After a somewhat rainy and stormy Sunday afternoon and early evening, the remainder of Sunday evening should stay dry. The storms Sunday were the result of a cold front and strong jet stream winds close by, pulling in moisture from the south. A break in the rain will continue for most through about Midnight. That’s when the low level jet is expected to pick back up again bringing the return of showers and isolated thunderstorms by Monday morning.
Temperatures didn’t get quite as warm Sunday, holding in the low 70s for most; although highs reached the mid and upper 70s a little further to the south. With dew point temperatures still in the 60s Sunday night it’ll be warm and muggy with overnight lows only dropping into the mid 60s.
Low pressure to the north will pull a cold front halfway through the Stateline Monday morning, but another low over the Southern Plains will help draw the front back north and west by the afternoon. Non-severe thunderstorms are possible to start the day Monday, with a few of the stronger cores capable of producing some hail. The risk for strong to even severe storms will then gradually increase with the arrival of another low and cold front by late Monday afternoon and evening.
The Storm Prediction Center has placed the majority of the Stateline under a slight risk for severe storms, meaning if all ingredients come together there is a decent chance severe weather could occur with all hazards of severe weather are possible: damaging winds, hail and even tornadoes. The tornado risk, however, will be conditional on just how much sunshine we are able to see during the day. It’s important to note that even a little bit of sun, with the strong wind dynamics aloft, could increase the severe risk locally Monday.
It’s not unusual to get a second ‘peak’ of severe weather during the Fall season. This is because as the jet stream begins to transition from a more Summer-like pattern to a Fall one, winds within the jet stream begin to strengthen. The strengthening of the jet stream winds cause large low pressure systems to develop – like the two we have coming this week – and stronger cold fronts to move through.
The strong lows pull up unseasonably warm and humid air that then clashes with the drier and colder air behind the cold front. This second peak of severe weather often times occurs during the months of October and November.
The timeline for severe thunderstorms locally appears to be highest between 3pm and 9pm as an arcing cold front moves across west-central Illinois, and low pressure nears northwest Illinois. It’s near the low and arcing cold front we will have to watch for any individual, rotating, thunderstorms that would pose a tornado risk. By Monday night the low will be passing over southern Wisconsin, moving to the east by Tuesday morning. Make sure to remain weather aware Monday, knowing where you’ll be in the afternoon and evening and having a plan in place should severe thunderstorms occur.