When the winters changed: The 30-year warming trend

File photo: Snow covers parked cars in Center City Monday, February 15, 2016. The winter of 2016-2017 is looking like it may be a bust for snowfall totals.

A month after a ferocious daytime snowstorm shut down Philadelphia and became an issue in a mayoralty campaign, 2 feet of snow landed atop parts of Chester County.

That winter of 1986-87 was a disruptive one, but it also marked the end of a remarkable era in local weather — and what came after has been its near mirror opposite.

Despite Saturday's storms and Sunday’s cool-down, this month is poised to become the warmest February in Philadelphia records dating to 1874, with an average temperature through Friday —  when the high of 74 set a daily record —  running around 43 degrees. That is better than 7 degrees above normal.

“I’m almost going to have put on my air-conditioner,” Mike Halpert, deputy director of the government’s Climate Prediction Center outside Washington, said Friday.

 The meteorological winter of 2016-17 (that's Dec. 1 to Feb. 28)  likely will finish in the top 7 for warmth; the meteorological winter of 2015-16 was No. 3.

The warming in Philadelphia winters has outpaced worldwide temperature increases. For the 30-year period ending in 1987, the global temperature was 0.2 degrees Fahrenheit above 20th-century averages, according to the National Centers for Environmental Information. For the 30 years ending in 2016, it was about 1 degree above.

The 30 winters ending with 1987 in Philadelphia saw an average temperature of 32.7 degrees —  the coolest such period in records dating to 1874. By comparison, the average for the last 30 years was 36 degrees, the warmest such period.

It is impossible to know whether this is unprecedented because local records only go back to 1874.

But Deke Arndt, an NCEI honcho, noted that one trend is clear in recent data: Land-mass warming generally has been more robust than the globe’s.

For 2016, “over land areas where people live, it was more than 2.5 degrees warmer than the 20th-century average,” he said. “That's significant. As a thought experiment, think about turning your thermostat up 2 to 3 degrees permanently.”

“Climate change is always lurking in the background,” said the Climate Prediction Center's Halpert, perhaps causing shifting precipitation patterns, or contributing to stubbornness among upper-air patterns. This winter, generally lower-than-normal upper-air pressures, associated with coolness, have dominated the West, with higher pressures, associated with warmth, in the East.

However, in Halpert’s view, the warming “doesn’t result in the extremes. The extremes are part of natural variability.”

Tracking the weather can seem like reading Diary of a Mad Atmosphere. “There is so much randomness,” he said.

He advises that warming aside, winters aren’t going anywhere.

“There will be cold winters,” he said. “We should enjoy this one. Next year could be the complete opposite.”