The National Weather Service on Wednesday afternoon issued a dense fog advisory for Bergen and Passaic counties, as well as Rockland, Putnam, northern Westchester and northern Fairfield.
The advisory was in effect until 6 a.m. Thursday.
Visibility was expected to be one quarter-mile or less.
It "will make driving hazardous," the service said.
"Slow down," it added. "Use your low-beam headlights...and leave plenty of distance ahead of you in case a sudden stop is needed."
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