Heavy Rain Poses for Flash Flooding Threat Overnight

You all know that famous song by Green Day, "Wake Me Up When September Ends". Now that the 6th wettest September on record is in the books, welcome to October everyone. It was a pretty warm start to the day, with most areas starting out in the low 70s. In fact, this unseasonably warm start did lead to a broken record. The official low at the Rockford International Airport was 70°. This breaks the record warmest low of 66° that was set back on September 30th, 200. Our low this morning was also 24° above the average. Summer wasn't messing around the past 24 hours. If you are a person who loves that summer-time heat, you are in luck. The warmer weather sticks around for one more day.

Most of the region so far this first of October has remained dry. In fact, we look to remain dry through the morning hours, however a spotty shower or thunderstorm is possible later today. Highs will climb into the lower 80s, so another day of temperatures between 10° and 15° above average. A very slow-moving cold front that is draped across the Midwest will have high levels of moisture ahead of it. This will bring the chance for scattered showers and thunderstorms to the Stateline by the time we reach the evening. Because of the threat for flash flooding, a Flash Flood Watch has been issued for all of our southern Wisconsin counties including Green, Rock, and Walworth county. As well as Jo-Daviess, Stephenson, Winnebago, and Boone county in northern Illinois. This watch is in effect until 10 AM tomorrow morning.

It all begins with a large ridge of high pressure that is placed over the southeast United States. This high pressure system spins clockwise. This type of moisture will continue to transport an abundance amount of moisture allowing the atmosphere to remain moisture-rich. With that said, the threat for flash flooding increases overnight. As the evening progresses, the cold front will slowly inch into far northern Illinois. The threat for heavy rain remains in place during the overnight hours as the cold front progresses through the Stateline.

Although heavy rainfall and flash flooding pose as the biggest concern for counties along the Illinois-Wisconsin border, this cold front does bring the possibility of strong to severe storms later today. The Storm Prediction Center has placed a Slight Risk (2 out of 5) for severe weather over our western counties. This threat will be pretty isolated, so not anticipating an outbreak of severe thunderstorms. The primary threat will be for gusty winds and an isolated tornado is possible.

Overall, the heaviest of rain will stay towards the north in central Wisconsin. Rain will become more widespread across the region as this cold front sinks southward overnight tonight. A few periods of showers could linger into our morning tomorrow, with some drizzle possible by the early afternoon. This cold front overnight will kick the summer-like warmth out, bringing back a cooler and much more fall-like airmass for the middle and second half of the work week. Highs for the Wednesday - Saturday time frame will feature 60s and upper 50s.