Long Island weather: Temperatures to fall to the 30s, middle 20s as cold weather arrives, forecasters say

Don your coats! After an unseasonably warm fall, temperatures have fallen and will continue to be low this weekend and into next week on Long Island.

The National Weather Service forecast for Islip a low of 25 overnight, with wind chill values between 20 and 25 due to westerly winds that could gust up to 25 mph.

"People are used to it being pretty warm for the last couple of months. So this several-day period of cold weather will shock people back into the fact that it's winter," said Matt Wunsch, a meteorologist with the NWS in Upton.

Sunday's forecast high in Islip is around 39, falling as low as 24 at night, and temperatures are likely to remain low throughout the week.

After an unseasonably warm fall, this week's weather is unseasonably cold — Islip's high temperature was 8 degrees below average on Saturday and 9 degrees below average overnight compared to past years.

There is little chance of snow or other precipitation over the weekend into Monday and Tuesday, according to Wunsch.

Wunsch said the colder weather is due to western winds coming in from Canada.

"We had that system a couple days ago that brought some rain for the area. Behind that ... low pressure system that moved out, we're getting these west and northwest winds that  are bringing down this colder air from Canada," he said.

The falling temperatures on Long Island come as western New York deals with up to 4 to 6 feet of snow, with snowfall rates of 2 to 4 inches per hour. Lake-effect snow happens as warm moist air from the Great Lakes — which are unseasonably warm at the moment — rises and mixes with cold dry air overhead.

On Friday, Gov. Kathy Hochul's office declared a state of emergency, which allows state agencies to mobilize resources, for Allegany, Erie, Cattaraugus, Chautauqua, Genesee, Herkimer, Jefferson, Lewis, Oswego, St. Lawrence, Wyoming and contiguous counties. It issued travel advisories for Jefferson, Lewis and portions of Erie counties, where it said "hazardous to impossible travel conditions are expected through Monday."

The New York State Thruway has banned all commercial vehicles in both directions from Exit 46 to the Pennsylvania line on I-90 until further notice. The most western part of the New York Thruway is closed to all westbound traffic west of Exit 57, which is just south of Buffalo. Beginning Friday, the New York Department of Transportation imposed an empty and tandem commercial vehicle ban on I-86 from the Pennsylvania state line to I-390 and on U.S. Route 219 from the Pennsylvania state line to I-90.