A pre-winter arctic front slammed Long Island on Thursday with brief white-out conditions — courtesy of frigid gusts and snow — leading to multiple roadway wrecks and urgent appeals for residents to stay inside and avoid the brunt of December’s first big chill.

“It is clear that winter has arrived, with the harsh cold and the snow that has fallen . . . this morning,” Suffolk County Executive Steve Bellone said at a news conference in Commack alongside Police Commissioner Timothy Sini.

The plunging temperatures Thursday — a 20-degree drop in less 24 hours for much of Long Island when factoring in the wind chill — are expected to continue through Friday morning’s commute with more strong gusts, forecasters said.

Things warm up Saturday, but not before snow falls for several hours, starting in the early morning, dropping an inch or two on the Island.

Rain is forecast for the remainder of Saturday, which sees highs in the upper 40s, according to forecasters with the National Weather Service in Upton. Sunday, then, brings more rain with highs in the 50s.

An overturned bus is at the scene of an accident on Sunrise Highway on the Sayville-Bohemia border on Thursday, Dec. 15, 2016. Photo Credit: James Carbone

Officials in Nassau and Suffolk said warming shelters are open and shelter services for homeless Long Islanders stuck in the cold are available.

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Drivers on Suffolk roadways faced the brunt of the arctic blast Thursday. Authorities reported more than a dozen vehicle crashes in Suffolk, including a massive snarl on the Sunrise Highway on the Sayville-Bohemia border involving a mini school bus, a jackknifed FedEx tractor trailer truck, and 27 other vehicles.

The pileup occurred during a brief midmorning snow squall and temporarily closed the westbound lanes of the Sunrise Highway into the early afternoon, Suffolk police said. No children were aboard the bus, which overturned, setting events in motion.

Only minor and non-life-threatening injuries were reported, with six people transported to local hospitals for treatment, police said.

It wasn’t so much the snow that made the conditions hazardous, said Mitch Seldin of Bayport, who witnessed the multiple crashes.

Seldin said there was barely a half-inch of snow on the ground “but the road was pure ice.”

Calls to 911 spiked Thursday from normal levels, Sini said at the news conference at a Commack Department of Public Works facility. At one point Thursday, there were 70 calls in the queue reporting accidents and hazardous conditions, Sini said.

“Icy conditions and snow are very problematic, particularly when you had white-out conditions, which we had today,” Sini said. “That obviously affects visibility and you combine it with icy roads. It’s definitely a dangerous combination.”

Suffolk police Chief of Department Stuart Cameron said on an average day there are 149 crashes in the county. By 11 a.m. Thursday, Cameron said, 175 crashes had already been reported.

Bellone urged residents in need to take advantage of a host of programs including emergency shelters and home heating assistance.

In Nassau, County Executive Edward Mangano said Thursday that nine warming centers have opened through a partnership with the Town of Oyster Bay, the Village of Rockville Centre and the Salvation Army. Mangano also said the county’s Winter Homeless Hotline — 866-WARMBED — is taking calls and providing shelter referrals and placement.

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The Town of Hempstead opened 15 warming centers Thursday that will remain open Friday.

— With Gary Dymski and Patricia Kitchen