WEATHERAmerica Newsletter, Saturday, May 4, 2024; MEDIUM RANGE OUTLOOK

[Larry Cosgrove]

MEDIUM RANGE OUTLOOK

(Four To Ten Days From Now)

 

Cool Intrusion Across The Eastern Half Of The USA May Be Preceded By Yet Another Severe Thunderstorm Event

UQAM Meteocentre (4)

TwisterData.Com (4)

PivotalWeather.Com (4)

College Of Dupage Weather Laboratory

Yet another severe weather outbreak is probable from the middle and lower Mississippi River watershed all the way to the East Coast. The coldness of the atmosphere in the trough associated with the surface low pressure will be forced south and eastward. Cyclogenesis in Iowa will translate eastward, likely passing through the Mid-Atlantic next weekend. Unlike its immediate predecessor, the cold front will likely reach the Gulf of Mexico on Sunday, creating a collapse of the deep tropical air mass across Dixie, The Ohio Valley, and the entire Eastern Seaboard. The addition of energy and the impressive cold advection against a cT/mTw convergence has a textbook intense convection case written all over it, and I suspect that the thunderstorms with hail and tornado threats may get into the Interstate 80 corridor before the cP air mass sweeps through by next Sunday.

Quick Moderation In Temperatures As New Storms Take Shape In The "Four Corners" And Great Lakes Region

ECMWF (4)

TrueWx.Com (4)

I would term the drop in temperature over the eastern two-thirds next weekend "refreshing". After all, some locations in the Great Plains and Midwest could see record low readings at night. And parts of Texas and the Dixie states could get a reprieve from high humidity and be able to turn off air condition units. But as with any case of a polar intrusion in May, the chill cannot last. Sun angle is one consideration in rising thermal values. Another is the upper atmospheric set-up.

You will note the formation of a closed low aloft over the Southwest, likely one of the last inputs from the elongated storm sequence that stretches from Tibert to North America. At some point, probably in the third week of this month, the last disturbance will slow and stall across the West, forming a 500MB trough that shifts winds to the southwest from Mexico into Appalachia. This process is hinted at by the ECMWF and GGEM series, and would mean a cool West/warm East alignment. A cold low will section off over the Prairie Provinces and then the Great Lakes by May 14, perhaps setting up thunderstorm threats in the Upper Midwest and Ohio Valley. Meanwhile, the south central and Southeast states will start to warm up a bit day-by-day, and the jackets will be put away until the fall arrives.