A TORNADO WATCH has been issued for Stephenson, Carroll and Jo Daviess counties in northwest Illinois, and for Green and Rock counties in south-central Wisconsin until Midnight.
The first round of thunderstorms produced only isolated strong/severe wind gusts Wednesday afternoon as it moved through most of the region, weakening as it moved further east running into a little more of a stable environment. While the skies were cloudy ahead of the first line, some clearing has been taking place further to the west, and this has allowed the atmosphere to ‘recover’ a bit, building back up in the instability with rising temperatures and dew points across northeast Iowa and northwest Illinois.
Supercell thunderstorms were quick to develop in north-central Iowa Wednesday evening where numerous tornado warnings were issued. Those storms will continue to move through northeast Iowa and towards southwest Wisconsin this evening, still posing the risk tornadoes and damaging winds/large hail. Even though we are a couple hours away from sunset, the low level jet will be increasing (lower winds in the atmosphere) feeding more moisture into the area. This combined with a stout upper level disturbance will help to maintain some risk of severe weather through the overnight. As the storms currently over northeast Iowa move east and northeast, they should begin to form more into a line, or cluster, of storms. This could pose more of a wind threat downstream of where the current watch has been issued.
Thunderstorms could be moving into far northwest Illinois as early as 9pm or 9:30pm, but most likely pushing east through the area between 11pm and Midnight. As these line of storms continue there may be just enough instability in the atmosphere to help maintain the risk for some stronger winds gusts, as well as an isolated tornado. Heavy rain will also be a concern with these storms tonight, into Thursday morning.
Make sure you have multiple ways to receive watches and warnings, especially as these storms are expected to move in after dark.