WEATHERAmerica Newsletter, Sunday, December 23, 2007 at 8:45 P.M. ET
SEVERE WEATHER OUTLOOK
(potential for tornadoes, damaging winds, and large hail within the next 24 hours)
Some Thunderstorms May APPROACH Severe Limits
HEAVY RAINFALL OUTLOOK
(potential for an inch or more total rainfall within the next 24 hours)
Isolated Locations In
Coastal BC, WA, OR, N CA
(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)
Scattered Locations In
BC....WA....OR....N CA....N NV....N UT....W WY....ID....W MT
(Snow; Above 3500 Feet; 4 - 12")
Scattered Locations In
(Snow; 4 - 8")
Scattered Locations In
(Snow; 4 - 24"; Near-Blizzard)
Scattered Locations In
S ON....MI....N IN....N OH....NW PA....W NY....S QC
(Snow; In Squalls; 4 - 16")
SHORT RANGE OUTLOOK
(Through The Next 72 Hours)
Another Quick Appearance By Arctic Air
That is ARCTIC air noted across the Prairie Provinces and Midwest, a gift from the major winter storm now departing North America through E QC. And while the shot of cA values is transient, it is part of a pattern of rapid intrusions of rather cold air that follow storms from the Great Plains into the Northeast. The current colder regime will modify Monday and Tuesday, but will likely be succeeded by another tundra domain in the medium range.
Lake Effect Snow Machine Is Alive And Well
The combination of a strong upper low and cold pool with relatively warm, open waters of the Great Lakes means a likely White Christmas for the likes of Cleveland OH and Buffalo NY. The peak of the squall event will not be until Christmas Eve night, when the core of 500MB vorticity and cA values passes into upper Appalachia. Some communities downwind of the major water bodies may see as much as three feet of new snow by Christmas morning.
In The Southwest, It Will Be "Mild With Showers And Thunderstorms"
Mild if you live along the coastline of CA and in the deserts adjacent to the Colorado River. But higher elevations in the Southwest will feel a chill, and thunderstorms dotting the region could be rather strong due to a steep lapse rate and orographic effects. The trend toward the medium range will be for colder air and stronger winds to lock in over the Desert Regions.
MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
The Pacific Northwest Loves La Nina
I am joking, of course! The current deep storm is but one symptom of how the La Nina episode is affecting the weather patterns of the U.S., with the Pacific Northwest getting set up for more huge storms and high wind events. The next arrival is slated for Christmas Night, with the snow line getting down to 2000 feet and rainfall totals in some of the coastal communities exceeding four inches. Wind will be treacherous, with Interstates 84 and 90 impassable in a few stretches. The worst impacts, however, are slated for December 30 - 31, when a particularly intense cyclone digs southeastward through the Gulf of Alaska.
Active Storm Track Continues, With A Few New Wrinkles
This is going to get ugly.
If you view the weather record back to the first week of November, you will find a pattern favoring an active storm track from eastern Asia through the central and northern U.S. As winter approached the disturbances became deeper with greater drainage of cold air (hey....where is all that warming that was supposed to be over the Great Plains and Canada, huh?), with temperatures rising sharply after 48 hours from passage through the Old South and parts of the Eastern Seaboard.
Things have not changed, and I suspect that the same general scenario for storminess will continue through the first two days of the New Year, before a fairly dramatic change occurs in the 500MB longwave pattern (see below). One cyclone, possibly of the Chattanooga Choo - Choo type, will organize as a strong shortwave cuts through the Mid-South around Day 7. This feature could provide a shock snow and ice event along the Interstate 95 corridor close to New Year's Eve. But the real monster in our midst is clearly visible over the Aleutian Islands. While path predictions are a bit up for grabs (the most likely outcome: something approximating a Galveston Bay Spin-Up, from TX into middle Appalachia), drainage of cold air and widespread heavy precipitation seem likely. This feature could be a prolific severe thunderstorm producer, and at the same time set up a thick stripe of heavy snow and ice affecting much of the Corn Belt and interior Northeast in the January 2 - 3 time frame.
How About That Bahamas Heat Ridge?
Like the famed "Energizer Bunny", the persistent subtropical high centered over the Bahamas will maintain a presence through Day 10. The ridge serves two purposes: one to keep the Gulf Coast and Southeast (and occasionally, the Mid-Atlantic region) out of harm's way when cold shots drop out of Canada. But as long as the positive height anomaly remains, each storm advancing across the country (and there have been many) is assured of a healthy dose of tropical moisture from the Gulf of Mexico. So with perhaps three major disturbances coming up in the sequence stretching back to Japan (and one whopper of cyclone near the Aleutian islands scheduled to impact the lower 48 states late in the medium range), we can expect more heavy precipitation events to track through the nation. If you live above 40 N Latitude, some of that precipitation is going to fall as snow and ice between now and January 3.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
Words like "tumultuous" and "crazed' come to mind in describing the possibilities for the longer term forecast. With deepening longwave signatures across the Northern Hemisphere, a convective outburst associated with a Kelvin wave over Indonesia and Oceania, and an extensive (and, likely, getting thicker and broader) snow pack over Canada and the northern half of the U.S., the probability for a highly volatile trend in weather seems likely during the first week or so of 2008.
We can start the discussion of the extended outlook with the major storm coming out of TX on Day 10. The most likely path for this feature will be into C PA, then into NS, during the 264-288 hour time frame. But depictions of the 500MB height anomaly chart show some potential for redevelopment over the VA Capes on January 3, in which case a change to snow would occur along the Interstate 95 corridor from Washington DC to Boston MA (followed by the obligatory two-day shot of cold air). I should emphasize that while I think this particular low will be a "cruncher" with major travel and energy disruptions across the eastern two-thirds of the U.S., it will NOT be the ultimate "pattern changer". That description most likely will fall to a storm now exiting the coastline of Japan.
First up is the huge storm forecast to move from TX to middle Appalachia. Although the 18z Dec 23 GFS data seemed to lose this system (along with every other storm), the preponderance of model runs suggests that after carving out a full-latitude, neutral-tilt 500MB trough through the Intermountain Region, cyclogenesis near Sherman TX will give rise to an impressive disturbance that will spread severe weather across much of the Old South while plastering the Midwest and much of the Northeast with heavy snow and ice (as well as strong winds). The cold air drainage attendant with this feature may reach as far south as central Mexico and western Cuba at some point in the extended period (January 3 - 7 2008).
Prepared by Meteorologist LARRY COSGROVE on
Sunday, December 23, 2007 at 8:45 P.M. ET
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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