TODAY’S FUN LINK: CIMSS Tropical Cyclones
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)
GA….SC….NC….VA….DC….MD….DE….PA….NJ….C, E NY….CT….RI….MA….VT
ISOLATED Severe Thunderstorms
(Microbursts, Large Hail)
Ranges Of CO, NM
Some Thunderstorms May APPROACH Severe Limits
ISOLATED Severe Thunderstorms
(Microbursts, large Hail, Isolated Tornadoes)
WA….OR….ID….W MT….S BC
HEAVY RAINFALL OUTLOOK
(potential for an inch or more total rainfall within the next 24 hours)
Isolated Locations In
GA….SC….NC….E TN….E KY….VA….DC….MD….DE….E PA….NJ….C, E NY….CT
(QPF 1 – 2″)
EXCESSIVE HEAT OUTLOOK
(potential for temperatures above 95 deg F)
S, C CA Deserts….C, S NV….AZ….UT….WY….CO….NM….TX….NW LA
AR….OK….C, S KS….SW NE
GLOBAL WEATHER SUMMARY
(a review of important weather features around the world)
Monsoonal moisture is the feature to watch, as the fetch is responsible for two important aspects of sensible weather. One is the steady stream of dewpoints, with showers and thunderstorms, into central China and Mongolia. This gives hope that recent drought conditions in the PRC will soon be history. Secondly, and most importantly for North America, inflow from the monsoon is setting off a firehose polar jet stream that cuts in a semizonal fashion across the entire Northern Pacific Ocean. Teleconnections on this abnormally strong band of westerlies favor a) low potential in the near term for typhoon development and b) long-lived displays of heat over the southern two-thirds of the U.S. with repeated MCC and derecho development along the American north tier and adjacent Canadian locations.
Strong polar westerlies continue into the Pacific northwest, wrapping around an impressive mPk vortex in the Gulf of Alaska. Note that the northern branch is beginning to move across southern Canada, favoring intense warm advection over much of the lower 48 states. See also that upper westerlies are in place to the right of the International Dateline, with prominent TUTT signatures southeast of Hawaii and encompassing much of Mexico.
Thunderstorms dominate the northern third of the U.S. and southernmost Canada, as polar westerlies begin to inch along the international border. This zone will be a hot spot for severe weather and excessive rainfall over the next two weeks. Upper flow is distinctly southwest over much of the tropical Atlantic Basin, the notable exception being the lower Caribbean Sea. A subtropical disturbance is seen across the Sargasso Sea.
There are four relatively weak disturbances in the ITCZ across equatorial Africa, but once again upper level southwest flow is creating a shearing environment and funneling moisture toward Europe and the Arabian Peninsula. An intense storm complex across the northern Atlantic Ocean will be targeting the British Isles and Scandinavia over the next four days, while strong ridging (with fair skies and warm weather) holds in place in the vicinity of the Ukraine.
The remnants of Tropical Storm Phet are breaking up over southern Pakistan and southwestern India. Much of the Central Asian and Indian Ocean theater is quiet, with disturbances shifting into a monsoonal phase across much of Indochina and parts of the PRC. Some convection is affecting Sri Lanka and southern tip of the Indian subcontinent.
SHORT RANGE OUTLOOK
(Through The Next 72 Hours)
Severe Weather Targets The Northeast….
University Of Wisconsin Weather Server
Risks for intense convection have been ramping up over the northern third of the U.S., and most signs point toward either a derecho or standard MCS passing through parts of the Mid-Atlantic and New England regions on late Saturday night and Sunday. Severe weather watches and warnings have been ongoing in the lower Great Lakes, and with a shortwave plowing headlong into very unstable air (core LI – 5 to -8), the fireworks may continue until the low and cold front exit the coastline on the afternoon of June 6. Note that the NAM version shows an impressive surface convergence signal and clustered increase in vertical velocities, which if verified favors a linear thunderstorm banding affecting the Interstate 90 and 80 corridors.
….With A Nice Cool Intrusion Following Through The Great Lakes And Parts Of The Eastern Seaboard
Plymouth State University Weather Server
While not a large are of cooler values, locations in much of the Midwest into New England and the Mid-Atlantic states will get a refreshing breather from heat and humidity, as well as the threat for rain and thunder. Once the 500MB shortwave passes offshore, a cP regime should infiltrate as far south as the Interstate 40 corridor (Memphis TN to Wilmington NC) by Monday morning. I do not expect this cool domain to last very long (48 to 72 hours), but the effects will be appreciated by a public that probably knows what is coming in the medium range!
Heat In Lower Great Plains, Severe Thunderstorm Concerns In The Midwest!
Plymouth State University Weather Server
If you look closely at the GOES WEST image provided, you can see a very well-defined storm approaching the Pacific Northwest. This system is a relatively slow mover, but will have impacts from rain and thunder during Sunday as the center pushes toward BC and WA. I expect some deepening of the trough complex, enabling the mP values to reach as far south as S CA. But it is when the polar air reaches the northern/central High Plains that some dramatic turns in sensible weather will occur.
