Suffolk County Police Commissioner Timothy Sini cautioned residents to beware of “dangerous road conditions” late Saturday morning as snow turned to a wintry mix then to rain on Long Island

“We want motorists to exercise caution. If you can stay off the roads, that’s the best case scenario,” Sini said in a telephone interview shortly after 10:30 a.m. “If you have to travel, drive at reduced speeds and stay alert.”

Sini warned drivers to watch out for black ice that “is very difficult to detect.”

Because the snow fell largely overnight into the early morning hours, “we don’t have a high call volume of accidents,” he said.

Still, there were about 100 accidents reported on Long Island’s roads since midnight, Sini said, a number that is not atypical for this time of year. None of the accidents reported any major injuries, he said.

All westbound lanes of Sunrise Highway at Exit 49 were closed Saturday morning due to a crash from 7:30 a.m. to 11:05 a.m. involving a jackknifed tractor trailer, Suffolk County police said.

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The tractor trailer went out of control, struck a sport utility vehicle and a slammed into a guard rail, causing the tractor trailer to jackknife at the Lakeland Avenue exit along the line between Sayville and Bohemia, a police spokeswoman said.

It occurred after more than 2 inches of snow fell on Long Island overnight.

No injuries were reported, a police spokeswoman said.

In Nassau County, westbound lanes of the Long Island Expressway at Exit 42 were reopened about 8 a.m. after authorities closed them because of a vehicle crash at the entrance to the Northern State Parkway in Jericho, Nassau County police said.

Police announced the closure shortly before 7 a.m.

A police spokesman could not provide any further details on the crash, including if anyone was seriously injured or how many vehicles were involved.

The roadway was closed so the cars could be removed from the roadway, he said.