Dense fog ahead of potentially record temperatures is lowering visibility in Pennsylvania, New Jersey and Delaware for the Tuesday morning commute.
The National Weather Service issued a Dense Fog Advisory in effect until 10 a.m. for all counties in the Philadelphia region.
Forecasters say visibility of a quarter mile or less could drop to zero before it lifts in the morning.
Motorists are urged to slow down and use caution.
The Philadelphia International Airport also warned travelers of possible delays and cancellations due to fog.