Officials warned residents to brace for the possibility of flooding Thursday.
Lake, Porter, Newton, Jasper, Cook and Will counties are under a flood watch from 3 a.m. through Thursday afternoon.
The National Weather Service warned that heavy rain, hail and dense fog is possible throughout Thursday. Rain and melting snow also could cause flooding and create hazardous driving conditions.
The region could see a high of 54 degrees Thursday before temperatures fall to a low of 27 degrees.
Even one degree difference in air temperature could turn rain into periods of heavy snow, sleet or freezing rain, according to the National Weather Service. Meteorologists said snow and sleet are likely in northern Illinois near the Wisconsin border.
The area also could feel strong wind gusts of up to 50 mph Thursday night, according to the National Weather Service.
Indiana State Police advised motorists to slow down in rain and never drive into flowing water. If a car does end up in water, troopers said motorists should get out through a window and climb on top of the car until help arrives.
Troopers said about 6 inches of standing water will reach the bottom of most car doors and 1 foot of water will float most vehicles.