Wednesday and Thursday are shaping up to be wild weather days across the Chicago area, with an unknown combination of rain, ice and snow potentially causing serious travel issues and flooding.
The National Weather Service has issued a winter storm watch for DeKalb, Kane, DuPage, Cook, LaSalle, Kendall, Grundy, Will and Kankakee counties in Illinois, along with Lake, Porter, LaPorte, Newton and Jasper counties in Indiana, from Wednesday night through Thursday evening.
According to the watch, portions of northeast Illinois and northwest Indiana will see rain beginning Wednesday, which will then transition to freezing rain and sleet late Wednesday and into early Thursday, before finally turning to snow for most of the day Thursday.
Heavy snowfall rates are possible, and travel conditions will be impacted by winds that could gust as high as 40 miles per hour in some locations.
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What is unknown at this point is when exactly the transition to wintry precipitation will start, and what kind of snowfall accumulations are possible with the storm.
Wednesday is set to start out with above-average temperatures, with highs expected to climb into the 50s across the area.
Strong winds are also expected to cause some issues, but that is merely the tip of the iceberg, according to forecast models.
Those models indicate that rain will begin to fall across the area Wednesday afternoon and into the evening, causing serious flooding concerns in low-lying areas and along rivers and streams. That rain, along with the warm temperatures, could cause ice jams to break up, leading to even more flooding concerns in the coming days.
A flash flood watch is in effect for Newton and Jasper counties in Indiana, according to the National Weather Service, but forecasters say that heavy rain is expected in many areas, especially south of Interstate 80.
That rain could continue to fall through Thursday morning, but it all depends on how quickly temperatures begin to drop. The high temperature for the day will be recorded at midnight, and readings will continue to drop throughout the day, turning the precipitation into ice and then into snow by the time the system finally moves out of the area late Thursday.
Freezing rain and sleet are possible during the Thursday morning commute, with forecasters warning residents to practice safe driving habits in the event of nasty early-morning weather.
The latter part of the storm is where the biggest uncertainty still remains. The system is expected to move rapidly into the area from the Great Plains on Wednesday, but the track that it is going to take will ultimately determine how quickly the precipitation changes from rain to snow, and then how much snow could potentially fall in parts of the Chicago area.
If the storm takes a more northerly route, then the city and most of the suburbs could see accumulating snow on Thursday. While it is unclear just how much snow could fall, moisture off of Lake Michigan could potentially lead to lake-enhancement, driving up totals in the city and in the northern and western suburbs.
In the other scenario, the storm could veer more to the south, primarily impacting central Illinois and Indiana. The far southern suburbs in Kankakee County, along with parts of northwest Indiana, could also be impacted by this storm, which could drop plenty of rain and snow on the region before moving out.
Regardless of which direction the storm system moves, it remains likely that the Chicago area will see at least some snow on Thursday, with icy and windy conditions leading to serious travel concerns throughout the day.
One final threat could also emerge in the form of significant lakeshore flooding in both Illinois and northwest Indiana. Strong northerly winds are expected on Wednesday and Thursday, which could cause massive waves and pose a threat to low-lying areas near the water.
By Friday, conditions will have cleared up, with below-freezing temperatures expected to kick off the weekend. On Sunday highs are expected to rise back into the 40s, but more rain is expected to arrive in the area by Monday.