WEATHERAmerica Newsletter, Saturday, August 2, 2008 at 5:15 P.M. CT

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WEATHERAmerica Newsletter, Saturday, August 2, 2008 at 5:15 P.M. CT

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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)
SCATTERED Severe Thunderstorms
(Microbursts, Large Hail, Isolated Tornadoes)
MT....ND....MN....ON Boundary Waters....extreme S MB

Some Thunderstorms May APPROACH Severe Limits
LA....S MS....S AL....S GA

Some Thunderstorms May APPROACH Severe Limits
E AZ....NM....CO


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

Scattered Locations In
ME....NB....E QB
(QPF 1 - 2")

Scattered Locations In
MT....ND....MN....ON Boundary Waters....extreme S MB
(QPF 1 - 3")

Isolated Locations In
LA....S MS....S AL....S GA
(QPF 1 - 2")

Isolated Locations In
E AZ....NM....CO
(QPF 1 - 2")


EXCESSIVE HEAT OUTLOOK
(potential for maximum temperature to exceed 95 deg F within the next 24 hours)

Numerous Locations In
CA....SE OR....S ID....NV....AZ....NM....CO....UT....WY....S MT....S ND....SD....NE
KS....OK....TX....LA....AR....MO....IA....MN....WI....W, C IL....W KY....W TN....MS

Isolated Locations In
IN....C KY....C TN....AL....FL....GA....SC....C, E NC

TROPICAL WEATHER SUMMARY
(review of disturbances over the Atlantic Basin and Eastern Equatorial Pacific Ocean)

Eastern Equatorial Pacific Ocean


Atlantic Basin


African ITCZ


SHORT RANGE OUTLOOK
(Through The Next 72 Hours)



Yes, The Tropical Cyclone Threat In The Gulf Of Mexico Is Serious!

If you listed to Dr. Steve Lyons of The Weather Channel on Saturday morning, you got an excellent discussion of how a "home brew" disturbance from an old frontal structure can create a tropical cyclone over the Gulf of Mexico. The process that is now occurring south of Pensacola FL appears likely to yield a named storm, one which will push south, then west before undergoing a northwest to north recurvature around the back of the heat ridge centered over Missouri. The "worst case" analogue was mentioned by Dr. Lyons (Category 3 Celia, 1970) is important because the current system, at a higher latitude, could easily impact energy facilities below Louisiana and into coastal Texas early next week. Stay tuned!

Heat Ridge Expands Eastward From The Great Plains....

A 500MB heat ridge with a 595dcm core is not to be taken lightly, and the hotter air surrounding this ridge is already impacting much of the Intermountain Region, Great Plains and Deep South. A strong warm front, accompanied by heavy to severe thunderstorms, will herald the arrival of the heated domain in the Great Lakes and Mid-Atlantic region within 72 hours. The 100 deg F isotherm will, at its farthest north passage, reach very near Minneapolis MN, Chicago IL, Columbus OH, and Philadelphia PA over the course of the next four days before the subtropical high begins to weaken.

....While Strong Cool Intrusion Arrives Over The Upper Midwest By Midweek

As hot as the ridge complex across the U.S. appears, the change to a cooler pattern over the eastern portion of the continent is already underway. A series of shortwaves entering western Canada should drop steadily to the southeast, carving out a mean 500MB trough from Quebec into lower Appalachia within a week from today. Two cold fronts will introduce risks of severe thunderstorms, and then lower temperatures, into the Midwest and Eastern Seaboard on Tuesday and Wednesday.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)


How Much Of A Cool-Down In The Eastern Half Of U.S.?

There is some disagreement between the American and European versions (and the respective ensembles) concerning the strength of the polar intrusion into the eastern U.S. later in the coming week. The 12z GFS model run would suggest somewhat of an average drop in temperature for August, while the concurrent operational ECMWF seems to be pointing toward a sharper fall of values with a closed 500MB low passing through the Great Lakes and Northeast. With a prominent +PNA signature through most of western Canada, the chillier solution is favored.

Subtropical High Holds On Over Parts Of The Great Plains And Deep South

Judging by the mean 500MB forecasts of the ECMWF and GFS model suites, there will be sharp temperature differentials across North America in the 6 - 10 day time frame. While much cooler air will likely dominate the eastern half of the nation, the presence of the lingering heat ridge (and anticyclonic axis into the Prairie Provinces) implies that heat will be an issue for the Deep South, Great Plains, and Rocky Mountains through the next ten days. The West Coast, meanwhile, faces encroachment from a strong cold front, and many locations west of the Continental Divide are facing lower than normal values for August.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)


Blend Of 1976 And 1993 Summer Analogues Still Appear To Be The Most Viable


The month of August is upon us, and we can follow two lines of thought concerning how temperature and precipitation: the early stages of a weak El Nino episode following the decline of a La Nina signature (as in 1976), or an essentially neutral ENSO configuration that was accompanied by excessive rainfall in the Midwest with bursts of heat over the Eastern Seaboard (1993). If you blend the two patterns together, you come up with an August where the heat is concentrated over the Great Plains and parts of the Deep South, with cool anomalies over the West and the Atlantic Coastal Plain. Some deviations from this arithmetic average are probable, however, if one considers current trends in the numerical models. I will argue for better potential of tropical cyclone landfall along the southern and eastern coastlines of the U.S., with warmer readings over the Intermountain Regions east of the Continental Divide.

Developing El Nino Implies That "Cape Verde Season" Will End First Week Of September


The warming of the equatorial Pacific Ocean continues at the slow pace established in spring, and it would appear that a weak "El Nino" episode should soon be designated. It is known that during +ENSO periods, low latitude west and southwest flow often develops during the last three weeks of summer, creating a highly sheared environment that is highly unfavorable to tropical cyclone development across the central and eastern Atlantic Basin. With the coming change in mind (and the approach of southern-focused westerly winds and TUTT signatures are readily apparent on GOES_WEST imagery), the next three weeks will probably have the highest burst of "Cape Verde" storms. The arrival of the first week of September should see the best potential for warm-core cyclogenesis shift to the Gulf of Mexico, western Caribbean Sea, and waters adjacent to and over the Gulf Stream.


Prepared by Meteorologist LARRY COSGROVE on
Saturday, August 2, 2008 at 5:15 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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