Snow Across the Great Lakes, Central Appalachians, and Northeast; Unsettled Weather in the West

Light to moderate snow will continue into Saturday over the Great Lakes, Central Appalachians, and Northeast. This weekend into next week, a series of atmospheric rivers will bring gusty winds, periods of heavy rain, and mountain snow to northern California and the Pacific Northwest. Colder temperatures are in store for the weekend from the Great Lakes to East Coast. 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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Snow Across the Great Lakes, Central Appalachians, and Northeast; Unsettled Weather in the West

Stretch of Oppressive Heat Ends with Severe Storms