A dense fog advisory in place for the Philadelphia region Monday morning.
The National Weather Service says the fog blanketing the area could lead to visibility of a quarter-mile or less.
The fog is expected to dissipate by late morning. The weather service's advisory runs through 10 a.m.
The fog is impacting travel on the roads and in the air. Local police departments were warning motorists to use caution in the poor-visibility conditions, while delays at Philadelphia International Airport were averaging about 45 minutes due to the weather.