WEATHERAmerica Newsletter, Thursday, January 10, 2008

[Larry_Cosgrove]

WEATHER HAZARDS (During The Next 24 Hours)

SEVERE WEATHER OUTLOOK
(potential for tornadoes, damaging winds, and large hail within the next 24 hours)
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
Coastal BC, WA, OR
(QPF 1 - 2")

Isolated Locations In
FL....Coastal GA, SC, NC, VA....E MD....DE....NJ....E PA....SE NY....CT....RI....MA
SE NH....E ME....NB....NS
(QPF 1 - 2")


FROZEN PRECIPITATION OUTLOOK
(potential for accumulation of ice rime, freezing rain, sleet or more than 3" total snowfall within the next 24 hours)

Scattered Locations In
N, C NY....W MA....VT....NH....W, C ME....N NB....QC Eastern Townships
(Mix or Change to Glaze; 1/4" Ice and up to 4" Snow)

Scattered Locations In
C ON....C QC
(Snow; Blizzard; 4 - 12")

Isolated Locations In
W ON....Upper MI....N WI....W Lower MI....N IN....N OH....NW PA....ON Peninsula
(Snow; In Squalls; 4 - 12")

Isolated Locations In
BC....WA....OR....ID....N UT....W CO....W WY....W MT
(Snow; 4 - 12")

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)


Colder Air Returns To The Lower 48 States

Despite what you may here from some sources about the "lack of cold air", Arctic values have appeared fairly often over Canada this winter. Drainage into the U.S. has been rare, of course, but the build-ups of cAk regime have appeared. Such is the case in the near term; note the abundant field of subzero readings across the northern latitudes. Some of the colder realm will drift south in the near term, in concert with a trough moving through the Mississippi Valley and generating a storm along the Eastern Seaboard. This is not the worst of the tundra values, of course (which WILL head south in the medium range). But the presence of these lower numbers should give a hint at "things to come" during the days ahead.

Diffuse Disturbance Over The Pacific Northwest Will Bring Snow To Locations Further East


Although the spread-out storm complex over the Pacific Northwest does not (now) look the least bit impressive, the energy associated with this feature will give rise to an important winter storm along the East Coast within 72 hours. Linking with the strong subtropical jet stream seen on GOES images (stretching from HI into the Deep South), this feature will grow into a compact storm with sufficient energy and cold air to create snow and ice related problems for much of Appalachia and the Interstate 95 corridor north of Richmond VA. Mixture with sleet and rain (or changes to freezing rain) could curtail snow impacts along the immediate coast, but accumulations of up to a foot may occur just north and west of a Fredericksburg VA to Lynn MA line this Sunday into Monday. The disturbance, once it intensifies, will be the catalyst for mean trough formation and drainage of colder air into the U.S. next week.

Warmth Lingers Only Over The Southwest And The Florida Peninsula

While it is true that the main push of Arctic values into the U.S. will not occur until next week, the thermal profile during the near term is actually quite chilly, with warmer air limited to parts of the American Southwest and the Florida Peninsula. This arrangement of temperatures will favor a storm formation and track from the Southeast up the Atlantic Coastline by late in the weekend.


MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)


Arctic Motherlode To Visit The Great Lakes....

A look at the numerical models for the past two runs (12z and 18z) shows a 500MB longwave pattern that has been distinctly rare over the past 11 years: an Arctic motherlode depressed into the Great Lakes with a vigorous -EPO signature and signs (from the 12z Jan 10 ECMWF version) of a developing -NAO styled positive height anomaly. Even if the cAk gyre assumes the position shown in the 18z GFS operational depiction (over Ontario), the push of colder values would be impressive. In short, those who wrote off the 2007-2008 winter as "one of the warmest ever" will, for the moment at least, be very disappointed.

....With Widespread Extreme Cold East Of Continental Divide!

The core of the bitter cold air will fall into the mean trough over North America, with the worst of the bitter air mass lying between the Continental Divide and Appalachian Mountains. Since the actual core of the cAk dome will pass through the Upper Midwest and Great Lakes, a relatively rare event, the worst part of the severe temperature drop will be felt on the U.S. side of the border. It is conceivable that if the operational European and American scenarios are correct, that the nocturnal surface 0 deg F isotherm could reach as far south as an Interstate 40 line (say Oklahoma City OK to Knoxville TN), and the freeze line could push well into Mexico at some point during the medium range.

"Piedmont" Or "Miller A Hatteras Low" On January 17 - 20?

The latest runs of the various numerical models agree on the threat for a major winter storm in the medium range. Most of these outlooks show the greatest threat for important precipitation to be over the eastern third of the U.S. But there is some disagreement on the potential track of the cyclone, for the reasons that a) it is still far away in time and b) the placement of the cAk boundary may be either inland or off the coast. The differences in scenarios for the trajectory and structure of this low boils down to a Piedmont type of storm, which would be primarily rain for the Interstate 95 corridor but an ice and snow monster for Appalachia and the lower Great Lakes, or possibly another Nor'easter, similar in path but probably far stronger than the low predicted to affect the major cities of the Mid-Atlantic and New England states in about three to four days. At this time, I lean toward the operational model depiction of the disturbance tracking slightly to the left of the Atlantic shoreline.


EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)


Another Vicious Arctic Cold Shot For Your Troubles!

I doubt very much that the intrusion of Arctic air experienced during the medium range will be a "one and done" deal. If you look at forecasts of the position of the cAk vortex, the feature actually deepens and sags into N QC (the Ungava Peninsula) through the extended period. Motherlodes in this position teleconnect well with much below normal temperatures to the east of the Rocky Mountains, with a concentration of the coldest readings over the Midwest, Northeast, and of course eastern Canada. Most of the ensemble members of the GFS and ECMWF versions show a second, serious stab of brutally cold air sweeping from Alberta and Saskatchewan through the Great Plains into the Deep South and Eastern Seaboard. In keeping with the previous Arctic blast, the surface cold front penetrates deep into Central America.

To make matters worse, the various equations seem to hold on to the Alaskan block and Ungava gyre through 384 hours, which suggests that even with a warm-up after the extended period, yet another sharp drop in temperatures could occur in at least the northern tier of the U.S.

Ungava Vortex, Alaskan Omega Block Favor A "Miller B" Type Nor'easter

There is also the specter of the Kona Low near Hawaii which, as the polar westerlies breach the lower portion of ridging along the West Coast, could reach Oregon and California late in the extended period. The disturbance could interact with the trough complex linked to the giant cold dome in Quebec. If that is the case, redevelopment may occur in the favorable Cape Hatteras position. Consider that the current forecast is for two major coastal storms over the next 15 days. The synoptic setting would easily favor a third such disturbance around January 24 or thereabouts.

Prepared by Meteorologist LARRY COSGROVE on
Thursday, January 10, 2008 at 6:50 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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