WEATHERAmerica Newsletter, Saturday, June 22, 2024; MEDIUM RANGE OUTLOOK

[Larry Cosgrove]

MEDIUM RANGE OUTLOOK

(Four To Ten Days From Now)

 

The Big Heat Ridge Is Destined To Stick Around

ECMWF (4)

PivotalWeather.Com (4)

The thorn-in-your-side subtropical high may have occasional dents due to shortwaves riding to its north and the thunderstorm-induced cool intrusion. But the two cores of the ridge complex will survive each alteration, and likely bounce back stronger than before. Case in point is next weekend, when a particularly intense storm and frontal couplet pass through the northern tier of the USA, with convective emphasis on the Great Lakes and the Northeast. Compression of the positive 500MB height anomaly will produce incredibly hot air across the south central states, with some spread through the Desert Regions and the Mid-Atlantic and Southeast. In time, the cTw+mT air mass will return to locations above 40 N Latitude.

Severe Weather Likely Either Side Of The Canadian Border; Cool Intrusions Most Likely Stay In The Pacific Northwest And The Northeast

UQAM Meteocentre (4)

TwisterData.Com (4)

TrueWx.Com (4)

College Of DuPage Weather Laboratory

Let me make this very simple. If you live along or above Interstate 90 (Seattle WA to Boston MA), pay close attention to severe weather outlooks, watches and warnings in the days leading up to July 4th holiday. This is going to be a rough go.

What is telling is the dry area in the south central states. That is a marker for a cTw air mass, which, along with the humid/buoyant regime off of the Gulf of Mexico, will be drawn into a powerful series of shortwaves emanating form the Gulf of Alaska Low. Each disturbance will be accompanied by a frontal stricture, with impressive forcing/lifting amidst surface convergence of the air masses. Timing may be a bit difficult, but generally every two to three days you will see an event of outbreak of particularly intense convection in either singular/discrete or linear (QLCS or potential derecho formation) thunderstorms that blast through at high rates of speed. That is the caused by the presence of a fast semizonal flow above the heat ridge complex. 

Also watch for thunderstorms in Mexico, which I suspect are the prelude to an active monsoon season over the Desert and Intermountain Region by the middle of July.