WEATHERAmerica Newsletter; Saturday, July 19, 2025; MEDIUM RANGE OUTLOOK

[Larry Cosgrove]

MEDIUM RANGE OUTLOOK

(Four To Ten Days From Now)

 

Major Heat Wave From Rocky Mountains To Appalachia

ECMWF (4)

PivotalWeather.Com (4)

As I have stated more times than I care to remember, when two strong subtropical highs merge, a long, intense period of hot weather will take over in a large part of the lower 48 states. There may be a brief trans-ridge gap that emerges over the Gulf Stream, or later Appalachia, but this system looks like one of the more intense heat ridges in recent history. Bounded by a monsoonal moisture fetch on the West, a frontal structure close to the Canadian border, and a northwest flow from Ontario that occurs occasionally and runs through the Northeast, the ridge complex will act to dry out Texas and Mexico, thus opening a stagnant heat source that should occupy The Lone Star State, Great Plains and Mississippi Valley, and make occasional, but never durable, inroads with hot air into the Mid-Atlantic and New England states. If a tropical feature does organize over the Gulf of Mexico in the 6-10 day range (unlikely), the capped, compressed atmosphere to the north and west of the disturbance could create a window for near-record heat along the Interstate 35 and 45 corridors (roughly KS/MO, OK/AR/TX/LA) through most of this time frame.

Cooler Temperatures, Thunderstorms Possible  In The West And Great Lakes/Northeast?

UQAM Meteocentre (4)

TrueWx.Com (4)

TwisterData.Com (4)

College Of DuPage Weather Laboratory

Despite the main emphasis of conversation being centered on the large-scale heatwave (justified), there must also be a discussion on thunderstorm potential, which I suspect is being underplayed in the media and in the weather community as a whole. Consider that the West will have bouts of very heavy rain and severe weather with the monsoonal fetch, which will pulse from near nothing to numerous convection reports and back again from the near term through the extended outlook. Some of that moisture and instability will be pulled into shortwaves edging east-southeast from British Columbia, running close to the International Border. Using climatology as a guide, this set-up is favorable for a series of MCS or derecho formations in a belt from Montana through the Dakotas, Iowa, and Minnesota, continuing through the Great Lakes and the Northeast. After a blistering hot day it i snot a good thing to experience strong/severe thunderstorms. But that's what could happen. Oddly enough, the parts of Texas hit hardest by recent rains may turn into the driest spots nationally with the heat ridge nearby.