WEATHERAmerica Newsletter, Sunday, December 31, 2006 at 5:15 A.M. ET

[Larry_Cosgrove]

Great Plains Snow And Ice Storm Brings Heavy Rain To The Eastern Seaboard To Start 2007; Strength Of Heat Ridge In Florida And The Bahamas Means Above Normal Temperatures Everywhere East Of Rocky Mountains

(Disclaimer And Copyright Statements At End Of The Discussion)


WEATHER SUMMARY THROUGH NEXT 72 HOURS

The very impressive storm which has brought a variety of extreme weather to the Front Range and Great Plains will be changing character as the New Year rolls in. The snow and ice shield that has inundated much of the High Plains will break up as the low becomes a trough type system, and heavy rain with thunder will expand rapidly northeast today and tonight. As the leading edge of very warm, moist air is temporarily blocked over VA and MD on New Year's morning, secondary cyclogenesis should occur in the Delmarva Peninsula. This new low, utilizing a tight pressure gradient between it and the cP high east of NS, could produce a rapid surge of precipitation from NJ....S NY into C, E NY and New England. As the cold air may still be in place, a period of freezing rain and sleet may occur before an axis of heavy rains streak across the northern third of the Interstate 95 corridor on Monday and Monday night.

And while the Deep South, Great Plains and Intermountain Region will probably "calm down and clear out" following the departure of the storm, the Pacific Northwest will not be so lucky. Satellite views show an intense mA vortex over the Gulf of Alaska, and an equally powerful sequence of storms progressing below that gyre from near the Aleutian Islands. Strong winds and heavy rains in association with the series of impulses should reach BC....WA....OR on New Year's Day, and possibly continue through Tuesday with lowering snow elevations.


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

ISOLATED Severe Thunderstorms
(Large Hail, Microbursts, Isolated Tornadoes)
SE LA....MS....AL....FL Panhandle....W AL

STRONG WINDS (Pressure Gradient Derived)
N, C BC


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

Scattered Locations In
SE LA....MS....AL....W, C TN....AL....FL Panhandle....W GA
(QPF 1-2")


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

Scattered Locations In
N, C KS....NE
(Snow, With Sleet and Freezing Rain; 4-8")

Scattered Locations In
S MB....E ND....W MN....W IA
(Snow; 4-8")


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

Scattered Locations In
N, C QC....NL (NWF and LBR)

Isolated Locations In
AB....SK....MB....W ON


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

One of the problems this winter has been dealing with the effects of a broad cold pool over the North pole and enclosing most of the Arctic Circle. This motherlode is a symptom of a highly positive Arctic Oscillation. When a gyre of this depth and magnitude develops, teleconnections favor a rather vigorous (and at times nearly zonal) jet stream axis around 45 N Latitude. Occasionally, sub-vortices and strong shortwave swill spin up along the polar westerlies, enabling the development of impressive storms in the middle latitudes. There can even be temporary shifts to colder air in the U.S. But the persistent formation of a heat ridge in FL and the Bahamas helps to advect either ImP or mT values through a great deal of the lower 48 states. In short, having a "++AO" anomaly is not a good thing if you love harsh winter conditions.

It is apparent that some changes are in order for the 500MB longwave pattern by the end of the medium range. That said, I cannot say for sure that the eventual outcome of these deviations aloft will result in an outstanding difference in apparent weather. By Day 10 (see ECMWF comments attached), all models show a progressive jet stream configuration. While colder air is seen across the Intermountain Region and much of Canada, the presence of west-southwest flow aloft and the aforementioned subtropical high will be a deterrent to lower temperatures in locations below 45 N Latitude and to the right of the Rocky Mountains.

A strong storm is seen digging into the lower Great Plains by January 9-10, and I suspect that this feature will produce a third heavy snow and ice event from WY....CO....NM into the Upper Midwest. The abundance of deep tropical moisture may allow also for severe weather and heavy rainfall from TX and OK into the Tennessee Valley, with mainly stratiform rain in the Corn Belt. Any effect further east may be muted by the powerful ridge, and likely would not occur in Appalachia and the Atlantic Coastal Plain until some point after 240 hours.

Another impact zone to monitor is the Pacific Northwest. With ridging taking shape across the eastern Pacific Ocean, lower 500MB heights may occupy BC....WA....OR....ID after 216 hours. Moisture and cold air with cyclonic energy will combine to produce heavy rain and higher elevation snow (in fact, if the European outlook verifies snow levels could go below 500 feet).


Prepared by Meteorologist LARRY COSGROVE on
Sunday, December 31, 2006 at 5:15 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 2006 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.

[rainstorm]

thanks LC!! enjoy the new year and i look forward to more updates