WEATHERAmerica Newsletter, Saturday, June 28, 2008 at 6:45 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)
MI....WI....IL....IN....OH....WV....KY....TN....NC....SC....GA....FL....AL....MS....LA
AR....TX....NM....CO

SCATTERED Severe Thunderstorms
(Microbursts, Large Hail, Isolated Tornadoes)
VA....DC....MD....DE....PA....NJ....NY....QB Eastern Townships

Some Thunderstorms May APPROACH Severe Limits
E ON....C QB....N ME....NB


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

Scattered Locations In
E ON....C QB....N ME....NB
(QPF 1 - 3")

Scattered Locations In
VA....DC....MD....DE....PA....NJ....NY....QB Eastern Townships
(QPF 1 - 3")

Isolated Locations In
MI....WI....IL....IN....OH....WV....KY....TN....NC....SC....GA....FL....AL....MS....LA
AR....TX....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
SW SK....S AB....S BC....WA....OR....CA....NV....ID....MT....WY....CO....W KS
OK Panhandle....W TX....NM....AZ

Scattered Locations In
FL....SE GA....SC....C, E NC....C, E VA....DC....MD....DE....SE PA....NJ....NYC NY

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, A Cool Intrusion For Midwest And (Eventually) The Eastern Seaboard....

Considering that none of the numerical models saw a digging trough over Pennsylvania and Maryland early next week, the trend toward heavy, prolonged precipitation followed by widespread cooling is somewhat of a surprise. Since a strong, persistent Bermuda High is offshore, much of the cooler air mass will moderate by the time it reaches the Atlantic Coastal Plain. All this after perhaps three days of heavy to severe thunderstorms that may reach as far south as Georgia and to Maine and New Brunswick to the north.

....While Fires, Heat, And Drought Grip The Intermountain Region

While cooler air may reach parts of the currently heated Pacific Northwest within 48 hours (courtesy of a shift in the ridge complex across the Intermountain Region), an area from California into the Front Range and Great Plains will feel the full fury of the summer sun. With a weakness setting up between the Mississippi River and Appalachian Mountains, downslope and compressed flow of hot and dry air will take hold of most locations from Montana and the Dakotas into Texas and Louisiana in the near term.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

High Heat Across Parts Of The West, Great Plains, And Old South

Summer heat may be missing (for now...) in the Midwest and Northeast, but that will surely not be the case across the Intermountain Region, lower Great Plains and parts of the Old South by late next week. The center of the Sonoran heat ridge is forecast to shift to near Denver CO, which will allow for some cooling over the Pacific Northwest while keeping California exceptionally torrid. Another bracket of dangerously hot conditions should begin to emerge from Kansas into Texas by July 5, perhaps offset further east by the presence of deep tropical moisture.

Cool Fronts May Continue To Plow Through The Great Lakes And Northeast

Although increasingly weaker during the medium range, most of the numerical models show at least two more frontal passages through the Great Lakes and Northeast. Falling in the gap between the strong Sonoran and Bermudan heat ridges, these fronts will be able to tap a great amount of tropical moisture from the Gulf of Mexico. The end result of the intrusions of cooler air will be thunderstorms, some severe, occurring with frequency from the Upper Midwest into most points along the Atlantic Coastal Plain above the Virginia-North Carolina border.

Potential For Tropical Disturbance Affecting The Western Gulf Coast?

Alone among the numerical models, but consistent in its presentation, the ECMWF scheme shows the approach of a tropical disturbance to Texas and Louisiana, apparently undeveloped due to shear and/or dry air infiltration. Moving into the weakness between the Bermuda High and Sonoran heat ridge, the disturbance may bring needed rainfall (and lower temperatures) to the western Gulf Coast during the July 6 - 8 time frame.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

Teleconnections On Systems And SSTs In The Pacific Basin


Part of the reason that the winter and spring of 2008 featured so many storms and radical temperature shifts as the connection of deep tropical moisture and energy with the polar westerlies across eastern Asia and the western Pacific Ocean. After a three week interruption, that linkage is back and threatening to alter the forecast landscape over North America for the summer season. A weak El Nino episode is taking shape over the equatorial Pacific Basin, while water temperatures continue to warm over the Gulf of Alaska and off of the West Coast (putting to lie the claims of a lasting negative display of the Pacific Decadal Oscillation, but that is a discussion for another day...). The effect of the jet stream configuration (with three vigorous disturbances) combined with a tendency for ridging of a +PNA signature, is for a deeper, active trough over the Upper Midwest and Great Lakes. With a weakness between the Sonoran heat ridge and Bermuda High popping up from time to time, the transport of tropical moisture creates a cooler, wetter scenario than was thought earlier from the upper Mississippi Valley into the interior Northeast. Due to the stronger ridging over the western Atlantic Basin, a warmer prediction emerges from southern New England through the Mid-Atlantic states.


Any Useful Analogues For The Summer Of 2008?




With the massive amounts of thunderstorms and rain across the Midwest this spring and summer, much has been made about a possible tie to the weather of the warm season of 1993, which also saw record amounts of rainfall and severe storms. The developing El Nino episode in the equatorial Pacific Basin, together with an active polar front progression across the Great Lakes and Northeast, has drawn comparisons to the June-September configuration of 1976, which saw numerous frontal passages and frequent strong convection. But to these analogues really tell us anything about current, and future, forecast possibilities in the U.S.?

Perhaps, but temperature comparisons for the first three and a half weeks in June will get the synoptician positively nowhere! As readers of this newsletter know, I am not a fan of over doing comparisons of either climatic indices or absolute atmospheric parameters (such as 500MB or surface weather type). To prove the wisdom in this policy, check out the readings for this year vs. the two other terms. There is only the slightest resemblance in values to those seen 15 years ago, and almost an inverse to that seen in the bicentennial year! This is not to say that the remainder of this summer will not resemble either case; indeed, if you consider that the GFS version shows four cold front tracks through the Great Lakes and Northeast, the 32 year old 500MB longwave pattern may be somewhat viable as a guide for what lies ahead.

But take it from someone who has been actively predicting weather since that landmark summer and winter that marked two centuries of American independence. All the indices and analogues out there, in the end, will tell you very little about what plays out between now and some future time (hint to all of you winter weather enthusiasts....). But sometimes, that small amount of insight is all we have to go on in making a longer range prediction.

Prepared by Meteorologist LARRY COSGROVE on
Saturday, June 28, 2008 at 6:45 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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