WEATHERAmerica Newsletter; Saturday, July 5, 2025; SHORT RANGE OUTLOOK

[Larry Cosgrove]

SHORT RANGE OUTLOOK

(Through The Next 72 Hours)

 

Monsoonal Weakness Separates Cooler, Very Moist Regime from Widespread Heat And Humidity; Thunderstorm Threats Result

METEOBLUE

UQAM Meteocentre (3)

TwisterData.Com (3)

University Of Wisconsin Weather Server (3)

College Of DuPage Weather Laboratory

After the tragedy of flooding thunderstorms in Kerr and Burnet counties in Texas this weekend,  I can cite from memory that forecasting such events (small mesoscale) are deeply problematic. The Big Thompson Canyon (CO), Johnstown PA (II), and Brush Creek/Plaza Kansas City KS/MO floods in 1976 and 1977 all stand out as so-called "100 year happenings" that were not predicted well, claimed lots of lives and triggered lots of excuses as to "why". Just consider that all such floods occured when a convergence of factors happened to come together at the same time. Local warnings did not hit hard enough either in terms of time frame or impact. Cities did not have a reliable method to warn the public. MCC formation and subsequent slow motion in a 500MB weakness with an established cTw vs. mTw surface boundary dumped torrential rain (15-20") on a river surrounded by hard, dry soils that allowed for fast runoff. And there were homes and cabins in the floodplain adjacent to the streams and rivers.

Useless incriminations aside, we need to look at the future. The cleavage between the Sonoran and heat ridge and Bermuda High is still over Texas, and likely will be there through Tuesday. Other convective groupings could develop, perhaps even across the lower Interstate 35 corridor. Of greater worry is the motion of the dry line into the Great Plains, with a new cold low at 500MB. Severe weather and excessive rainfall is probable from North Dakota southward to the Red River Valley (TX/OK) over the next 48 hours, reaching the Mississippi Valley and lower Great Lakes. Tropical Storm Chantal may set off some strong thunderstorms in the Carolinas before shear and southwest flow aloft carry its remnants out to sea. There will also be diurnal+orographic convection along the New Mexico and Colorado Front Range in the near term.

Bottom line: there are lots of dangers in weather coming up. 

Heat Surge Over Parts Of The West Due To Sonoran Ridge Complex

METEOBLUE

PivotalWeather.Com (3)

ECMWF

Sonoran heat ridges are common in July, even precedent to a monsoon expansion. For the next week or so the subtropical high will deep fry the Desert and Intermountain Regions, then start to expand/slide eastward in an attempt to merge with the even larger Bermuda High. An upper low off of the California shoreline may induce some marine layer presence into major cities, but another shortwave in the polar jet stream should force pronounced cTw advection eastward. This could turn out to be one of the hottest weeks of 2025, since a dry air insertion into the mid-levels may end the grouped convection threat in the south central states.