WEATHERAmerica Newsletter, Sunday, February 10, 2008 at 7:20 P.M. CT

WEATHER HAZARDS (During The Next 24 Hours)

SEVERE WEATHER OUTLOOK
(potential for tornadoes, damaging winds, and large hail within the next 24 hours)
ISOLATED Severe Thunderstorms
(Microbursts, Large Hail, Isolated Tornadoes)
C, E TX

Some Thunderstorms May APPROACH Severe Limits
extreme N AR....C, E OK....SE KS....S MO....S IL....W KY

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

STRONG WINDS (Pressure Gradient Derived, Orographically Enhanced)
W CO....NW NM


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

Isolated Locations In
Coastal BC, WA
(QPF 1 - 2")

Scattered Locations In
C, E TX....C, E OK....SE KS....S MO....S IL....W KY
(QPF 1 - 3")


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

Isolated Locations In
E BC....N ID....MT....WY....N UT....NW CO
(Snow; 4 - 8")

Scattered Locations In
N NE....SD....S ND....S MN....N, C IA....N IL....SW WI
(Snow; 4 - 8")

Isolated Locations In
extreme S IA....N, C MO....C, S IL
(Sleet, Freezing Rain; 1/8" Glaze)

Isolated Locations In
C ON....W NY
(Snow, In Squalls; 4 - 12")

Isolated Locations In
QC....NL/LBR....PEI....NS....NB....ME
(Snow, In Squalls; Blizzard Conditions; 4 - 12")

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)


Marginal-Looking Storm Will Create Big Headaches In Midwest, St, Lawrence Valley

Its ragged appearance on satellite over the western quarter of North America may not look all that impressive.But the presence, yet again, of a deep tropical moisture connection and incoming cold air will mean more headaches for the eastern half of the U.S. over the following 72 hours. A stripe of overrunning precipitation may pose the greatest threat, with ice and snow from the Ozark Plateau into the Ohio and St. Lawrence Valleys by Tuesday. Enough upper level dynamics are present (and surface lifting mechanisms, too), for thunderstorms to fire across parts of the Old South. Some of these cells may be severe. However, instability and convective energy parameters are nowhere near as impressive as the February 4-5 system, so the risk of tornadoes and microbursts will likely be less over the worst-hit areas of AR, MS, AL and TN.

Brief Warming Trend For The Southwest, Lower Great Plains

There is substantial warming over California for much of the near term, and perhaps 36 hours of much-above-average readings for parts of TX and the Deep South on Monday into Tuesday. The overall look of the synoptic pattern, however, is cold, and the departure of the currently evolving storm in the Southwest should mean a return to colder temperatures for anyone living east of the Rocky Mountains and outside of Florida for the remainder of this week.

Next Up In The Pacific Northwest....

To use a line from an old, probably forgotten TV show (Second City TV, if you had to ask...), the GOES WEST image above could be termed "a thing of beauty, eh?" Note the entrapment of cold air in the northwestern quadrant of a Sub-Aleutian Low (cold air stratocumulus with its stippled appearance), and linkage to deep tropical moisture. This system will gravely impact the Pacific Northwest during the near term, with a harsh presence of strong winds and heavy precipitation that by 84 hours may encompass the Rocky Mountains of Colorado.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)


Get Set For Another Monster Storm....

The very same low pressure center which shows up so dramatically over the northern Pacific Ocean is depicted by most of the numerical models as having a significant impact on much of the continental U.S. between Tuesday and February 19. Complications with this feature are: a)presence of a strong subtropical jet stream within the warm sector; b) interaction with an Arctic shortwave; and c) conversion to a cAk motherlode over Quebec by late in the medium range. In addition to a substantial convective or severe weather threat, the disturbance may also create problems with winter precipitation and wind chills. The European version hints at redevelopment off of the Delmarva Peninsula on Day 7, which could enable a change (or maintenance of) to snow and ice in a "Miller B" scenario above the Potomac River.

....And Another Arctic Blast!

Return of bitter cold temperatures to the lower 48 states will be swift and unrelenting, with the possibility that the 850MB 0 C isotherm and surface freeze line could reach well into Mexico and Cuba for a time after February 17. The presence of so much Arctic air in the Laurentian Shield and Aroostook Valley would seem to favor a redevelopment scenario for the storm slated to affect the eastern states next weekend, raising the possibility that ice and/or snow could be a factor in forecasts for the Interstate 95 corridor on February 17 (note the surface high pressure center forecast by some models for that time over QC). Most importantly, however, is the threat for a prolonged cold spell along and east of the High Plains that could linger into the extended period.

Sub-Aleutian Low Equates To The Return Of Winter In Eastern Two-Thirds Of Continent

One of the sure signs of an impending Arctic intrusion in the eastern two-thirds of the U.S. is to look for a negative height anomaly between Hawaii and Unalaska. If the center of the 500MB trough complex drifts south of the Aleutian Islands, resultant 500MB warm advection will raise heights downstream in the EPO and/or PNA positions. If the core of the ridging reaches into the higher latitudes (above 45 N is a good reference point), then subsequent past-ridge digging will create a full-latitude trough and allow for intrusions of Arctic air masses. The critical point to make here is that the aforementioned major winter storm (see the signature over OH and 168 hours?) will serve as an accelerant to cAk drainage, allowing the lower temperatures to reach as far south as Cuba later in the medium range (while dislodging the heat ridge into the Sargasso Sea).

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

Split Flow Against Alaskan Ridge, Cuban Subtropical High Translates To....

While there is every likelihood of a national warming trend in the early stages of the extended period (vast vortex and trough complex lift out toward Greenland), teleconnections point toward another alignment in the jet stream configuration. The persistent subtropical jet stream links with a weakness over and west of the Hawaiian Islands, causing the 500MB flow to split with a trough forming between HI and AK. Ridging may then build over the eastern Pacific Ocean, with downstream digging of the northern branch into the U.S. The ensemble means of the GFS, ECMWF and GGEM show this effect in place by Days 15 and 16, implying: a) an active storm track through the southern and eastern states, and b) a tendency for below normal temperatures along and east of the Rocky Mountains.

Prepared by Meteorologist LARRY COSGROVE on
Sunday, February 10, 2008 at 7:20 P.M. CT

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 2008 by Larry Cosgrove

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