Western Pennsylvania temperatures on Friday morning could break the record for the coldest temperature ever recorded on Dec. 5 at the National Weather Service in Moon.

David Shallenberger, meteorologist at the NWS, said the temperature to beat is 12 degrees, which was set on Dec. 5, 1976.

The forecast right now shows a low of 11 degrees, hitting at around 4 a.m. Friday, he said.

The National Weather Service began documenting records in Moon when it moved from Downtown Pittsburgh around 1950, so the Dec. 5 record has been tracked since then.

“Tomorrow morning was an outlier warm day out of the trends of the year. All of the records are into the single digits or sub-zero,” Shallenberger said of the rest of December.

The temperature will begin to drop steadily just after 7 p.m. Thursday night, when it will be around 19 degrees, he said.

From there, the numbers will descend until 4 a.m., when it’s expected to break the record at 11 degrees.

The cause? A cold front, Shallenberger said.

“We just had a cold front go through today, so usually you start to see the coldest part of the air 24 hours after it passes,” he said.

Shallenberger said to be on the lookout for ice.

“Bundle up and look for those slick spots on the roads,” he said.

However, by 9-10 a.m. Friday, the temperature will already be back up to 20 degrees, according to Shallenberger.

“The high tomorrow is 33, so it’ll keep on warming up,” he said.

Similarly cold days could arrive early next week, but with a low of 20 degrees on Monday, it’s not close to Friday’s presumed record low, according to Shallenberger. The high will be 27 degrees on Monday.

“That’s going to be somewhat of a chilly day,” he said.

Tuesday’s low is set to 14 degrees, Shallenberger said, with temperatures expected to warm up into the low 30s.

As for snow, he said there’s supposed to be some on Friday, but it will hit south of the Pittsburgh region.

“We’re not going to see any accumulation,” Shallenberger said. “Maybe a few flakes, but that’s it.”

The first big snowfall of the season hit Western Pennsylvania on Tuesday morning, coating the ground and roadways and closing or delaying schools.

As anywhere from 2- to 5-inch snow totals were being reported around the region, TribLive previously reported.

Polar vortex

Meteorologists across the United States have recently been discussing a shifting polar vortex that will send multiple rounds of Arctic air into the central and eastern parts of the country through the first half of December.

This will trigger snow flurries and squalls in some areas and could fuel storms with more widespread snow as well, Accuweather reported.

Shallenberger described a polar vortex as a top that’s spinning in the north.

“Sometimes, the circulation becomes a little unstable, and you have a chunk of cold air come down from Canada,” he said.

Polar vortices aren’t unusual, according to Shallenberger, as they happen multiple times per year.

Since Friday’s incoming cold temperatures aren’t part of a “large period of cold air,” the polar vortex isn’t the cause of the predicted record-setting 11-degree temperature.

“It can impact our area, but it’s just something that can be monitored,” Shallenberger said of the polar vortices.

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