MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
Summing Up The Weather Across The U.S.: Brutal Heat, Humidity In the Great Plains And Old South, With Thunderstorms Everywhere Else
Plymouth State University Weather Server
I could call the forecast for the period August 3 – 9 as “ridiculously easy” or “redundant”, given its very repetitive nature. But the outlook is actually worrisome on three scenarios. One is the likely track of Invest 91L (very likely into the open Atlantic Ocean after visiting Puerto Rico, but could interact with a shortwave and cold front moving into the East Coast around August 8). Another is the power of a 500MB heat ridge that could continue extreme heat and smog over the central and southern reaches of the nation. Thirdly, there is a danger of derecho formation across the northern tier of the U.S. as prominent impulses progress along in the semizonal flow. If you drew an arc from MT and WY into the Great Lakes and Mid-Atlantic states, that would be the target zone for prominent convection carrying hail, high wind, and isolated tornado threats.
The Pacific Northwest and New England should stay out of the heat, which will make occasional inroads into the Corn Belt, Dixie and even the Eastern Seaboard. On the idea that the operational GFS and ECMWF schemes are too far west with the core of the subtropical high (which has been the case since May 27), the active monsoon should allow for more tolerable temperatures in the Desert Southwest and Rocky Mountains. As for the Great Plains and much of the Mississippi River watershed, however, the 2011 “Hell On Earth” tour continues to play on.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
“Breaking Up An Entrenched 500MB Longwave Pattern Is So Very Hard To Do”; -PNA Configuration Hold On, With Hot Weather East Of The Rocky Mountains, Through At Least August 15 (And Probably Through The Labor Day Weekend)
University Of Nebraska/HPCC
Penn State University E-Wall
Contrary to what some sources have been reporting, this has been a hot summer in the Midwest. Also, the Northeast and, of course, the Great Plains into Texas. You can call the season cool over the locations to the left of the Continental Divide, and perhaps normal over sections of the Southeast (due to frequent diurnal convection). But, barring a sudden display of cooler values in August, the 2011 “Hell On Earth” will likely be within the Top 5 hottest summers of all time.
Reviewing the numerical models, I see little change in the jet stream configuration during the extended period, and very likely into the Labor Day weekend. The ensemble members of the GFS equation actually shift the westerlies a bit higher in latitude into Canada, with more than a few members showing a resurgence of the Sonoran+Bermudan heat ridge into the Midwest and Eastern Seaboard by the middle of the new month.
Review of the set of analog years (1918, 1951, 155, 1956, 1971, 1974, 1976, 1980, 1985, 1986, 1988, 1995 (x2), 1997, 1999 (x3), 2000,a nd 2008 (x2) support some marginal cooling along the northern tier states, much like what is expected in the near term. The presence of a fairly strong negative height anomalies over the East Coast would seem to favor at least a near-miss by a tropical cyclone, with trough digging after passage of the storm. But once again, prominent heat ridging keeps a blazing sun and hellish heat across the middle and southern stretches of the U.S. in August.
The more things change….
Prepared by Meteorologist LARRY COSGROVE on
Saturday, July 30, 2011 at 5:40 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 2011 by Larry Cosgrove
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