Severe thunderstorm risk increasing across far northern Illinois Thursday afternoon

CHICAGO — It’s another hot, steamy afternoon across Chicagoland, priming the area for a new round of thunderstorms.

With temps approaching 90 degrees, and dew points ranging from the upper 60s to mid 70s, the atmosphere has become very unstable.

Radar shows a line of strong to severe storms in an arcing line from northern Wisconsin to northeast Iowa. This line has a history of producing 1 inch diameter hail, and wind gusts in excess of 70 mph.

The above map displays a measure of atmospheric instability. The higher the values, the more unstable the air. With very unstable air feeding into the line to our northwest, it is likely that these storms will continue to develop east-southeastward during the afternoon.

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For more details, see the SPC discussion below:

Mesoscale Discussion 1272
NWS Storm Prediction Center Norman OK
0155 PM CDT Thu Jun 27 2019

DISCUSSION…A linear MCS currently extends from central WI
southwestward into northeast IA, progressing eastward at about 30-35
kt. Some modest sharpening of the reflectivity gradient along the
leading edge has occurred over the past hour or so. At the same
time, updraft strength and echo tops have remained fairly
consistent.

A gradient exists within the low-level moisture ahead of the MCS,
with dewpoints in the 70s across northeast IA decreasing to the mid
60s across central IA. This moisture gradient leads to a gradient
within the analyzed instability, with 3000 J/kg of MLCAPE estimated
over northeast IA decreasing to less than 1000 J/kg over central WI.
This gradient will likely provide a favored path of progression for
the MCS, suggesting continued southeastward motion.


The approaching storms will most likely affect areas generally along and north of I-88 late this afternoon or early this evening.

 

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