WEATHERAmerica Newsletter, Saturday, January 17, 2009, 5:35 PM CT

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TODAY'S FUN LINKS: OLR Depiction The Gateway to Astronaut Photography of Earth

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
(Orographically Derived)
BC....ID....W MT....W WY....W CO....NW NM....NE AZ....S UT....NV....OR....WA


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

Isolated Locations In
Coastal LA, MS, AL....N FL....S GA....E SC....Coastal NC
(QPF 1 - 2")


WINTER WEATHER OUTLOOK
(potential for minimum temperature to drop below 10 deg F, or for excessive/dangerous frozen precipitation events within the next 24 hours)

Isolated Locations In
SW MN....IA....C, E MO....C, S IL....S IN....KY....E TN....W NC....W VA....WV....PA
NY....C, E ON....MI
(Snow; In Squalls; 2 - 8")

Scattered Locations In
CT....RI....MA....VT....NH....ME....NS....NB....S QB
(Snow; 4 - 12")

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)

Finally, An Eastern Seaboard Snow Event (Well, Sort Of....)

There IS a disturbance over the Great Lakes which presents a snow threat to the Interstate 95 corridor on Sunday night and Monday. That said, the poor organization of the surface structure with the upper level low is likely to prevent a truly critical snowfall event outside of New England. The parent feature, embedded in the vast 500MB trough, may generate heavier snow squalls throughout parts of the Corn Belt and Appalachia. The wave along the surface front, which should organize near Raleigh NC on Sunday, will remain separate from the low aloft until both disturbances merge below Nantucket MA early January 19. After that time, moderate to heavy snows will probably affect a swath from Providence RI into New Brunswick and Nova Scotia, with up to a foot of snowfall possible.

Colder Air Stays Put Over The Eastern States....

It may be true that the cold air sitting over the eastern half of the nation is not in the same league as the brutal air mass that recently passed over the Midwest and interior Northeast. That said, temperatures will still run far below seasonal normals from the Mississippi Valley to the Atlantic Coastal Plain. The +PNA configuration (with the powerful ridge complex over British Columbia) has a ways to go before it breaks down.

....While The West Coast And Great Plains Warm Up

Outside of the valleys of the Intermountain Region (with a strong inversion in place), the impressive +PNA ridge complex is allowing for a run of above normal temperatures. This is especially true along the Pacific shoreline and middle/lower Great Plains, which could have record warmth in spots over the next few days. Downslope mechanisms in California and the High Plains may allow for daily maxima to exceed 80 and 70 deg F, respectively.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

Colder North, Milder South Alignment?

One theme present among the numerical versions covering the medium range is that the +PNA configuration will break down, giving way to a low-slung zonal flow across the lower 48 states. In this set-up, a cAk vortex elongates and deepens across northern Canada. Disturbances in the southern branch of the jet stream may either phase with the polar and Arctic branches (as seen with a possible Colorado/Trinidad cyclone January 23 - 28) or remain independent and create a moderate rain or ice episode across the southern tier of the U.S. (the ECMWF outlook sees such a possibility January 24 - 25). Of concern is the rather impressive cold low west of Baja California, which was initialized by the European scheme but not by the operational GFS equation. If enough cold air becomes entrained into this feature, a serious icing event may unfold in the Red River and Tennessee Valleys.

Despite the lack of any blocking signatures, the vast motherlode encompasses the northern half of the nation and all of Canada. Such a configuration can happen during La Nina episodes, with the generally flat flow punctuated by storms that move roughly along 40 N Latitude. So whereas the Gulf Coast sees only passing cases of cold advection, cities such as Chicago IL and New York NY can experience some numbingly chill readings.

Major "Colorado-Trinidad A" Storm Possible On January 25 - 27

On the idea that the disturbance west of Baja California should be treated as an independent entity (creating a moderate rain and perhaps icing event across Dixie around January 23 - 25), the next truly major winter storm looks to evolve over southern Colorado during the medium range. Energy from the trough complex over the central Pacific Ocean is predicted by most of the computer models to break away and move beneath the huge +PNA ridge. Emerging along the NM/CO border on or about January 24, the low is likely to take a path toward the lower Great Lakes by January 26. Therein lies a complication.

With so much cold air across Canada and the northern U.S., a redevelopment scenario seems probable. The GFS scheme supports a new center over S VA, with the new center deepening rapidly and passing through or just below a PHL....NYC....BOS arc. This is the sort of track (keeping in mind the nearby cAk regime) that can generate a healthy area of sleet and freezing rain. The worst hit may well be the Shenandoah and Susquehanna Valleys. But should the secondary cyclone pass below Long Island NY, the lower Hudson Valley and populous southern New England could get an ugly replay of the famed New Year's Day storm of 1973. The middle Front Range, Great Lakes and QB Eastern Townships, at this early juncture, would be most favored to see important snow accumulations.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

Madden-Julian Oscillation: Still Alive And Kicking

The MTSAT image shows an unmistakable teleconnection associated with tropical forcing. A deepening vortex below the Kamchatka Peninsula has a broad linkage with a plume of moisture and energy over the southwestern Pacific Ocean. With the gyre pushing into the area just southwest of the Aleutian Islands, it seems likely that a another round of amplification will begin over the Arctic Ocean. Most of the computer outlooks take this new motherlode into Alaska and the Yukon Territory, with further expansion southeastward toward the Upper Midwest and Great Lakes. If not for the MJO association, the polar westerlies might well be relatively flat and temperatures in most of the U.S. mild.

Alaskan Vortex Vs. A -NAO Signal: Round 2!

December saw a reversal of a +PNA configuration to a pattern dominated by a vast cAk dome over Alaska and the Yukon Territory. While the current +PNA jet stream alignment looks quite sturdy, there is nearly unanimous agreement among the ensemble packages that the Arctic motherlode will shift into the northwest quarter of the continent after January 28. You may recall that there was abundant cold air last month, with all but the Deep South and Atlantic Coastal Plain seeing repeated cases of bitter weather. This time around, I suspect that the Northeast will be involved in the cAk domain, mostly because the various models are showing breakaway pieces of tundra values following an active storm track from the lower Front Range into the Delmarva Peninsula. But the worst of the frigid regime will fall into place across the Pacific Northwest into the Great Lakes region, with plenty of snow and ice accompanying the drop in temperature.

A Sneak Peak At February

With the Arctic motherlode likely to become ensconced over Alaska and northern Canada as we enter February, a pattern very much like a "typical La Nina" episode could be taking shape. I reviewed past winters where a -ENSO measure was in decline through January, and found that the 500MB analogue summary for the first day of February bore a striking similarity to the GFS and ECMWF ensemble forecasts for 02/01/2009.

Most La Nina winters ultimately see a strong ridge formation develop near Cuba and the Bahamas, with gradual building and advancement into Florida and Georgia by the arrival of calendar Spring. For this reason, I can see excellent potential for bouts of overrunning precipitation, with a likely surplus of moisture over the Southeast and lower Appalachia (but not including FL). With cold air holding tough over the Midwest and Northeast, a recipe for major ice storms is present from the central Mississippi Valley into the central and northern Mid-Atlantic region. Conversely, readings may occasionally trend very mild or warm across the southern tier of the U.S., as storm after storm takes the favored Colorado/Trinidad and Panhandle Hooker tracks.

Prepared by Meteorologist LARRY COSGROVE on
Saturday, January 17, 2009 at 5:35 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 2009 by Larry Cosgrove

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