WEATHERAmerica Newsletter, Tuesday, New Year's Day, January 1, 2008

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)
AB....SK....MB....ND....SD....N NE....WY


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

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

Isolated Locations In
NL: SE NWF
(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
N, W MI....N IN....N OH....NW PA....W NY....ON Peninsula
(Snow; in Squalls; 4 - 12")

Isolated Locations In
BC....W WA....OR Coastal Ranges
(Snow; Above 3000 Feet; 4 - 12")

Scattered Locations In
NB....PEI....extreme E QC....NL: W NWF
(Snow; 4 - 12"; Near-Blizzard)

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)

Freeze Likely Across the Deep South Next Two Nights....

To be sure, there have been worse cold intrusions into the Gulf Coast and FL. But the recipe for a quick drop in temperature across the Deep South is for very low dewpoints and slackening winds, and that formula will be in effect for the next two or three nights. And the regime moving into the Cotton and Citrus Belts is truly Arctic; note that the 850MB 0 C isotherm actually touches the shoreline of the Gulf of Mexico, and the surface freeze line dips well south into Mexico as well as the Florida Peninsula. This arid air mass will warm quickly in daytime, but the nocturnal drops in these normally warm areas may take as much as four days to eliminate due to the dryness of the atmosphere.

....Followed By Quick, Massive Warming Across Eastern Two-Thirds Of U.S.

Talk of cold air aside, the trough carrying this frozen domain is progressive and should be exiting through new England within 72 hours. With a deepening trough present over the western states, a growing area of very warm (and initially dry) values from Mexico will advance into the Great Plains by Friday, then build through the Atlantic Coastal Plain during the weekend. Since moisture from the Gulf of Mexico will be added to the atmosphere, forecasts for thermal anomalies are probably too warm for the Upper Midwest and Great Lakes, what with existing snowpack and expected cloud cover with rainfall. That said, the outlook is still quite balmy for southern Canada and the U.S. to the right of the Rocky Mountains for the next four or five days. It is entirely possible that the 70 deg F isotherm will reach the Interstate 80 corridor (Omaha NE to Tenafly NJ) at some point during the next 144 hours.

Storm Sequence Over The Pacific Ocean Edges Closer To The West Coast

Deep tropical connections from the equatorial Pacific Ocean are not the "norm" for a well-developed La Nina episode. Yet when you review satellite data from MTSAT and GOES West, the linkage to abundant tropical moisture is active in three places: Malaysia, just west of the Hawaiian Islands, Near Baja CA, and across Central America. The particularly impressive fetch is that "Pineapple Connection" nearing HI, and the bad news is that in the next 72 - 120 hours will take dead aim at Oregon and California. Rain will reach the Golden State on Friday, with the threat of floods, mudslides, and high elevation blizzards or avalanches in place this weekend. See more on this topic below.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

Split Decision: Warm, Docile In The Eastern Half Of The U.S., Cold And Stormy Across The West

Until events upstream force a breakdown in the 500MB longwave pattern, you could best characterize the medium range pattern as a decidedly Cold West, Warm East configuration. Even with added high dewpoints from the Gulf of Mexico moisture source, readings will still be 15 to 20 deg (F) above seasonal averages Between January 5 and 10 in locations to the right of the High Plains.

Possible High Plains Blizzard January 5 - 8 (With Severe Weather In The Warm Sector)

There is excellent model agreement on an extreme storm arising from the heavy rain event slated to target CA and OR around the 96 - 144 hour time frame. Just when the low will emerge east of the Front Range is uncertain, but around Day 5 through 7 seems most probable. The storm track will almost certainly be a leftward variant of the Panhandle Hook "A" type, which implies a high wind and heavy snow event from N NM into the western and central portions of the Dakotas. The extreme depth and often closed signature of the 500MB low (with an associated full-latitude trough) tells us that severe thunderstorms are also destined to be an issue for localities in KS, OK, and TX early next week.

Southeast Ridge Returns With a Vengeance (For Now)

A heat ridge is almost certain to be the byproduct of the massive storm complex over the western states, with the net result of producing some almost summer-like warmth to the Eastern Seaboard from FL to NJ (really...) by early next week. This anticyclone will be transient, which means that as the trough across the Intermountain Region progresses eastward and a cA vortex builds in the Prairie Provinces, 500MB heights and surface readings will inexorably fall after January 11.


EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

Strong -EPO Signal = Major Change In The 500MB Longwave Pattern

I am convinced that the period between January 12 and 22 is going to feature some pretty brutal weather across the entire lower 48 states. The reason for such a bold (and perhaps frightening) statement is because of the agreement among the various computer models about the change in the 500MB longwave pattern. Instead of all of the Arctic air being bottled up in Siberia, the coldest values shift to Canada in the extended period. The lingering cA vortex over the Kamchatka Peninsula acts in concert with the new motherlode to build an extensive -EPO/-AO ridge complex that forces colder values southward into the lower 48 states. A flat subtropical high, meanwhile, positioned across Cuba and the Bahamas will act as a moisture pump and help to maintain a sharp baroclinic zone from S TX into the Gulf Stream. With a vigorous storm track along this banding, we may see extensive cold and frozen precipitation from the lower Great Plains into the Mid-Atlantic region.

And yes, everyone from the Intermountain Region into the Northeast is going to be very, very cold....

How Is "La Nina" Doing?

The ongoing -ENSO episode is undergoing some critical changes that should lead to overall weakening in about 45 to 60 days. While the SST anomaly is still very impressive in its western and central sectors, note that the eastern portion of the equatorial Pacific Basin is warming slightly. Most likely the ebb and flow of the La Nina will continue through this month, as signals such as the SOI are still very bullish on the thermal disparity remaining. But the warmth trying to take shape over the Galapagos islands will migrate westward, resulting in a gradual return to a neutral oceanic character by April 1. What this prospective change means to weather trends is this: drought will probably cease this spring over locations east of the Rocky Mountains. And the coming spring in the northern tier may not suffer from dreary and cold conditions associated with "The Little Girl".

Prepared by Meteorologist LARRY COSGROVE on
Tuesday, New Year's Day, January 1, 2008 at 4:05 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 2007 by Larry Cosgrove

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