Update 5:30 p.m.
National Weather Service forecasters say between 1 and 4 inches of snow could accumulate during the overnight hours into Friday morning.
Steady rain that has blanketed Riverhead for most of the day will let up in the evening, but snow will return to the area around 9 or 10 p.m. as the last edge of the storm begins to sweep through, said NWS meteorologist Lauren Nash.
Eastern sections of town will be hit less hard by this second round of snowfall, she said.
“Most of it is going to rotate north and west,” Ms. Nash said.
Gusts of up to 35 mph can also be expected through the overnight. By daybreak, the snow will move out of the area, Ms. Nash said.
Governor Andrew Cuomo declared a state of emergency for Long Island, New York City and the Mid-Hudson region on Thursday. Riverhead Town officials are waring motorists to be cautious on the slippery roadways.
Update 10:30 a.m.
With warmer air moving into the area, the snowfall has changed to rain across most of the North Fork, according to the National Weather Service.
“It’s going to be rain with a few sleet pellets mixed in,” said meteorologist Joe Picca. The rain will continue into the afternoon, lessening in intensity throughout the day.
During the overnight, snow may return to the area, dumping another 2 to 3 inches, Mr. Picca said.
Mattituck reported receiving 6.8 inches, while a spotter in Orient saw 6.5 inches of snow, according to the NWS. The highest amount nearby was farther west in Shoreham, where weather reports showed more than 10 inches of accumulation.
Update 9:30 a.m.
The National Weather Service is now reporting that snow is expected to change over to rain around noon to 1 p.m.
Update 4:45 a.m.
The more than an inch of snow that has accumulated with the current nor’easter has begun to mix with rain and will turn back to more snow in the overnight hours tomorrow, weather officials are saying. As much as four inches is expected to fall on the North Fork in the next 24 hours.
A Winter Storm Warning remains in effect until 6 a.m. Friday and a Coastal Flood Statement has been issued beginning at 5 p.m. Thursday.
Temperatures will hoover above freezing, getting as high as 38 degrees before dipping below freezing in the overnight hours.
An early morning blast of up to 5 inches of snow will make for a dangerous morning commute Thursday before switching over to steady rain throughout the day, weather experts said.
“It’s going to be a pretty raw, ugly day,” said National Weather Service meteorologist David Stark. “The biggest question is when that rain transition is going to come in.”
While the exact time of the switch to rain remains up in the air, forecasts show light snow will begin falling between 1 to 3 a.m. Thursday, Mr. Stark said. By 5 a.m., the storm is expected to intensify, with snowfall “moderate to heavy at times.”
The National Weather Service has issued a Winter Weather Warning from midnight through 6 a.m. Friday for the storm.
Between 9 and 11 a.m., the snow may switch to rain as warmer air moves through the area. But temperatures will only be slightly above freezing, Mr. Stark said.
Rain will continue to pour throughout the windy day, when gusts could reach up to 45 mph, he said. On Thursday night snow could return again around 9 p.m., adding another few inches to the totals.
By Friday morning, the area could see totals from 4 to 8 inches, with higher amounts to the north.