Heat Advisory issued for a portion of the area Wednesday; Strong to severe storms set to follow

A HEAT ADVISORY has been issued for Stephenson, Jo Daviess, Carroll and Whiteside counties beginning 11am Wednesday, lasting through 10pm. 

Isolated storms are possible overnight Tuesday as thunderstorms have started to develop over southeast Minnesota.  The highest risk for strong/severe storms Tuesday night will remain just north of the immediate Stateline, but with higher instability and enough wind shear in the atmosphere overnight a few of those storms could move into southwest Wisconsin and northwest Illinois after Midnight.  The risk for severe weather would be low, but a few strong storms - should they develop - would be capable of producing gusty winds and small hail.

Moisture will continue to increase Wednesday behind a warm front that'll lie to our north during the afternoon.  This will keep dew point temperatures in the low to mid 70s for much of the day.  Isolated thunderstorms are possible throughout the afternoon as the heat builds across the area.  The combination of dew point temperatures in the 70s and air temperatures in the low 90s, the heat index for most will rise into the upper 90s and low 100s.  Wednesday will be similar to what we experienced this past Saturday with the high heat and humidity.

While isolated thunderstorms are possible during the afternoon, a slightly higher risk for strong to severe storms will be possible late Wednesday night/overnight.  Thunderstorms will develop and quickly turn severe in central Wisconsin during the afternoon and evening.  As those individual storms form into a cluster, or MCS, during the evening they'll continue to move south and southeast, entering into southeast Wisconsin around Midnight.  Depending on the exact track of the storms, and the overall position of the winds aloft steering the storms, a portion of that cluster could impact parts of the Stateline.  Areas at most risk appear to be along and east of a line stretching from Janesville to Rockford.  This is where we have a slight risk for severe storms.  An enhanced risk for severe weather resides further north in Wisconsin.

The greatest threat from storms Wednesday night would be strong, damaging wind gusts, as well as large hail.  The time line for storms entering into the Stateline would be roughly from Midnight through 4am.  It's possible that the cluster of storms could remain more to our northeast, impacting more of southeast Wisconsin, Chicago and NW Indiana.  If that's the case then most of the area would remain dry Wednesday night.

We'll know more regarding our storm risk Wednesday night once the storms develop during the afternoon in Wisconsin.  This will help us pinpoint the exact track, timing and highest risk for severe weather during the overnight.