Expect patchy fog to perhaps be locally dense at times early this morning. In some locations, the fog may be light but there could be a low hanging overcast cloud. In any case, be prepared for the chance of encountering a rapid drop in visibility. The fog is patchy and intermittent and may not last long in any one location, but it could seem really dense at times where it does exist. Allow a little extra time to reach your destination and remember to drive with your low beam headlights in fog, not your high beams.

* WHAT...For the Extreme Heat Warning, Dangerously hot conditions with heat index values up to 112 degrees expected, with locally higher values possible. For the Heat Advisory, heat index values up to around 109 degrees expected, with locally higher values possible. * WHERE...All of southeast Missouri, and neighboring portions of southwest Illinois and far western Kentucky. * WHEN...For the Extreme Heat Warning, from 11 AM this morning to 7 PM CDT this evening. For the Heat Advisory, from 7 PM this evening to 7 PM CDT Tuesday. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses. * ADDITIONAL DETAILS...This Warning and Advisory is in effect along and west of a line from Mount Vernon, Illinois, to Murray, Kentucky.