Dangerous heat and humidity will spread across the entire area today. Peak heat indices will range from 105 to 110 or slightly higher. Very warm and muggy conditions will persist tonight.

Temperatures will reach the mid and upper 90s again Wednesday, though with slightly lower afternoon humidity. Peak heat indices of 100 to 105 are expected.

A cold front will move into the area Wednesday night, which will bring slightly cooler and less humid air to the region through the end of the week. There is a chance of thunderstorms Wednesday night as the front moves in, and some storms may be strong to severe, especially across Illinois portions of the outlook area.

 

Excessive Heat Warning—Take Action! An Excessive Heat Warning is issued within 12 hours of the onset of extremely dangerous heat conditions. The general rule of thumb for this Warning is when the maximum heat index temperature is expected to be 105° or higher for at least 2 days and night time air temperatures will not drop below 75°; however, these criteria vary across the country, especially for areas not used to extreme heat conditions. If you don’t take precautions immediately when conditions are extreme, you may become seriously ill or even die.
Our weather yesterday shown above. As you can see, we had maximum temperatures of 92 to 93 with dewpoints in the lower 80s resulting in heat index values of 105 to 110.   Since the afternoon t-storms NEVER DEVELOPED, the resultant cloud cover was thin allowing for the HIGHER TEMPERATURES and HEAT INDEX VALUES.
Tuesday’s Breakdown of Temperature and Heat Index:   (Heat Index above 90 for 14 hours    Above 100 for 8 hours)
Noon:    Temp: 93   Heat Index: 100
2pm:                  95                        104
4pm:                  97                        110
6pm:                  95                        108
8pm:                  93                        101
10pm:                90                        95
Wednesday’s Breakdown of Temperature and Heat Index:   (Heat Index above 90 for 13 hours    Above 100 for 6 hours)
Noon:    Temp: 93   Heat Index: 100
2pm:                  95                        104
4pm:                  96                        106
6pm:                  94                        104
8pm:                  93                        101
10pm:                90                        95

National Weather Service

Rick DiMiao