Localized dense fog is expected through early Thursday morning for most of Long Island, according to the National Weather Service.
The fog advisory was extended until 1 a.m. Thursday for Nassau and Suffolk Counties, according to Matthew Tauber, a meteorologist for the service based in Upton.
But an upcoming cold front is expected to reduce the fog conditions and increase visibility early Thursday.
"By 1 a.m. most of the fog should be lifted, so visibility is improved above a quarter-mile," Tauber said. Visibility conditions of a quarter-mile or less constitute dense fog, he said.
Wednesday morning, Suffolk County police said more than a dozen motor-vehicle accidents related to dense fog.Suffolk police had advised in an email at about 6:30 a.m. Wednesday of the hazardous driving conditions and urged caution.
Skies cleared Wednesday afternoon but the fog returned Wednesday evening.
Through Friday, Tim Morrin of the National Weather Service said temperatures should be as high as the mid 40s, about 6 to 8 degrees above the daily norms.
But Friday night, a fast-moving storm system comes in, with the threat of a wintry mix, he said.
Morrin described it as an active, quick-moving storm pattern. "So quick it doesn't appear any one storm will have the chance to get going," he said. "Most of the system's energy will consolidate well over the ocean."
Friday night marks a slight chance of rain before midnight, then a chance of snow, he said. Chance of precipitation is 30 percent.
There also is a 30 percent chance of rain and snow before noon Saturday, he said.
Morrin said once the storm moves east, temperatures will remain about normal, in the mid to upper 30s, with dry conditions from Sunday into Tuesday.