Skip to content
News
Link copied to clipboard

Philadelphia's first fall freeze of 2010 will be late

Ordinarily, freezing temperatures on Thanksgiving weekend in Philadelphia would be about as noteworthy as indigestion. But should the thermometer fall to 32 or lower at Philadelphia International Airport on Saturday morning, as predicted, that would officially be the first freeze of the season.

Ordinarily, freezing temperatures on Thanksgiving weekend in Philadelphia would be about as noteworthy as indigestion.

But should the thermometer fall to 32 or lower at Philadelphia International Airport on Saturday morning, as predicted, that would officially be the first freeze of the season.

Some flakes fell in the area Thursday, but Gary Szatkowski, chief meteorologist at the National Weather Service in Mount Holly, said the day's low at the airport was 39 degrees about 2 p.m.

Nov. 27 would mark the longest wait for the season's first 32-degree reading since 1939, when it didn't happen until Dec. 11.

In the 1960s, on average, the first freeze occurred Oct. 25, according to an Inquirer analysis. However, the official temperature hasn't dipped to 32 during an October since 1992, by far the longest October-freeze drought in the period of record, dating to 1874.

For the first decade of the 21st century, the average first-freeze date has been Nov. 14.

"That's not surprising to me," Szatkowski said.

The local trend - along with evidence elsewhere - tracks neatly with general worldwide warming in the last two decades.

Szatkowski said it made sense that Philadelphia would be representative of global trends, given that it lies roughly midway between the arctic, where warming is robust, and the equator, where it is less impressive.

The Earth's surface temperature has increased roughly 1.3 degrees Fahrenheit over the last century, according to the National Climate Data Center.

That overarching trend probably factors into the Philadelphia warming, said Paul G. Knight, the Pennsylvania state climatologist.

But Knight and other experts stopped short of declaring Philadelphia Exhibit A in the case for anthropogenic - caused by humans - warming.

Knight, a Pennsylvania State University meteorologist, observed that all the heat-trapping, paving, and building around the airport may influence the official readings, which are taken there.

He said Philadelphia International appeared to be an "outlier" in the region. Northeast Airport made it to freezing on Nov. 2; Reading, Nov. 1; and Pottstown, Nov. 2.

Similarly, David A. Robinson, the New Jersey state climatologist, raised an urbanization caution flag in noting a trend of freezeless Octobers in Newark dating to 1997.

"We're talking more urban warming here than any broader signal," said Robinson, a professor at Rutgers University and a contributor to the U.N. report on climate change.

The siting of stations has long been a hot issue in the climate community. The Philadelphia station has moved at least five times, and from 1884 to 1940 it was downtown. But the keepers of worldwide climate databases say they have been able to screen out biased readings.

What is evident is that the late-arriving cold in Philadelphia is part of a larger trend of longer growing seasons - the periods between the last hard freezes of spring, which are occurring earlier, and the first ones of fall, which are coming later.

"People are finding that out throughout the East," said Geoffery Parker, senior scientist at the Smithsonian Institution.

In a 23-year study of 55 forest plots in the vicinity of Edgewater, Md., published earlier this year, Parker and his colleagues found a significant increase in the biomass of trees, coinciding with longer growing seasons. "It's a surprising result," he said, adding that the amount of increase actually was beyond what was expected.

Other studies have documented an earlier greening of Pennsylvania plant life since 1982, and advancing bloom dates of lilacs since 1960, according to Alyssa Rosemartin of the USA National Phenology Network.

Said Szatkowski: "I'm comfortable saying the climate is getting warmer and wetter."