White Christmas is coming, but so is freezing rain

Consider Thursday’s mild temperatures the calm before the storm.

The National Weather Service has issued a winter weather advisory for much of Western Pennsylvania with a forecast of snow and plunging temperatures.

The advisory runs from 7 p.m. through 1 p.m. Friday and calls for temperatures to drop from today’s high of 52 to 20 degrees overnight.

“As soon as the front moves through the area this afternoon, we’ll start to get the cold air rushing in and experience a pretty significant drop in the temperature starting at about 5 p.m.,” said David Shallenberger, a meteorologist for the National Weather Service in Moon.

“The rain we’re seeing now will turn to a mix of freezing rain and sleet that should last for about half an hour before switching over to all snow,” he said.

The heaviest snowfall is expected to occur between 7 p.m. and 1 a.m. in “bursts” with accumulations of 4 to 6 inches, Shallenberger said.

Starting at 3 p.m., Level 1 travel restrictions will be in effect along the entire length of Interstate 90 and along portions of Interstate 79, according to PennDOT.

The travel restrictions also will be in effect along the Parkway West from the Fort Pitt Tunnels to Interstate 79.

Level 1 restrictions prohibit tractors without trailers or those hauling unloaded trailers, passenger vehicles towing trailers, RVs, school buses, motor coaches and motorcycles.

Allegheny County Public Works Director Stephen Shanley said at least 24 salt trucks equipped with plows will begin deployment to treat roads “as soon as the snow begins to accumulate.”

He noted that roads cannot be pretreated because the material used would be washed away by the rain.

“The rapidly dropping temperatures following the rain and the possibility of blowing snow could create challenging conditions for drivers,” Shanley said. “We recommend that drivers slow down, avoid sudden stops, increase following distance and be on the lookout for slick spots, especially on bridges and ramps.”