and enhancing a developing baroclinic zone from TX into coastal NC. Another disturbance may progress along the eastern rim of the Rocky Mountains, drawing out the aforementioned closed low to its west. By 240 hours, surface cyclogenesis should get underway in the western Gulf of Mexico.

It is too early to say what kind of track this new storm will take, and obviously it would be ill-advised to predict any direct aspect of apparent weather. But this much appears likely: widespread cold air across much of the nation excepting the FL Peninsula. This siege of cA type temperatures will prove troublesome for the Southwest, already suffering crop losses from record low readings. And with some suppression of the infamous heat ridge over the Greater Antilles (which is still there, and likely to be present at the end of the medium range), odds would favor a significant winter storm progressing through the Deep South and intensifying along or east of the Atlantic Coastal Plain.

Fluff up your pillow, and dream...

Prepared by Meteorologist LARRY COSGROVE on
Sunday, January 21, 2007 at 5:10 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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