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.
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Motorists are urged to slow down and use caution.
The Philadelphia International Airport also warned travelers of possible delays and cancellations due to fog.