Many of you have been wondering about the potential for severe weather Thursday evening and overnight. Especially given some of the stronger thunderstorms that moved through Tuesday night.
The highest storm threat Thursday afternoon and early evening has been well to the west over western and central Iowa. This is the area closer tied to low pressure and a cold front.
Thursday morning was mostly dry, but by mid-morning and early afternoon showers developed. Those showers actually helped form a 'mini' low pressure system, also known as an MCV (Mesoscale Convective Vortex) over northwest Illinois. This MCV helped to ignite a few showers over southern Lee and DeKalb counties during the late afternoon. Those thunderstorms are now producing flooding rainfall over the suburbs of Chicago.
Something that helps thunderstorms maintain their strength during the overnight (even with the loss of daytime heating) is the low level jet. This is a nocturnal jet stream in the lower part of the atmosphere that helps maintain moisture and instability - factors needed for thunderstorms to thrive.
Now, as the cold front actually comes through I think there will be a few isolated thunderstorms late tonight and very early tomorrow morning. But that should be about it. I'm going to continue to monitor development out to the west through the evening, but if there appears to be minimal signs of further development then our overall storm threat might even be low as well.