Extreme Heat Warning

* WHAT...Dangerously hot conditions with heat index values of 100 to 105 expected. This is the third day in a row with a forecast or observed maximum heat index over 100 degrees.

* WHERE...Southern Cook County.

* WHEN...Until 7 PM CDT this evening.

* IMPACTS...The threat for heat related illnesses increases significantly during prolonged periods of hot temperatures and high humidity levels.

* ADDITIONAL DETAILS...A cold front possibly accompanied by thunderstorms will move inland from Lake Michigan this afternoon and evening leading to rapidly improving conditions.