WEATHERAmerica Newsletter, Thursday, February 8, 2007 at 4:50 P.M. ET

[Larry_Cosgrove]

Storm Along The West Coast Looks To Make A Big Impression Across Much Of The Lower 48 States, With Threat For First Major Snow And Ice Event In Mid-Atlantic, New England States Next Week

(Disclaimer And Copyright Statements At End Of The Discussion)

(Special Edition Dealing With Upcoming Winter Storm Threat)

WEATHER SUMMARY THROUGH NEXT 72 HOURS


Arctic air has lessened its grip, somewhat at least, across the Midwest and Northeast. The PNA-styled ridging which had allowed for the return of high pressure from northern Canada to infiltrate the U.S. is weakening. This is mostly a result of erosion from shortwaves to the north and west of the blocking signature. Smaller pools of cAk values are still present, however, and over the next seven days will play a role in conditions across the lower 48 states.

Colder readings remain in place in most of Canada and the U.S. above 35 N Latitude, and will remain locked in through Monday. But milder air can be found; evidence the warmer observations in FL and the above normal thermal profile through much of the western states. A key system to watch is the storm complex located over the Gulf of Alaska and stretching back to the International Dateline. As this series of disturbances pushes gradually southeastward, periods of rain and higher elevation snowfall will occupy most of the West by Sunday. Breakaway areas of precipitation should actually reach as far east as TX/OK (rain showers) and MO/IL/IN/KY (ice and snow) at 72 hours. This will be the first increments of the potential major winter storm to affect the nation next week.


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

STRONG WINDS (Pressure Gradient Derived)
BC....W AB....MT

STRONG WINDS (Pressure Gradient Derived)
QC


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

Isolated Locations In
N, C CA....W OR
(QPF 1-2")


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

Isolated Locations In
WA....OR....N, C CA
(Snow; Above 5000 Feet; 4-16")

Isolated Locations In
W AB....MT....W ND....W SD....NE....SW IA....NW MO
(Snow; Freezing Mist; 2-4")


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

BC....AB....SK....MB....ON....QC....NB....NS....PE I....NL

MT....NE WY....N, C NE....SD....ND....MN....IA....N MO.....N IL....N, C IN
OH....WV....N VA....DC....MD....DE....PA....NJ....NY....CT....RI ....MA....VT
NH....ME


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

When put in perspective, the upcoming threat of a major winter storm for portions of the Old South, Mid-Atlantic and New England states is all the more critical because it may be the only real shot at excessive snow and ice for those regions this winter. I say this simply because after the storm exits North America (about a week or so from now), the 500MB longwave pattern changes into a semizonal configuration. By its very nature, this type of flow regime is milder (incorporating air derived from the Pacific Ocean) and generally drier (since much of the values will flow in a downslope manner into the Great Plains and beyond), of the mP and ImP designations.

But before we see a possibly calmer, warmer trend, the first part of the medium range forecast could be termed (cautiously) "Rock and Roll" weather. While it is true that some of the numerical versions wash the storm threat out (the latest UKMET and NOGAPS outlooks as examples), three credible NWP schemes (and the entire 12z GFS ensemble package) show what could be a crippling ice and snow episode from the middle of the Great Plains into the Ohio and Tennessee Valley up through the Mid-Atlantic and New England states. the danger here is easy to see; in a very boring winter, many may be taken aback by a sudden grip of frozen precipitation and heavier snowfall. For an analogy, you can use the February storms from 1995 and 2006.

The huge Arctic anticyclone now descending from YT and N AB will be a critical player in the unfolding winter weather event. As the high passes south and east into the Mississippi Valley, the associated cold air dome will help to depress an existing from into the Gulf Coast. For this reason, when energy arrives on Days 3 and 4 and results in surface cyclogenesis, the low looks to be a bit further south than what is shown by the ECMWF and GGEM outlooks. Hence the depiction on the enclosed forecast graphic of a significant mix, ice, or snow to/from rain change area across parts of the Mid-South and into the Chesapeake and Delaware Bay vicinities. Because there is a vestigial cAk motherlode forecast to linger across parts of ON and QC, the incoming storm will likely redevelop near the VA Capes and keep the snow/ice/change line largely below the Ohio and Potomac River watersheds. This arrangement could translate to heavy snows along the Interstate 70/76 (Indianapolis IN....Columbus OH....Pittsburgh PA....Baltimore MD....Philadelphia PA) and Interstate 95 (Trenton NJ....New York NY....New Haven CT....Boston MA....Portland ME) corridors during next Tuesday and Wednesday. I should also mention that another severe weather and tornado event is a strong possibility in parts of the Deep South, including the FL Peninsula.

The low will probably incorporate the shrinking 500MB cold dome, allowing for moderate to heavy snows to linger into the Maritime Provinces into February 15. But the removal of the colder regime (and the onset of the semizonal flow aloft) will also mean milder temperatures across a good deal of the lower 48 states outside the Northeast. There are indications of a -PNA configuration (trough West, ridge East) that may promote strong warming in states along and east of the Rocky Mountains during the third week of this month.

Prepared by Meteorologist LARRY COSGROVE on
Thursday, February 8, 2007 at 4:50 P.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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[rainstorm]

i sure hope you are right about the warmth. some people are talking about a second storm right behind this one. i hope they are wrong.

[Martin]

Nice early call on this one, Larry. Seems to be panning out so far...With decent agreement amongst the models 12z this morning.

This would be over a foot of snow for portions of the mid atlantic and north east if 12z GFS verified.

[Steve]

Originally Posted by Martin

Nice early call on this one, Larry. Seems to be panning out so far...With decent agreement amongst the models 12z this morning.

This would be over a foot of snow for portions of the mid atlantic and north east if 12z GFS verified.

Seemed like the NWS in NYC gave up on it way too early. Played it down on this morning's AFD.