Pennsylvania's warm December shatters record

Pennsylvania had the warmest December ever recorded, beating the previous average temperature by more than four degrees.

"It's unprecedented," said Paul Head, the meteorologist who leads the National Weather Service's observation program in State College. "We basically had a typical November in December."

More than 80 temperature stations throughout Pennsylvania recorded the highs, Head said, and other states in the Mid-Atlantic are also reporting record-shattering weather.

In Hanover, the average December daily high temperature was 53 degrees, and the average low was 36.5 degrees.

For comparison, Head said the normal December high is 42.6 degrees, and the normal low is 24.2 degrees. That means December 2015 was 11.4 degrees above normal. December temperatures peaked at 69 degrees on Dec. 24, Head said.

Hanover has been collecting weather data since 1993, Head said. However, Harrisburg has been collecting data since 1888.

Harrisburg recorded an average December temperature of 45.4 degrees, said Tony Mach, meteorological technician with the National Weather Service. The previous record for December was 41.8 degrees in 1923.

While it was the warmest December, that might not be the case for the entire winter. Data shows that Pennsylvania's warmest winter on record is the winter of 1931-1932, Head said.

Head pointed out that, even if the rest of this winter has normal temperatures, the high December averages would already make 2015-2016 one of the overall warmest winters known to humanity.

"But to say that this is going to be the warmest on record before we've even gone through January would be a little premature," he added.

The warm spell might be coming to an end, said Alan Reppert, a senior meteorologist at AccuWeather.com in State College.

"It does look like we will see a shift to closer to normal temperatures here," Reppert said. "For January and February, we will still average near to above normal."

Reppert said next week will bring a "cold shot" to the Keystone State, with temperatures possibly plunging into the teens Monday night. This weekend,York County will be dry, with possible flurries Monday. Weekend temperatures will peak in the high 30s, with lows in the 20s.

Many factors contribute to warming and cooling trends. In this case, Reppert said strong winds from the Southwest has been keeping cold air from Canada out of the region.

This year, Earth experienced a strong El Nino, Head said, referring to the phenomenon of warm water temperatures in the Pacific Ocean causing global weather changes, including warmer weather throughout the Mid-Atlantic U.S.

A lower than average number of solar storms in 2015 also contributed to the warm weather, he said.

"When you have a lot of solar storms on the sun, you have a cooler sun, and the temperature on the Earth will be slightly cooler," Head said.

Though the temperature spike is drastic, Head said it's hard to predict what, if anything, that means for the rest of the year.

"If climate change is a part of this, typically when you have warmer winters, you have a cooler summer," he said.