There is impressive agreement among the numerical models concerning the evolution of convective threats on Monday night and Tuesday. As the surface warm front reforms and moves to an Omaha NE to Paducah KY line, thunderstorms will fire and move east-southeast along the thermal boundary. If you examine the GFS, GGEM, and ECMWF outlooks, the situation practically shouts “derecho”. The threat for a severe weather + flooding rain event will be greatest in a polygon bounded by Benkelman NE….Sioux Falls SD…..Joliet IL….Owensboro KY. If a “right turn” scenario emerges (entirely possible with the heat ridge building over Oklahoma), then either the Ohio/Mississippi River confluence or the Tennessee Valley will be at risk for a particularly potent outbreak of large hail, microbursts, tornadoes, and torrential rainfall.
MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
-PNA Configuration Practically Screams Cool West, Hot East Of Rocky Mountains
Plymouth State University Weather Server
With a rather vigorous polar jet stream driving disturbances into the Pacific Northwest, teleconnections are lining up for a trough West/ridge Center/East alignment that may continue through much of the extended period. With a trough complex occupying the Intermountain Region, the Sonoran heat ridge will be kicked into the Great Plains. The most obvious result will be an expansion of the cT regime into the Midwest and Old South. most of the computer models are generous with the northward shift of the hottest air (somewhere close to an Interstate 90 line seems plausible, at least west of NY State).
A problem occurs with the operational 12z GFS scheme and the ensemble members of the GGEM equation. Both versions suggest a much stronger cool push through the Midwest into the Eastern Seaboard during and after June 13. However, the ECMWF model suite and GFS variants are in wide disparity with the other outlooks, hinting at a long-lived hot spell for most communities from the Front Range to much of the Atlantic Coastal Plain. There is some room in the 500MB longwave pattern for a backdoor cold frontal passage in the Northeast, but it seems likely that many communities outside of the West are in for a lot of heat over a long time.
Severe Weather Potential Shifts To Northern Third Of U.S.
Because the subtropical high will lurch northward into the Missouri and Mississippi Valleys, the threats for intense convection will likely relocate further to the north as well. Following the ECMWF model suite/GFS ensemble scenario, the best potential for strong to severe thunderstorms will likely be in the High Plains and along the northern tier of the nation. Note that despite its very aggressive cold frontal depiction, the standard American version has its most impressive precipitation output over MT, WY and the Dakotas. Because of the presence of the fast semizonal flow along the Canadian border, MCS and even derecho formation seems probable with a lack of a well-defined mid-latitude cyclone.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
Will Surge Of Hot Air Relax? Somewhat, But Not A Lot
Penn State University Weather Server
I would not count on a major cooling trend setting in soon across the eastern two-thirds of the U.S. When you factor the evolving La Nina episode, the statistical+dynamic numerical models (such as the NAEFS package), and the noticeable -PNA trend seen so far in the spring, any reduction in tropical air masses looks to be minor. What could cut into the prevalence of hot air would be any warm-core cyclone or TUTT signature, provided the ridge complex shifted far enough to the east off of the Atlantic coastline. Unfortunately, all but the GGEM panels agree on periods of high heat in locations east of the Rocky Mountains. I do buy into a brief relaxation in the cTw+mT regime in the Great Lakes and Northeast at the start of the longer term, but suspect that the 100 deg F isotherm will be in the Corn Belt by June 21.
While the potential for a tropical wave moving through the Caribbean Sea and moving into the Gulf of Mexico is likely bogus (the upper air charts are not supportive, and nothing shows up on current satellite data that would suggest such a system organizing and moving west and north), it is always a good idea to keep an eye on even the smallest system. Because we are now into Hurricane Season, and past examples abound of “surprise” storms.
Upper Level Winds Hold Clues About Tropical Cyclone Potential, Heat Threats
Even someone giving a cursory look at the MTSAT and GOES WEST satellite images would have to recognize the rather bizarre appearance of a “firehose” jet stream that stretches from the Orient into the Pacific Northwest. Typically such tight, intense stretches of polar westerlies occur in the middle of winter, and when they occur signify either an a) very mild, dry trend across the lower 48 states or b) +PNA configuration that keeps the eastern half of the U.S. chilly and wet (but rarely cold and snowy). In the case of summer, the “dumping” of the energy into a -PNA signature (trough West) almost always yields a very hot pattern with a unique Sonoran +Great Smokies heat ridge. Very similar to what was seen in 1995 and 1998.
To the tropical weather enthusiasts, another kind of high-latitude westerlies are keeping the threat of warm-core cyclogenesis quite low. Note that strands of high cirrus are visible on most bands of satellite imagery from near the International dateline all the way into the Horn of Africa. So while occasionally some impressive waves may form along the ITCZ and move westward (with a nice stretch of warm water over the equatorial Atlantic Ocean, thank you), the presence of shearing flow at high altitudes prevents any long-lasting formation of convective circulations from occurring. While it is difficult to say just when the strands of southwest flow aloft will go away, the fact that it is early June suggests that some time will needed before deep mean easterlies can develop and allow for outflow and congealment issues to improve.
Prepared by Meteorologist LARRY COSGROVE on
June 5, 2010 at 5:15 P.M. CT
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 2010 by Larry Cosgrove
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