The meteorological winter is officially half over. It might actually even start soon.
Some accumulating snow is possible Saturday, forecasters say, although the forecast has a classic Philly-on-the-thermal-fence look, with snow changing to ice and then rain, and amounts dependent on how quickly it all goes liquid.
Before that, though, high winds with gusts of up to 40- to 50-mph will whip the region Thursday.
“Something’s coming,” said Trent Davis, a meteorologist at the National Weather Service office in Mount Holly, which has posted a 100 percent chance of precipitation for Saturday, highly unusual for an event three days away.
And as of this writing, it has a decent shot at being the biggest of the season so far, given that the current No. 1 is the 0.1 inches that fell Dec. 11. Yes, that too qualifies as highly unusual.
In only 10 winters has less — as in nothing measurable — fallen through Jan. 15. As for what happened the rest of most of those winters, snow-lovers and ski operators might want to stop reading about here.
For now, the atmosphere around here is primed for something resembling January, at least briefly, said Brad Pugh, a meteorologist at the government’s Climate Prediction Center. The cold is due to arrive Friday, and the center’s 6- to 10-day outlook calls for below-normal temperatures in the East with a confidence level of five on a scale of one to five.
For the last month, Pugh said, unusual warmth has covered Philadelphia and much of the East with temperatures 8 and 9 degrees above normal. A broad upper-level area of low pressure or trough, which favors cold and storminess, has resided over the West, and its opposite — a storm- and chill-repelling ridge of high pressure — has dominated the East.
“The pattern has been hard to break,” said Nicole LoBiondo, a meteorologist with AccuWeather Inc. “At last that trough is sliding eastward.”
The East-West dichotomy isn’t unusual, Pugh said. What happens in one end of the country typically is the reverse of what goes on in the other end, and that has to do with the size of those upper-level systems. The climate center’s extended forecast calls for a trough to develop in the East in response to ridging over the West.
The impending snow or whatever is a symptom of the change. Precipitation will break out ahead of a storm system moving from the Great Lakes to New England.
It could be cold enough at the start in the Philadelphia region for an inch or two of snow to accumulate before a changeover, forecasters say, with several inches possible well to the north and west.
Temperatures Friday morning are forecast to fall into the 20s, and not make it to 35 during the day, then drop to near 20 Saturday morning. The precipitation is expected to start in the afternoon as temperatures rise into the upper 30s, and the sooner it arrives, the more snow will fall, Davis said.
Behind the storm, it might not get above freezing on Martin Luther King Jr. Day or Tuesday. But beyond next week, Pugh said, “The forecast confidence is limited.”
If the past is an indicator, and in weather that is always a dangerous assumption, the odds would favor below-normal snow the rest of the winter. In the 10 winters in which no measurable snow had fallen by the midpoint of the meteorological season — Dec. 1 through February — snow was above long-term averages only three times.
In 1966, nothing was measured officially in Philadelphia until Jan. 22, and then 14 inches fell over the next nine days. The March Blizzard of 1993 came after a snow-less start to winter, and in 2000, a snow drought ended with a surprise 3 inches on Jan. 20, followed by a bigger surprise 8.5 on Jan. 25.
The seven other winters finished with substantially below-normal snowfall, including 1972-73, the only winter in the period of record without measurable snow, and 1.9 in 1950.