The pattern setting up for the Friday-Monday period is one that will feature plenty of rain, thunderstorms, a chance of flooding, a chance of severe weather, and a gigantic spread in temperatures from north to south. A strong stationary front/boundary will set up across northern Illinois, northern Indiana and northern Ohio Friday and pretty much remain in place through Sunday. The result will be a significant temperature difference across the region. High temperatures in South Bend on both Friday and Saturday will stay in the 60s. If you travel an hour south to Kokomo or Lafayette, temperatures will likely be well into the 80s. If you travel north into Michigan, highs will probably struggle to get out of the 50s both afternoons.
The frontal boundary will also be the focal point for rounds of rain and thunderstorms from Friday morning through early next week. Unfortunately, Michiana will likely be in the perfect location to see a good portion of that rain and thunderstorm activity. Saturday we could even see a few stronger thunderstorms as indicated by the Storm Prediction Center's outlook. Indiana counties are in a Marginal (Low) Risk for severe weather for the potential of a few damaging wind gusts and instances of large hail.
Perhaps the biggest weather concern through the weekend will be the heavy rainfall potential across northern Indiana and southwest Lower Michigan. Where the frontal boundary sets up will dictate who sees the most rain. And it will be a matter of miles. If the boundary sets up in central Michigan, locations like Muskegon, Grand Rapids and Detroit will see the heavies train through the weekend. If the front sets up along the Indiana-Michigan border like most forecast models suggest, then Michiana will be in the zone of concern for heavy rain and potential flooding.
The Weather Prediction Center has already placed all of Michiana in a Marginal (Low) Risk for flash flooding between 8 AM Saturday and 8 AM Sunday. Parts of the region are even in the 2nd category for flash flood risk (shown in orange). That indicates a 10-20% chance of rainfall totals reaching flash flooding criteria within 25 miles of a point. Locations in that zone include La Porte, Michigan City, Niles, South Bend, Knox, Mishawaka, Plymouth, Elkhart, Goshen, Syracuse, and Edwardsburg.