Highway maintenance supervisor Bill Murray, and workers Nick Martinez, and...

Highway maintenance supervisor Bill Murray, and workers Nick Martinez, and Larry Tillman, check trucks and equipment connections in preparation for a potential storm, at DOT operations in Melville, Tuesday, Nov. 25, 2014. Credit: Danielle Finkelstein

Not many Long Islanders will be giving thanks for a snow-bearing nor'easter that's set to disrupt holiday travel plans Wednesday.

A winter weather advisory is in effect from 7 a.m. Wednesday to 1 p.m. Thursday for northern Nassau County warning of snow, sleet or freezing rain that will "cause travel difficulties," the National Weather Service said.

"Be prepared for slippery roads and limited visibilities," with possible snow accumulation of 3 to 5 inches.

Most other parts of the Island can expect 1 to 2 inches, with less than an inch for the East End and most of Suffolk's South Shore.

"Uncertainty still exists with the track of the system, which has big impacts on where the rain/snow line sets up," the service said.

State officials advised holiday motorists to avoid the traditional travel day and leave early on Thanksgiving instead.

"The day before Thanksgiving is the busiest travel day of the year and the snowstorm in the eastern portion of the state is expected to significantly impact road conditions" Wednesday morning, state Transportation Commissioner Joan McDonald said in a news release.

Also advising holiday travelers to adjust their plans was Gov. Andrew M. Cuomo, who in a news release outlined steps the state is taking, which include: the Long Island Rail Road's activating switch heaters, and about 200 pieces of snow equipment being made available at Port Authority airports and more than 60 at bridges and tunnels.

Rain was expected to start Wednesday before sunrise, picking up in intensity and switching to a rain and snow mix from late morning to early afternoon, said David Stark, a National Weather Service meteorologist in Upton.

As temperatures drop in the afternoon, areas of western Long Island were expected to see all snow, he said, with the East End likely to remain a snow and rain mix.

Pinpointing precise timing and lines of transition is challenging, he said, but, the all-snow scenario is likely to last longer the further west you are on the Island.

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