WEATHERAmerica Newsletter, Sunday, July 12, 2026; SHORT And MEDIUM RANGE OUTLOOKS

[Larry Cosgrove]

SHORT RANGE OUTLOOK

(Through The Next 72 Hours)

 

Lateral Heat Ridge Extends (Briefly) Into Ohio Valley, Mid-Atlantic

METEOBLUE

PivotalWeather.Com (3)

ECMWF

College Of DuPage Weather Laboratory

 

There is the matter of a lateral heat ridge with roots in the Desert and Intermountain Regions. This ridging will, for a time, extend a finger into the Midwest and later the Mid-Atlantic states. If so, the potential for meaningful, if not strong, cooling demand along the Interstate 70 and 80 corridors may increase late in the new week. There could be complications from thunderstorms, but the subsident nature of the subtropical high will likely limit clouds and rainfall, something seen on the latest NAM projections from the Front Range into southern New England to the Mason-Dixon Line.

Most of the deep tropical moisture will be derived from the monsoonal fetch over Mexico, making a relatively minor appearance in the Desert Southwest. The chances for heavy thunderstorms (only a few severe) will be high from the Sonoran Desert eastward through Texas and most of the Old South during the near term. Note the broad 500MB weakness below the ridge which will enhance diurnal and seabreeze convection.

MEDIUM RANGE OUTLOOK

(Four To Ten Days From Now)

 

Western/Central USA Heat Ridge, 500MB Weakness From The Gulf Of Mexico To Ontario/Quebec Is Mostly A Hot Pattern West Of The Mississippi River

METEOBLUE

ECMWF (4)

UQAM Meteocentre (4)

TrueWx.Com (4)

College Of DuPage Weather Laboratory

The 500MB gradient flow between a Hudson Bay Low and the rebuilding heat ridge over the western and central USA will be a sort of dividing line, separating hot and humid conditions vs. a polar air mass across southern Canada into the Mid-Atlantic states. This type of set-up was seen in the summer of 1976, with repeated thunderstorm chances across the Midwest into the Eastern Seaboard. Whereas the convection with a weakness across roughly the southern third of the USA will be diurnal and "pop up" in nature, severe weather (especially microbursts) will be a growing concern between the Interstate 70, 80 and 90 corridors. Some of the schemes also bring monsoonal-related showers and thunderstorms across parts of the Desert and Intermountain Regions during the medium range. In any event, the high moisture profiles of the atmosphere may keep many readings below 100 deg F due to clouds and precipitation well south of the frontal structure.