The high temperature will reach 90 degrees Tuesday in the metro-east with a slight chance of showers or thunderstorms in the forecast.
Though the chance of rain is only 20 percent, the most likely time for storms is between 11 a.m. and noon, according to the National Weather Service.
The chance of rain increases to 30 percent overnight when the low will drop to 72.
On Wednesday, there is a 40 percent chance of showers and thunderstorms with a high again of 90. Westerly winds will gust up to 17 mph.
Cooler weather will move in Wednesday night, when the low will drop to 61 under mostly cloudy skies.
The high on Thursday is expected to 77 degrees under mostly sunny skies. The low Thursday night will be 61 degrees.
After below average temperatures for the first four months of the year, Illinois state climatologist Jim Angel said May was the first month since October that the average temperature in Illinois was higher than average.
The mercury averaged 63.9 degrees in May, 1.2 degrees above normal.