The National Storm Prediction Center has issued a severe weather outlook that has the Chicago area under a risk of severe storms later Wednesday afternoon into the evening hours. The greatest threat here will be across our westernmost counties under a Slight Risk (yellow-shaded area depicting a 15 % chance of severe storms within 25 miles of a given location) with the remainder of our area under a Marginal Risk (green-shaded area depicting a 5% risk of severe storms within 25 miles of a given location). An Enhanced Risk of severe storms (tan-shaded area depicting a 10% probability of tornadoes within 25 miles of a given location) exists over Iowa, northwest Illinois into southwest Wisconsin.
A center of deepening low pressure will move northeast out of Kansas into Iowa today (see map below). This combined with warm moist low-level winds gusting in excess of 40 miles per hour will be overlain by a 80 to 90 mile-per-hour jet stream aloft and an upper-air disturbance that will further destabilize the atmosphere during the peak-heating hours, generating lines of strong thunderstorms that should maintain their strength as they move east-northeast into northern Illinois, southern Wisconsin and northwest Indiana. Greatest risk with the storms in our area will be damaging winds along with large hail, although tornadoes cannot be rules out.