WEATHERAmerica Newsletter, Saturday Evening, February 23, 2008 at 6:00 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)
ISOLATED Severe Thunderstorms
(Microbursts, Large Hail, Isolated Tornadoes)
CA....S NV....W AZ


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

NUMEROUS Locations In
CA
(QPF 1 - 5")


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
S IN....N, C KY....S WV....W VA....W NC....E TN
(Snow; 3 - 6")

Isolated Locations In
N GA....N SC
(Sleet, Freezing Rain; Some Glazing Of Highways)

Scattered Locations In
CA....OR....WA....ID....W MT....W WY....W CO....NW NM....N AZ....UT....NV
(Snow; Above 4500 Feet; 4 - 36")

Scattered Locations In
QC....ON
(Snow; In Squalls; 4 - 8")

Isolated Locations In
W AB
(Snow; 4 - 8")

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)


Huge Storm Moving Into California....

You do not need the almost textbook" satellite view posted to get the idea that the storm moving into the Golden State is something special. UVV and moisture forecasts on computer models are impressive, too, and some of the predictions for wind exceed 60 m.p.h. in both pressure-gradient related gusts and with thunderstorms, which may become severe in much of the Southwest on Sunday afternoon and evening. The low serves a good purpose in reducing ongoing drought concerns through the Great Basin, but will also renew fears of mudslides and avalanches across much of California into the Lake Meade drainage area of Nevada and Arizona. Snowfall may reach as much as three feet in the High Sierra Range, with similar amounts of skier's gold possible for resorts in Utah and Colorado over the following two days.

....Will Have Nationwide Repercussions


Computer forecasts have been very bullish with regard to the intensity and character of weather associated with the California storm. Upon exit into the Front Range of Colorado on Monday morning, the disturbance will slowly begin to channel moisture off of the Gulf of Mexico. Heavy snow, with a thin stripe of ice, is expected to break out and spread across the central and lower Missouri Valley. Strong thunderstorms may fire in a bubble of unstable air in parts of central and eastern Texas, then slowly link to precipitation bands forming within the warm and overrunning sector. As the various numerical models have tended to shift toward the scenario of the respective ensemble members (a fairly classic Colorado/Trinidad "A" path), snowfall and glazing threats have increased accordingly for the Milwaukee WI, Chicago IL, Detroit MI, and Buffalo NY metropolitan areas (se above map). Strong winds could also create near-blizzard conditions in areas under the highest snowfall rates. There is some potential for the heaviest snow banding to shift into coastal New England IF the 12z GGEM panels verify, but for now the best snowfall risk will be in locations downwind of the major lakes that have orographic enhancements at work.

Time For Another Intrusion Of Arctic Air

When the major winter storm emerges into the Great Plains by early next week, its circulation will phase with an oncoming shortwave from the Prairie Provinces, creating a full-latitude trough. As ridging will exist in the +PNA position (roughly from AK into CA), cold air drainage will be facilitated. The inbound Arctic regime will be most pronounced over the Midwest and Northeast, where record low temperatures may occur on Days 4 and 5. Further south, however, the reduction in dew points with the new air mass will allow for nocturnal drops in readings, with frost possible along the Interstate 10 corridor on Tuesday and Wednesday nights of next week.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

More And Stronger Storms In The Offing....

Satellite images are often a useful tool, in that upstream disturbances can be viewed and assessed as future threats to North America. Alas, GOES and MTSAT depictions show ominous displays of cyclonic circulation and cold air stratocumulus below the Aleutian Islands and just east of the Japan Trench. The European and American forecast models are somewhat split on the two strongest storms, with the 12z Feb 23 ECMWF favoring the further west impulse as a danger to the U.S. around Days 9, 10, and 11. American NWP data, however, sees BOTH features as a risk to the nation and easternmost Canada during the medium range and extended period, accompanied by heavy precipitation, strong winds, and intrusions of Arctic air. When viewing the ensemble packages of the respective models, one comes to the conclusion that a "one-two punch" of weather extremes is likely between February 29 and March 10. The most likely track for the cyclones will be similar to that unfolding for the Midwest and Northeast, with perhaps increased risks of severe thunderstorms from the lower Great Plains into the Southeast (owing to a stronger flat subtropical high near Florida and the Bahamas ahead of the incoming low and upper trough).

....With Another Strong Dose Of Cold Air, Too!

If you had any ideas about an early start to Spring, guess again. While warmth will appear over the western states and the East Coast during Days 7 to 9, the action of developing strong storms against a recurrent +PNA ridge complex would seem to favor another "Arctic Blast". this one in place through the central third of the U.S. and Canada late in the medium range. On the flip side, downslope flow behind the incoming cold high pressure cell dropping into the High Plains may trigger a very warm, dry (and incendiary) Santa Ana wind event in California around March 3 or 4.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

An Ongoing Series Of Cold Intrusions And Storms?

(Click On Image To Go To JMA Satellite Imagery Site For Loop And Sector Capability)

The ongoing tropical energy and moisture feed into storms emerging off of the Eurasian continent continues with no sign of let-up. A function of the Madden-Julian Oscillation (disregard whatever those "diagrams" say about the MJO Phase....), this fetch conjoins with the polar westerlies largely because of the abundance of cold air and full-latitude trough complexes that occupy eastern Asia (easily shown on the very cold appearance of the infrared MTSAT view). So storms which otherwise would fall apart on the long journey across the Pacific Ocean instead are deepening, and in the process pumping up ridges in the EPO and PNA positions while aiming disturbed weather along the central portion of the West Coast. For this reason, the generally cold, stormy pattern that has been in effect across the U.S. (albeit with quick moderation just downstream of the storms) is likely to continue into the second week of March.

Prepared by Meteorologist LARRY COSGROVE on
Saturday Evening, February 23, 2008 at 6:00 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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