Snow likely Thursday night; weekend mess near certainty
The Friday morning commute could get complicated. Another storm is likely Friday night, perhaps into Sunday, but it's unclear how much snow or ice would be involved.
After what has generally been a benign winter, the weather is about to take an eventful -- and decidedly Januarish -- turn.
The drumbeat for a weekend storm continues, but late Tuesday the computer models were suggesting something more wet than white, more wintry mess than wintry mix.
In fact, it is possible that in terms of snow, an ill-timed nuisance snow on Thursday night, which could complicate the Friday-morning commute, might end up generating more snow around Philadelphia than whatever the more-ballyhooed storm produces during the weekend.
The National Weather Service was calling for perhaps some form of frozen precipitation to arrive late Saturday, a change to rain, and then perhaps change back to snow for a while late Sunday as the storm delivers a parting arctic shot that will leave in its wake the coldest air since last winter.
“It could be almost anything at this point," Maggie Samuhel, a meteorologist with AccuWeather Inc., said Tuesday.
And, of course, everything is subject to change.
“We have a lot of model runs to go between now and then,” Samuhel said.
The National Weather Service has posted a 90 percent likelihood of precipitation for Saturday night, an extraordinarily high probability four days out.
Meanwhile, the region is expected to get a prelude snowfall Thursday night with from 1 inch to perhaps 3 inches well north and west of the city, in time to complicate the Friday morning commute.
“It’s coming at a good time to accumulate,” said Samuhel.
As for the weekend, should the storm center track near Philadelphia, or to the west, it would draw in enough warm air to change any frozen precipitation at the start to rain. AccuWeather says temperatures might make a run at 50 on Sunday morning.
What happens as the storm goes away is problematic. The north winds behind the storm could mine enough cold air to generate a round of snow. And in its Tuesday afternoon discussion, the weather service said temperatures could fall so fast later in the day that all the fallen muck could flash-freeze.
In the end, the region could experience a 40-degree drop from Sunday morning to Monday morning.
Why the seesaw?
Winds circulate counterclockwise around storm centers, so areas to the east of the center -- where Philly might find itself this weekend -- get warming winds from the south, and get whiplashed by gales from the north and northwest as the center moves away.
In the wake of the storm, the region is expected to experience its coldest outbreak of the season, with temperatures on Martin Luther King Jr. Day holding in the 20s.
Samuhel said temperatures early Monday could drop to single digits in the city, with potentially some zero readings outside Philadelphia.
The region also appears to be heading into a generally cold and eventful weather period, said Kyle Imhoff, a Pennsylvania State University researcher who is the state’s climatologist.
“We do look like we’re transitioning,” he said. Rather than a “zonal” upper-air pattern with a west-to-east flow importing air from the Pacific, the pattern is becoming more “amplified” and more favorable to stronger storms and extremes of temperature.
In its two-week outlook, the government’s Climate Prediction Center is on board, and sees a high likelihood of below-normal temperatures and above-normal precipitation.
Whatever comes Saturday and Sunday, it is unlikely to be as gentle as what occurred last weekend. The snow that began Saturday evening fell at the rate of about an inch every eight hours in Philadelphia, and the final totals were mostly about latitude.
The farther south, the higher the snow amounts as north-moving moisture ran into a cold, dry barrier to the north.
More than 10 inches was measured in Washington, and one-tenth of an inch in the Poconos. In and around Philadelphia, amounts generally were in the 1.5- to 3-inch range, with up to 5 inches in southern Delaware and lower South Jersey.
The official 1.4 inches at Philadelphia International Airport raised the seasonal total to 5.3 inches, a couple of inches below the longer-term averages through Jan. 14.