Heat Advisory

* WHAT...For the Heat Advisory, peak heat index values up to 100 to 110 degrees expected. For the Dense Fog Advisory, visibility less than one quarter mile in dense fog.

* WHERE...Boone, Kane, Kendall, and McHenry Counties.

* WHEN...For the Dense Fog Advisory, until 8 AM CDT this morning. For the Heat Advisory, until 9 PM CDT this evening.

* IMPACTS...Hot temperatures and high humidity may cause heat illnesses. Low visibility could make driving conditions hazardous.