Monday marked an unusual start to the meteorological winter, with a daily high for Long Island that surpassed 60 degrees, the National Weather Service said.
Most of Monday will be more than 20 degrees above the December mean temperature of 34 degrees, thanks to a short-lived warm front.
The service's Upton office forecast a daily high of 58, with a slight chance of showers after 1 p.m.
The high Monday at Long Island MacArthur Airport in Ronkonkoma was 63 at 11:23 a.m., shy of the record 67 in 2001, said David Stark, a meteorologist at Upton.
The start of the meteorological winter, which runs Dec. 1 to the end of February, marks the coldest three-month period for the northern hemisphere, according to the service.
The unseasonably mild conditions eventually will be replaced with colder air and the possibility of a wintry mix starting Tuesday night.
A stretch of incoming and outgoing frontal systems will generate sudden changes in temperature for most of the week, the service said.
As the warm front moves away, there's a greater chance of rain and cooler temperatures.
Monday night lows are expected in the mid 30s with north winds gusting up to 22 mph.
Tuesday calls for a high near 40, with east winds from 9 to 14 mph, and chance of precipitation is 30 percent.
Rain is expected after 4 p.m. East winds then kick up, with gusts as high as 25 mph. Wind chill values could make it feel more like 30 degrees, the service said, and the chance of precipitation is 80 percent.
There's some chance of a rain-snow mix Tuesday night, especially in northern Nassau County, the service said.
Another lifting warm front means any precipitation will quickly transition into "light rain or drizzle" by Wednesday morning, when daily temperatures again climb into the low to mid 50s. There also is a 20 percent to 30 percent chance of rain after 1 p.m.
A cold front should quickly follow late Wednesday afternoon or evening, the service said.
Daytime temperatures Thursday and Friday are in the mid 40s, with mostly sunny skies.
Strong high pressure in the northern plains builds eastward, and by Saturday that also translates to a wet weekend. Daily temperatures Saturday and Sunday should be in the mid to high 40s, with the chance of rain ranging between 30 percent to 50 percent, the service said.