As prodigious amounts of lake-effect snow fell upon upstate New York — with one report of 4 feet — a very different weather drama unfolded in Philadelphia Friday.
Snow flurries from an upper-air disturbance invaded parts of the region Friday, and at midafternoon some flakes officially landed at Philadelphia International Airport, spoiling the city’s chances of setting a February record.
As of 1:58 p.m. Friday, not even a “trace” of snow had been reported officially at PHL for the entire month, and never in 137 years of snow record-keeping has February passed without at least an official flake sighting.
But then, with February down to its last hours, the automated observing system detected snow between 1:59 and 2:11 p.m., said Jonathan O’Brien, a meteorologist at the National Weather Service Forecast Office, in Mount Holly. Thus a “T” for trace was entered into the climate record for Feb. 28, 2020.
No plowing was required.
Flakes were sighted in the region on Saturday, one of the coldest days of the winter with the high topping out at 35. But since they weren’t observed officially at the airport, the tally for the day was 0.0, and the record for Feb. 29 — 1 inch, set in 1968 — survived the challenge.
In terms of snow, it would be hard to underestimate just how low the threshold is for a "T" to appear in the daily climate report, as opposed to the 0.0 that shows up for each of the first 27 days of February.
“Trace is a very loose term,” said Nicholas Carr, O’Brien’s colleague. It refers to any amount of snow under 0.1 inches, or rain under 0.01 inches.
“Theoretically, it only takes one flake seen by an observer for a trace,” said Carr.
Dave Dombek, a meteorologist with AccuWeather Inc., called Friday’s flakes "one our biggest snowstorms of the year.”
He was only half-joking.
Generally, it has been mild here, with temperatures averaging about 4 degrees above normal for the Dec. 1 to Feb. 29 meteorological winter. But the average temperature for the three-month period, 39 degrees, would be well short of the record: 43.3, set in 1932.
The outstanding feature this winter has been the lack of snow and sustained cold. The snow-deprivation of February is particularly unusual, said Dombek.
In terms of the likelihood of snow around here, “If you were to ask me to pick two consecutive weeks out of the winter, I almost without fail would say the first two weeks in February.”
Usually plenty of cold air is available at the same time that the south is warming in a hurry, and those are ripe conditions for storms to form along frontal boundaries.
The Atlantic sea-surface temperatures are cold, reducing the chances that a storm will draw in warm air from the ocean to change snow to rain. And, typically, the upper air has chilled to a degree that it favors snow. “It’s a mature atmosphere,” said Dombek.
So where is the snow? Computer models repeatedly have foreseen spells of winter, only to lose sight of them with subsequent runs.