WEATHERAmerica Newsletter, Thursday, New Year's Day, 01/01/2009

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Weather Report Thursday January 1-Photo-11

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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)
WY....ID....MT....ND....SD


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

NUMEROUS Locations In
Coastal WA, OR, N CA
(QPF 1 - 4")


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)

Scattered Locations In
SW QB....C, E ON....MI....NE OH....NW PA....N, W NY
(Snow; 3 - 6")

Scattered Locations In
S BC....WA....OR....N CA....N NV....ID....N UT....W WY....MT....S AB....C, S SK....ND
(Snow; Mostly Above 5000 Feet; 4 - 36")

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)

Powerhouse Storm Hits The Pacific Northwest....

High winds and heavy precipitation have been a fact of life in the last two and half weeks over the Pacific Northwest. Spokane WA has sen its snowiest December on record, and may locations in the region have experienced new standards for ice, snowfall, and wind. While the thermal profile has warmed somewhat due to incipient ridge formation over California, abundant snows and damaging winds are once again pounding the northern parts of the Intermountain Region. With a cold domain backed up against the Rocky Mountains, blizzard conditions could set in across portions of MT and WY through Friday.

....And Channels Cold Air As It Heads For The Great Lakes

Apparently the Rex signature over Quebec will not suppress the disturbance headed out of the Pacific Northwest. The computer outlooks seem united around the scenario of the low center dropping into Kansas, then heading northeastward into the Great Lakes by Monday. The low will transform into an Arctic vortex, pulling down air from the Canadian tundra. Starting the first full work week of 2009, very cold air will cover most of the eastern two-thirds of the U.S.

Another Huge Cyclone Hits British Columbia, Washington on January 4, 5

There is another storm in the sequence over the Gulf of Alaska (easily visible on satellite imagery) which should race into BC and WA within the next 48 hours. The track of this feature will be a bit farther north (through Vancouver Island), which implies that the greatest precipitation totals will be in the vicinity of, and above, the Puget Sound and Olympic Peninsula. Still, this feature will increase the already deep snowpack across the Pacific Northwest as well as the northern Rocky Mountains.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

Triple-Tier Jet Stream Configuration, Massive Sub-Aleutian Storm = Big Problems In U.S. Next Week

GOES West imagery shows two streams of energy and moisture moving northeastward from the equatorial Pacific Ocean, with storm centers in the Kona and sub-Aleutian positions. This combination of synoptic features favors two teleconnections: increased western Canada ridging and important cyclogenesis in the lee of the Rocky Mountains. At this time, due to the positive 500MB height anomaly forecast over Greenland, it makes sense to follow the 12z ECMWF forecast of a Colorado/Trinidad type "B" storm that takes a more southern track along or just below the Ohio River and Mason-Dixon Line. Timing may be an issue here, as the GFS version suggests a faster path which exits the Mid-Atlantic coastline within eight days. But when considering the linkage with the subtropical jet stream, and incoming Arctic air mass, a possible cold air damming scenario (mostly north of the Potomac Valley), and the likelihood that the upper low may close off, the prospect of a major winter storm for the Midwest and Northeast emerges. This could involve not only heavy snow but also a band of glazing as well as strong thunderstorms within the warm sector.

Shift To +PNA Pattern At 500MB Favors Warm West, Cold East Alignment

The numerical models have been very aggressive with the building and intrusion of Arctic air, particularly in the second week of January. This trend continues, with all of the schemes centering the heart of the coldest values occupying the eastern two-thirds of the continent between January 8 and 15. With an open, but strong, 500MB ridge complex aligned along the West Coast, northwest flow aloft allows for air which starts out over the tundra of Alaska and the Yukon Territory to descend into the lower 48 states. There is a fair chance that an overrunning or wave cyclogenesis event could create a window for sleet and freezing rain across parts of the Deep South at some point during the medium range.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

Tropical Teleconnections From Pacific Ocean Argue For Warm West, Cold East....

As was the case last winter, the Madden-Julian Oscillation is having an effect on conditions in North America. Impulses generate over the Indian Ocean, move across Indonesia and the southwestern Pacific Ocean, and link with the polar westerlies. This linkage energizes the flow, allowing for waves in the jet stream to intensify to vortex status. In the process, warm advection aloft out ahead of these vortices (see one taking shape just southwest of the Aleutian Islands....) pumps up ridging along the West Coast. Those -EPO and +PNA ridges, in turn, set up a northwest flow and digging trough out across North America to the right of the Rocky Mountains. In plain English, all of the coldest air drains out of northern Canada into the U.S.

Another factor which favors a colder than normal winter season in much of the nation is the incipient La Nina episode in the equatorial Pacific Ocean. While my colleague Jan Null of Golden Gate Weather Services reminds us that the ENSO status, as viewed by measure of the ONI is still neutral (since it takes three consecutive months of a measure below -0.5 to be classified as a La Nina), the clear signature of the colder phase is evident on satellite measurements. With waters warming somewhat over the Gulf of Alaska, a weaker cold signal between the International Dateline and Galapagos Islands will almost always favor the colder +PNA, -NAO, and -AO configurations that have been seen during autumn and the beginning of winter.

....And Are Backed Up By Model Ensemble Forecasts

Going along with the idea of a strong winter storm affecting the East Coast later in the medium range, it seems likely that some especially bitter temperatures may take hold east of the Rocky Mountains through January 15. All of the ensemble means of the major forecast models show a very deep negative height anomaly across the eastern half of North America. So while California and much of the West sees warming and drying, lake effect snows and cold intrusions will be the rule from the Great Plains to the Atlantic Coastal Plain.

The 500MB longwave pattern may flatten out somewhat in mid-January, as the mean trough axis lifts out into the northern Atlantic Ocean (resulting in a +NAO signature). With a stronger subtropical jet stream and a more lateral flow aloft, an argument can be made that a January thaw will get underway over most of the lower 48 states. That may be, but one fly in the ointment to a warmer forecast is the presence of a deeply negative height anomaly below the Aleutian Islands, usually a precursor of stronger ridging in Alaska and British Columbia. That is a +PNA signature which, if it were to develop, would put most of the continent back in the proverbial icebox by January 22.

Prepared by Meteorologist LARRY COSGROVE on
Thursday, New Year's Day, January 1, 2009 at 6:05 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 2008 by Larry Cosgrove

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