Heavy Rain and Flash Flooding in the West; Heat Expands in the Central U.S.

Monsoonal moisture will produce showers and thunderstorms with heavy rain over parts of the Southwest, Great Basin, and Central Rockies through Monday. Flash flooding is possible, especially in and around burn scars and in areas of steep terrain. Heat will persist across the Central U.S. early this week, spreading into the Ohio Valley and Mid-Atlantic later this week. Read More >

Event Summary Graphic

Overview
Storm Reports
Radar
Environment
Additional Info

Overview

Explosive thunderstorm development occurred just after 4 PM on 8/27 over Boone and McHenry counties in an extremely unstable airmass. Temperatures at the time were in the mid to upper 90s, with dewpoints in the upper 70s.

Thunderstorm cloud tops reached 60,000 feet at times, with the strongest storms producing damaging downburst winds and hail over 2 inches in diameter.

This was the culmination of a 2-day stretch of oppressive heat and humidity. Peak heat index readings of 105 to 120 degrees were observed.

Storm Reports

Preliminary Map of Storm Reports

Preliminary Storm Report Map

Preliminary National Storm Reports

Interactive Map of Preliminary Storm Reports

Radar

Rainfall Map/Graphic

6-hour radar loop (4 PM - 10 PM). Storms after 10 PM were sub-severe.

Environment


Convective Available Potential Energy (CAPE), or a measure of "fuel" for thunderstorms at 5 PM. Values above 4,000 J/kg are supportive of explosive thunderstorm development.	Wind shear, or change of wind direction and speed from the surface to about 20,000 feet. Values are generally below 30 knots which is not particularly supportive of supercell (rotating) storms.	Microburst composite parameter, which highlights regions favorable for intense microbursts/downbursts. Values were exceptionally high over northern and central Illinois.

Additional Information

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Heavy Rain and Flash Flooding in the West; Heat Expands in the Central U.S.

August 27, 2024: Stretch of Oppressive Heat Ends with Severe Storms