A rainy Thursday with above-average temperatures will become clear and a lot colder as night falls, the National Weather Service said.
Overnight, Canadian air will move into Long Island, bringing down temperatures from the mid-40s of recent days.
By Friday morning, temperatures will be in the mid-20s and 30s, the service said in its regional summary.
"Temperatures will not rebound much at all during Friday despite mostly sunny conditions as there will be a reinforcement of colder air with a gusty NW flow," the weather service said.
"The very cold airmass will remain through the first half of the upcoming weekend. Friday night lows will range from the single digits to upper teens while highs Saturday will once again reach only the upper 20s to lower 30s as high pressure moves overhead," the summary said.
A sunny Saturday is forecast with a high of 33 degrees, followed by at least a partly sunny Sunday, when the high should hit 44 degrees.
Monday's holiday will be a close twin. Tuesday, though also warm with a high of 50 degrees, likely will be ruled by rain, the weather service said.