A fast-moving spring storm system is expected to bring a round of potentially severe thunderstorms to northern Illinois Thursday afternoon and evening, along with a sharp temperature drop behind a powerful cold front.

According to the National Weather Service, temperatures will surge into the 70s and even low 80s ahead of the front before falling quickly into the 40s and 50s later in the day, with even colder readings near Lake Michigan.

The main window for severe weather is expected between about 3 p.m. and 9 p.m., with the greatest threat focused near and south of Interstate 80. Storms may begin developing by mid-afternoon and continue into the evening as the cold front pushes south across the region.

The National Weather Service says conditions will be favorable for strong to severe thunderstorms, with large hail and damaging winds as the primary threats. Hail could reach 1 to 2 inches in diameter, with isolated storms capable of producing stones larger than 2 inches. Wind gusts may approach or exceed 60 mph in the strongest storms, potentially downing tree limbs and causing localized damage.

While tornado potential appears low according to the NWS, the atmosphere will be unstable enough to support intense storms. Initial development could include discrete supercells capable of producing large hail before storms merge into a line, increasing the risk of damaging winds.

Even after the cold front passes, additional thunderstorms may continue into the evening, particularly south of the Kankakee River, where a soaking rain of 1 to 2 inches is possible.

Behind the front, gusty north winds could exceed 40 mph, especially closer to Lake Michigan, adding to the blustery feel as colder air moves in.

Friday will bring a stark contrast, with highs only in the low to mid-40s, and even cooler near Lake Michigan. A gradual warming trend is expected over the weekend, with temperatures rebounding into the 70s by early next week.