WEATHERAmerica Newsletter, Saturday, November 8, 2008 at 3:55 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)
STRONG WINDS (Pressure Gradient Derived)
W ON....N QB

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

Isolated Locations In
Coastal WA, OR
(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
W ON....Upper MI....N WI
(Snow, In Squalls; 2 - 6")

Isolated Locations In
W AB....BC....WA....OR....N CA....N NV....N UT....W WY....W MT....ID
(Snow; Above 3500 Feet)

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)

Hurricane Paloma Targets Cuba, Then The Bahamas

Category 4 Hurricane Paloma will make landfall over eastern Cuba late Saturday night, likely creating great damage to agriculture before reaching the Bahamas as a tropical storm or depression on Monday. Besides the economic impacts, the hurricane may, as the center shears apart, contribute energy to the polar westerlies. That merger of storm remnants with the jet stream will aid in creation of a mean 500MB trough over the eastern half of the U.S., enabling a colder temperature profile and a rightward deflection to disturbances approaching from the northern Pacific Ocean.

Surge Of Colder Air Across The Midwest, East....

The storm and upper low which brought massive snows and strong winds to the Dakotas is now moving through the Great Lakes toward Quebec. With ridging across western Canada, a mechanism is in place for cold advection which, in time, will reach the urban Northeast. Enough energy is accompanying the cold transport so that snow showers and squalls are probable over the following 72 hours in the usually suspect downwind areas from Lake Superior, Michigan, and Huron. By Monday night and Tuesday, the threat for important snowfall from lake-effect or lake-related causes will have spread into N OH, NW PA, and W NY.

....While Weak Storm Forms Over Texas Early Next Week

This is the time of year when frontal waves and resultant cyclogenesis starts to occur at lower latitudes. One such low pressure center will form in N TX on Monday night, triggering showers and thunderstorms along its frontal structure and stratiform rain over parts of OK and the TX Panhandle. This feature will likely run into confluence over Appalachia and the Northeast, not strengthening but spreading mostly nuisance precipitation across the eastern third of the U.S. during the early portion of the new week.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

Powerful Storm Builds Mean Trough, Pulls Down Colder Air From Canada....

In a sequence of three storms, the middle impulse often tends to be the strongest. There is general agreement among the numerical models that the vigorous disturbance south of the Aleutian Islands will initiate an intense surface low over TX in five to six days. The track of this storm will almost certainly be similar to the one preceding, just west of the Appalachian Mountains into E QB and ME. That path will allow for some warming along the Eastern Seaboard, meaning a rain event and not snow. Severe thunderstorms are possible over parts of the Dixie states, which a mix or change scenario of rain to snow seems a good bet for much of the lower Great Lakes. It should be stressed that the most important aspect of this cyclone will be its capacity to establish a mean 500MB trough and cold air advection through the eastern half of the U.S. by November 17.

....While Warm Ridge Complex Builds Across The West

A modest +PNA signature will develop through the medium range. In conjunction with an equally moderate alignment of -AP and -NAO signatures, the ridging over the western U.S. will aid in maintaining a cold trough complex across the eastern two-thirds of the nation. At the same time, the stable, generally warm nature of the ridging should keep much of the West, especially California, under above normal temperatures between November 11 and 18.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

Will The Warmest Air Stay Across The Intermountain Region, Great Plains?

Review of the numerical models and the respective ensembles shows a possible issue with temperature forecasts during the extended period. While the broad (and unseasonably cold) trough complex over the eastern half of the nation clearly dominates the first portion of the 11 - 15 day range, there are some questions as to whether the relatively mild air over the Intermountain Region will push eastward. The operational GFS and its variants show a -PNA arrangement with cold air through the West and impressive moderation from the Great Plains to the East Coast. But the Canadian and European model suites are decidedly cold in the Midwest and Atlantic Coastal Plain through November 23. At this point in time, I think the American scheme has the right idea, with a warming trend to the right of the Front Range between November 22 and 28. But previous to that time, look for significant lake-effect snow events and areas of much below normal temperatures over an area from the High Plains into the Deep South and Eastern Seaboard.

Equatorial Impulses May Play A Role In Colder Trends For 11 - 15 Day Range As Well As Early December

The measure of activity with the Madden Julian Oscillation is nowhere near being an exact science. That said, the presence of two impulses (one moderate over the Indian Ocean, the other quite strong across eastern Africa) imply two sequences of amplification to the North America 500MB longwave pattern, when and if these waves reach the western Pacific Ocean. Already there is some connection with shortwaves in the polar westerlies, which may be taken as a sign that the slow-to-warm (over the eastern U.S.) ECMWF and GGEM model solutions are correct in the 11 - 15 day time frame.

Prepared by Meteorologist LARRY COSGROVE on
Saturday, November 8, 2008 at 3:55 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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