Philly has its warmest January month in 91 years and just misses a snow rarity

The fact that the National Weather Service was moved to send out a social-media alert Tuesday that actual snowflakes had been sighted at Philadelphia International Airport fairly well summarized all the winter that didn’t happen around here in January 2023.

That official “trace” of snow — defined as the spotting of a solitary flake or sleet ball by the automated or human observer— reported at 2:27 p.m. was the biggest snow of a month that was the second warmest on record, with an average temperature of 43.3 degrees Fahrenheit. Based on preliminary data, that would finish behind only the incredible January of 1932.

But that January did have measurable snow, all of 0.7 inches. This one hadn’t had even a trace for the first 734½ hours. Never had a January in 139 years of recordkeeping finished with an absolute zero for snow.

Thus, when snow was recorded mixing with rain Tuesday afternoon that was in a league with a pitcher losing a perfect game on a bloop single with two outs in the ninth. Even in a warming climate and even at Philadelphia International Airport, that was quite a remarkable run, for a variety of meteorological reasons.

Winter is about to return, at least briefly, with the coldest weather since Christmas week, said Matt Brudy, meteorologist with the National Weather Service Office in Mount Holly, and wind chills in the teens and single digits during the weekend could have an extra sting given how balmy it’s been.

Philly’s official average temperature for the month was about 10 degrees above normal with daytime highs averaging just over 50. The temperature fell below freezing only three times, and failed to get above 40 only once.

Similarly, much of the East was mild and snow-deprived. New York also finished with a “trace.”

Along with a strong polar vortex circling the Arctic and keeping cold mostly confined up that way, meteorologists agree that La Niña, the anomalous cooling of waters in the equatorial Pacific, has been a big driver of the warmth. This is the third consecutive winter that has coincided with La Nina conditions.

» READ MORE: Those early winter outlooks are looking good

During La Niña, said NOAA meteorologist Allison Santorelli, the upper-level jet stream winds that move storms and that form along the boundaries of warm and cold air tend to take a more northerly track and spare the Mid-Atlantic frigid outbreaks and storms.

It is not clear what role the tropical Pacific might have played, but whatever the cause, January 1932′s record average temperature of 46.3 in Philly has never been threatened. Temperatures reached 70 or better on three consecutive days in the middle of the month in what The Inquirer called “unheard of” weather.

Olympic bobsled trials in Lake Placid, N.Y., had to be postponed because the ground was bare.

And as so often happens when the planet tries to distribute temperatures evenly, the West had a very different experience. Two inches of snow fell upon Los Angeles, and a massive snowball “riot” broke out among 500 Pasadena Junior College students, leading to multiple arrests.

Back East, the very next January, Philly recorded an average temperature of 42.6 in 1933, and 41.4 in January 1937. Both finished in the top five for all the Januaries dating to 1872.

So-called decadal variability, clusters of seasons and years characterized by extreme or benign weather, has been a challenge for climate researchers and the oceans are suspect. Long-term and ponderous changes in the Atlantic and Pacific Oceans are believed to influence the U.S. climate, says Nathaniel Johnson, a scientist with NOAA’s Geophysical Fluid Dynamics Laboratory in Princeton.

» READ MORE: Snow scarcity has a long tradition in Philly

But aside from longer-term trends, said Johnson, “a lot of the climate variability we experience is not periodic or cyclical but instead arises from chaotic weather and climate variability that we cannot predict more than a month in advance.”

He added that the study of how climate change might influence shorter-term variability is “less advanced than the changes in average climate.

» READ MORE: Philly winters can be snowy and cold even in a warming climate

“However, as global climate models become more advanced, we are making progress in addressing how climate variability may change under global warming.”

In the very short term, the cold spell that will begin settling in Wednesday, when the forecast high is a seasonable 40, is due to end Sunday. The two-week outlook has temperatures above normal into mid-February, and not a flake of snow is in the outlook.

The Punxsutawney forecast for Thursday does call for excellent conditions for groundhog shadows.