The Philadelphia region is getting the season’s third dose of actual cold or a reasonable facsimile. Don’t worry, you won’t have to get used to it. Business as usual for the winter of 2019-20 should return by Sunday.
With lows forecast in the mid-teens, Philadelphia might even see its lowest temperature of the winter Saturday morning, which is not saying a whole lot.
So far this season, the official reading at Philadelphia International Airport hasn’t dropped below 19 degrees — that was on Dec. 19 — and in only five of the 146 winters in the period of record has the temperature failed to go below 15.
Yes, the winter isn’t over (oh, you disagree?), but the climatologically coldest period is, and the daily long-term “normal” temperatures have begun rising.
After cresting at 40 after midnight, temperatures Friday had fallen to freezing by lunchtime and wind wind chills were in the low 20s. They are not supposed to get past 35 Saturday, which would be something a little bit different: On only four days this winter has the temperature peaked at 35 or lower.
On just one occasion, back on that same Dec. 19, has it stayed below 32 all day; on average, Philadelphia has 13 such days. The incredibly mild winter of 1997-98 was the only one with just one of them.
By Sunday, it will be back to abnormal, with temperatures heading back toward 50, followed by several days of above-normal readings.
In other words, this will be a drive-by “migratory cold shot," just like the last two, said Paul Walker, a meteorologist with AccuWeather Inc.
Snow? Sorry, wrong winter, and the lack of it probably has contributed to the lack of cold, said David A. Robinson, the New Jersey state climatologist and keeper of the Rutgers University SnowLab. Of course, most of the time it hasn’t been cold enough to snow, and the absence of either might well be related to the other.
"You don’t know whether it’s the dog wagging the tail, or the tail wagging the dog,” said Walker. In any event, that dog likely is not a Siberian Husky.
The polar bears might be loving it. Meteorologists and the data agree that the cold has been bottled up in the Arctic, more or less trapped by an intensely swirling polar vortex.
The vortex has to weaken before the Arctic freezer can empty some of its contents deep into the United States
January was quite warm in the contiguous 48 states, and worldwide the month likely will finish among the warmest Januaries on record when the government issues its monthly update next week.
But parts of Alaska have been an icebox. And although you wouldn’t know it around here, the extent of the snow cover across North America has been amazingly close to normal, Robinson said.
In his view, however, the absence of snow locally almost certainly has something to do with the lack of cold.
Snow cover is a refrigerant, and an efficient solar-energy repellent. On clear nights with no wind and a snow cover, any daytime heating gets launched into space in a hurry and temperatures tumble.
As an example, Robinson cited Saranac Lake, N.Y., where a foot of snow was on the ground and the temperature plummeted to 26 below zero during last weekend.
So far the various computer models and the long-range forecasters are staying the course, with Punxsutawney Phil foreseeing an early spring after he was rousted from his burrow back on Feb. 2.
The government’s outlook through Feb. 26 favors continued above-normal temperatures, and on Valentine’s Day computer models are offering no virtual love for the snow-lovers or ski resorts.
Late-season snows have been known to happen; however, the sun makes its largest radiation gains of the year in February, and day lengths are increasing by about 2½ minutes daily.