WEATHERAmerica Newsletter, Tuesday, February 19, 2008 at 8:20 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)
STRONG WINDS
(Pressure Gradient Derived)
OK....W KS....E CO....W NE....W SD....NE WY....E MT....W ND

Some Thunderstorms May APPROACH Severe Limits
Coastal TX, LA


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

Scattered Locations In
E TX....C, S LA
(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)

Isolated Locations In
OR....N, C CA....NV....N AZ....UT....W, C CO....NW NM
(Snow; Above 3500 Feet; 4 - 12")

Isolated Locations In
SE IN....OH....E KY....WV....W MD....S PA
(Snow; 3 - 6")

Isolated Locations In
E QC....NL/LBR
(Snow; 4 - 8")

Isolated Locations In
W ND....W SD
(Snow; 3 - 6")

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)

The Midwest And Northeast Look To Stay Cold....

Yet another intrusion of Arctic air is following on the heels of the major storm that raked the eastern half of the nation this past weekend. A shortwave will precede the next blast of colder values, producing as much as 6 inches of snow in elevated areas of KY, WV, W MD, and S PA (with squalls elsewhere in the Ohio Valley totaling as much as 2 - 4 inches). This reinforcing shot of cold air will probably be progressive, lasting only into Thursday before moderating. Still, the 0 deg F isotherm on Wednesday night and Thursday morning may reach as far south as an Interstate 80 arc from Joliet IL to Columbia NJ.

....While The Lower Great Plains And Gulf Coast Retain Some Warmth

At the same time much of the northern half of the U.S. is involved with Arctic air, the southern tier (especially close to the Gulf of Mexico) will remain relatively mild. A frontal structure is forecast to set up close to an Interstate 20 line (Fort Worth TX to Columbia SC), with repeated shortwave motion along the boundary preventing cA values from moving southward. Each of these impulses will have an increasingly moist, and unstable, regime to work with in producing showers and thunderstorms. Some potential exists for severe weather and heavy rainfall along the Gulf Coast during much of the near term.

Pacific Ocean Storm Sequence Looms On The Horizon

The latest round of disturbances generated over the northern Pacific Ocean will be arriving along the West Coast on Thursday and Friday. Digging under the positive height anomaly covering Alaska and western Canada, the lead impulse will trigger heavy rain and snow in much of the West. Another consequence of the storm sequence will be lowering temperatures and creating instability over California and the lower Colorado River Valley. Lowering snow elevations, hail and strong thunderstorms are probable in the 48 - 72 hour time frame in much of the Southwest.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

Santa Ana Is Coming To Town

Once the second and strongest impulse in the Pacific Ocean storm sequence passes through California (about six or seven days from today), surface pressures will rise dramatically across the Great Basin and Salt Lake Valley. The sudden arrival of ridging to the north of the Golden State will create a fast, downslope flow, rapidly heating and drying the incoming mP regime. While probably not a long-lived event, potential exists from damage from gusts and rapid drying along the Interstate 5 corridor at the start of the medium range.

Last Week Of February Is Storm Time

The 18z GFS model run only clarified what was seen in the 12z depictions of the American and European schemes. Namely, that the prospect exists for a fairly massive winter storm affecting the eastern two-thirds of the nation within a week. Some caution is needed in making a forecast for this feature, as an Arctic-based shortwave is predicted to link with the disturbance around February 26 and 27. This could result in a further west track of the surface low; for now the equations seem to lean toward a center-jump or redevelopment scenario that takes the greatest pressure falls along a Roanoke VA to Boston MA line. Try as we might, none of the computer outlooks support a major fall of snow along the Interstate 95 corridor. But the depth and power of the cyclone is, from this vantage point, impressive, and other twists and turns may emerge that could lead to a more wintry landscape in the snow-starved streets of weather enthusiasts in the highly populated areas of the Mid-Atlantic and southern New England regions.

Regardless of how the snow and ice pattern develops, the odds are very favorable for another "blaster" system that generates its fair share of heavy rain and severe thunderstorms in its warm sector and near-blizzard conditions in parts of the Midwest, Great Lakes and interior Northeast.

+PNA Pattern Gone Wild?

While not a cross-polar flow mechanism in the truest sense, the highly arched 500MB ridge that sets up during the 6 - 10 day time frame is still extremely impressive. Deriving air from an eastern Siberia source region (yes, it is plenty cold in the Chukchi Peninsula...look it up!), the jet stream configuration is like a +PNA configuration on steroids. Possible side effects: acting to "juice" the Midwest and Eastern Seaboard storm during the medium range, as well as sending a brief shock cold wave into northern Mexico and the Deep South.


EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

The Equatorial Energy Connection

I am fairly confident that more wintry twists and turns await North America during the first week of March. While the extraordinary subtropical jet stream appears to be fading over the equatorial Pacific Ocean, another lower latitude phenomena has reappeared time and again across the Orient. This "tropical connection" is normally found in strong phases of the Madden Julian Oscillation. What continues to happen is a pronounced flow of moisture and energy from Indonesia and Oceania into the polar westerlies (which are depressed by an equally bizarre presence of bitter cold air across eastern Asia). This boost from the lower latitudes strengthens storms emerging over the Japan Trench which, upon progression south of the Aleutian Islands, build high-amplitude ridge complexes in either the EPO or PNA positions. In this manner, Arctic air builds in western Canada and drains into the U.S., while at the same time the storm sequence undercuts the positive height anomaly and brings turbulent weather to the lower 48 states. Since the pattern appears to be locked in (see the broad plume of cloudiness in the Far East...), I suspect that March will finally deliver some of the lower than normal temperatures and frozen precipitation that some U.S. residents east of the Rocky Mountains have been waiting for.

But in this crazy year, it would be unwise to provide specifics....

Prepared by Meteorologist LARRY COSGROVE on
Tuesday, February 19, 2008 at 8:20 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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