Areas of fog have developed across the area early this morning. Some of the fog may become locally dense, with visibility of a quarter mile or less. Drivers should be prepared for rapidly changing visibility. If you encounter dense fog while driving, slow down and use low beam headlights. Leave plenty of space between you and other drivers.

* WHAT...Heat index values up to 100 degrees. * WHERE...In New Jersey, Morris and Hunterdon Counties. In Pennsylvania, Upper Bucks, Western Chester, and Western Montgomery Counties. * WHEN...Until 8 PM EDT this evening. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses. * ADDITIONAL DETAILS...Warm and very humid conditions at night will not offer much relief from the heat and humidity.