WEATHERAmerica Newsletter, Sunday, February 25, 2007 at 4:55 A.M. ET

[Larry_Cosgrove]

East Coast Gets Snow, Slush, And Rain As Another Massive Storm Impacts Western States With Heavy Precipitation; 500MB Blocking Pattern Keeps Winter Across Midwest And Northeast, But Dixie And Lower Ohio Valley Likely To See Another Severe Thunderstorm Event This Weekend

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WEATHER SUMMARY THROUGH NEXT 72 HOURS


The extremes are in control over the coasts, while the middle of the continent is quiet. For now, at least....

The disturbance moving into the Pacific Northwest is notable for two reasons. One is the increasingly wet, cold regime settling in to the left of the Front Range. Torrential rains along coastal sections may give way to showers and thunderstorms, with much of the CA Central Valley seeing a flood threat later today into Monday. The chill mPk regime will support snow as low as 3000 feet, and the slow progression of the longwave low toward the Great Salt Lake should make travel on major Interstate highways a debacle through Day 3. 500MB height falls will bring destabilization into the southwestern states as well, and enough upper dynamic support is present for convection in S CA....S NV....AZ....NM over the duration of the short range.

A vast upper level low in the vicinity of the Great Lakes is the same system responsible for widespread thunderstorm activity in the lower Great Plains and Mississippi Valley during the previous 24 hours. Now in occlusion, the overrunning sector of the low will give rise to secondary cyclogenesis near the VA Capes by later today. Disorganized bands of snow, sleet, and rain (mostly south of the Mason-Dixon line) will tend to cluster and expand tonight over CT....S NY....and NJ, with snow and ice dominant north of an Easton PA....Fords NJ....Great Neck LI NY arc. Snowfall amounts of as high as 6 inches (below Interstate 84 and 90) may occur before the system exits east of Nantucket MA on Monday morning. Of course, the truly heavy snow and ice pattern occurs today in parts of WI and MI, but this should fall apart tonight, followed by a broad area of drizzle and lighter snow shower activity in the Corn Belt.

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

ISOLATED Severe Thunderstorms
(Microbursts, Large Hail, Isolated Tornadoes)
FL Panhandle....E AL....GA....SC....NC....VA


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


Scattered Locations In
FL Panhandle....E AL....GA....SC....NC....VA....DC....MD....WV....E KY....C, E TN
(QPF 1-2")

Scattered Locations In
Coastal BC....W WA....W, C OR....N, C CA
(QPF 1-3")


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

Isolated Locations In
PA....N, C NJ....NY
(Snow, With Sleet, Rain; 1-3" Before 12 Midnight)

Scattered Locations In
WI....MI....ON Peninsula
(Snow; With Sleet And Freezing Rain C Lower MI; 4-12")

Scattered Locations In
N, C CA....OR....WA....BC....ID....N UT....N NV
(Snow; Above 3000 Feet; 4-24")

Scattered Locations In
NL/LBR
(Snow; 4-12"; Blizzard)


COLD TEMPERATURES OUTLOOK
(potential of daily maxima staying below 32 deg F/0 deg C; blue shading indicates dangerous wind chills)

OR....WA....BC....AB....SK....MB....ON....QC....NB ....NS....PEI....NL
E MT....ND....MN....WI....MI
NY....N CT....MA....VT....NH....ME

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

With the Rex block over Hudson Bay apparently holding through Day 10, it would appear that winter is not done by any means. There is still the matter of a subtropical high over the Greater Antilles, which sooner or later will begin to have a huge impact on temperatures in the U.S. (since we have a budding La Nina anomaly in the equatorial Pacific Basin). But for now at least, the prominence of the Canadian blocking signature suggest that temperature trends during the longer term will be colder.

And stormy too. The remnants of the current storm will lodge as a mean 500MB trough in the Great Plains and Midwest, just below the block in central Canada. By Day 4, the storm now coming into the West Coast will emerge over the NM Front Range, in the process dumping heavy snowfall through a good portion of the Intermountain Region. This disturbance will begin to merge with the older trough complex and phase with a second component, the subtropical jet stream, creating a huge cyclone that looks to rip the south central U.S. and lower Ohio Valley with severe thunderstorms and tornadoes while delivering a devastating snow and ice event across the central Missouri Valley into the western Great Lakes. Since a cA regime with high pressure looks to straddle QC, I am following the 0z Feb 25 UKMET and ECMWF model scenario of redevelopment near Cape Hatteras NC, with a long, and potentially ugly period of snowfall and mixed types in the Mid-Atlantic and New England regions (with considerable wind again) by the start of the weekend.

Next week there may be an easing of the blocking configuration, with many of the numerical models and the respective ensemble members showing a semizonal flow through the lower 48 states. So where much of the U.S. and Canada see moderation in temperatures and reduced risk of precipitation, the Pacific Northwest looks to stay raw with perhaps another heavy rain and snow situation at 240 hours.

Prepared by Meteorologist LARRY COSGROVE on
Sunday, February 25, 2007 at 4:55 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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