As a winter storm unfolds, Chicagoans can expect a mix of heavy rain, sleet and snow in coming days, likely causing travel concerns and flooding.
The National Weather Service issued a winter storm warning early Thursday morning into the evening for the following Illinois counties: La Salle, Kendall, Grundy, Kankakee, Livingston, parts of Cook, parts of Will. The warning was also issued for Lake and Porter counties in Indiana.
The warning will be in effect from 3 a.m. to 9 p.m. Thursday.
According to the warning, a time period of accumulating freezing rain and sleet is expected late Wednesday night into Thursday morning. By Thursday afternoon, the rain and sleet will likely turn into heavy snowfall, which could accumulate from 1 to 8 inches.
Chicagoans can expect more than 1 inch of snowfall per hour at times Thursday afternoon, officials said, accompanied by wind gusts up to 40 mph.
A winter storm watch was also issued 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.
In DuPage, La Salle, Kendall, Grundy, Kankakee, Livingston, parts of Cook and parts of Will counties in Illinois, as well as Lake, Porter, Newton and Jasper counties in Indiana, a wind advisory is in effect from 9 a.m. to 6 p.m. Wednesday.
At times, wind gusts could reach 40 to 50 mph, according to the advisory. Weather officials warned small tree limbs could be blown down and power outages are expected.
Wednesday is set to start out with above-average temperatures, with highs expected to climb into the mid 40s to low 50s across the area.
Those models indicate that rain will begin to fall across the area Wednesday afternoon and into the evening, causing 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 could depend 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 harsh 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 likely have cleared up, with below-freezing temperatures expected to kick off the weekend.