WEATHERAmerica Newsletter, MEDIUM RANGE OUTLOOK; Saturday, August 23, 2025

[Larry Cosgrove]

MEDIUM RANGE OUTLOOK

(Four To Ten Days From Now)

 

The Polar Air Mass May Look Impressive....

ECMWF (4)

PivotalWeather.Com (4)

Sections of the Great Plains, Midwest, Great Lakes and the Northeast are going to get another dose of polar air early in this period. The release of the cPk domain (not Arctic, by the way....) will likely be accompanied by intense thunderstorms, followed by some spectacular weather with low dewpoints and cool, fair nights more reminiscent of mid-Autumn than early September. But note the stubborn heat in the southern tier of the nation, which starts making gains into the Great Plains again (albeit briefly) by next weekend. Southwest flow ahead of the cool intrusion will create opportunities for showers and thunderstorms, with warm ridging in western Canada still setting up northwest flow that runs into warm, muggy, unstable air.

....But Moderation (From Canada) Will Soon Follow! And Maybe A Tropical Cyclone, Too!

UQAM Meteocentre (4)

TrueWx.Com (4)

TwisterData.Com (4)

College Of DuPage Weather Laboratory

The second cold frontal penetration through the eastern two-thirds of the lower 48 states will have the same characteristics as the first. The boundary may stop along the Interstate 20 corridor, keeping much of Texas and the Deep South in heat and high humidity. Thunderstorm threats will continue across the Desert and Intermountain Regions as well as the Gulf Coast and Florida Peninsula. Cooler values will immediately be felt in the Great Lakes and the Northeast, possibly involving the Mid-South as well. But duration of cPk regimes in late summer is typically not long-lasting, and warm recovery should be evident in most of the affected areas by September 2-3.

Do not disregard the threat to the Caribbean Sea/Greater Antilles late in this time frame. The GFS and GGEM panels show a Gulf of Mexico system at 240 hours, and the ECMWF panels have a good deal of convective rainfall moving out of the tropical Atlantic Basin into the Gulf Coast with a broad weak trough across the eastern third of the lower 48 states. This is a recipe for a prominent weather event, since the Gulf of Mexico waters are very warm and shearing wind profiles will diminish as the trough complex becomes diffuse. In any event, if there is an important storm, the 11-15 day period in Texas and the Deep South is the most likely risk zone.