Single-digit temperatures are expected in Philly, after biggest snow of the season

Some Alaskans evidently left their freezer doors open.

Whatever the explanation, Philadelphians and much of the nation are experiencing one pervasive and impressive cold spell.

One measure of the power and coverage of the Arctic air mass that could drive temperatures to near zero in the Philly region this week, is the fact that a winter storm warning was in effect Tuesday and Wednesday for New Orleans and the Gulf Coast.

“It may end up being a historic winter storm for some of those areas,” said Marc Chenard, senior forecaster at NOAA’s Weather Prediction Center.

Meanwhile, temperatures in Anchorage, Alaska, were averaging almost 11 degrees above normal in January through Sunday, when it got all the way to 35 degrees.

Philadelphia is unlikely to see 35 until the weekend, and on Monday, Pennsylvania, New Jersey, and Delaware were among more than 35 states from the Rockies to the Atlantic Coast that were under a weather service “cold weather advisory.”

Lows even in the city are forecast to fall into the single digits the next three mornings, with below-zero wind chills Tuesday and Wednesday, the National Weather Service says. Highs might not reach 20 on those days. The Philadelphia School District will operate on a two-hour delay Tuesday, as will Archdiocesan elementary schools in the city.

» READ MORE: Philly schools will have a delayed opening on Tuesday

Expect several days of so-called black ice, as the daytime melt refreezes on paved surfaces, something that was evident late Monday afternoon. Melting occurs at temperatures well below freezing: The late-January sun is more powerful than probably most people realize.

It’s not “impossible” that temperatures at Philadelphia International Airport make a run at hitting zero for the first time in 31 years, said Alex Staarmann, meteorologist at the weather service Mount Holly office. However, that is a long shot.

The likelihood of that happening would have been higher had five or six inches of refrigerating snow landed Sunday, he said, but the official total was two inches, and that was all but certain to flatten to an inch or less rather quickly with winds eroding the snow cover.

That said, snow is generously layered across much of the region. The weather service reported totals of three to six inches in the city’s neighboring counties to the north and west; two to three inches in the city, northern Delaware, and nearby South Jersey; and less to the south and east.

Especially at night, the snow is going to have a chilling effect on what already is an air mass plenty cold in its own right. With clear skies and light winds, any daytime warmth captured by snow escapes rapidly into space after sunset.

Staarmann said the best chance for a goose-egg at PHL would be early Thursday, when conditions may be ideal. Winds will be frisky Tuesday morning, and cloud cover is expected early Wednesday as the Gulf storm slides off the Atlantic coast.

Nothing is imminent.

That Gulf Coast storm may stay so far south that it spares even Atlanta, said Dave Dombek, senior meteorologist at AccuWeather Inc., as the cold, dry air suppresses the storm track.

Temperatures are due to moderate on the weekend, climbing well into the 30s by Saturday and perhaps reaching 40 on Sunday, close to normal. However another system may affect the region with rain or snow late in the weekend, Dombek said.

Then, computer models favor another cold shot at the end of the month, he said.

In the short term, expect temperatures the next three days to average 15 to 20 degrees below normals with icing increasing on area streams.

“It’s been awhile since we’ve seen so much ice on the area’s waterways,” said Sarah Johnson, the weather service warning coordination meteorologist in Mount Holly, adding that the Rancocas Creek in South Jersey was ice-covered. Ice also has developed on the Schuylkill.

Ice-jamming can create natural dams and exacerbate flooding during rainstorms when the weather has turned milder.

Although icing isn’t an immediate threat, it is possible that the cold spell this week could increase ice buildup, said Elena MacFarlande, hydrologist with the weather service’s Middle Atlantic Forecast Center, in State College, and bears watching.

Fortunately, said Dombek, no dramatic thawing is expected within the next 10 days, although the European forecast model was “hinting” at a significant warmup in early February, circa Groundhog Day.

Sunday’s high up that way wasn’t close to a daily record. That distinction belongs to Jan. 20, 1961, when it reached 50 degrees.

As so often happens when the cold empties out of Alaska, it slides this way. On that date, Philadelphians awoke to more than a foot of snow in the heart of one of the coldest and snowiest winters on record.