Philly snow forecast a 'nightmare' for meteorologists, and perhaps region

History, the calendar, and astronomical reality argued against it, and computer models were behaving like so many March hares, creating what the National Weather Service called “an absolute nightmare” for forecasters.

Yet meteorologists are saying with more confidence that the region is about to experience a major snowfall, perhaps the biggest of a bizarre season, maybe even as wild as the forecast swings of the last few days.

The National Weather Service said a foot or more was possible in the immediate Philadelphia area by the time the precipitation ends Wednesday night from a pair of nor’easters expected to ripen off the mid-Atlantic coast.

 >>READ MORE: Philadelphia region braces for 4th nor’easter in three weeks: The Latest

The weather service warned that “a dangerous storm threatens heavy accumulations of wind-driven sleet and snow which may cause widespread power outages.” A winter-storm warning was in effect from 6 p.m  Tuesday until 2 a.m. Thursday.

“We just can’t shake this winter,” said Carl Erickson, a meteorologist with AccuWeather, which was calling for  6 to 12 inches in and around Philadelphia. “If everything comes together, the calendar doesn’t matter.”

Everything coming together, however, represents quite a caveat. “It’s just so difficult,” said Erickson. The weather service expressed “unusually low confidence” in its forecast.

Leaving aside the complexities of a Rube Goldberg storm scenario featuring multiple moving parts, accumulating snow would confront significant seasonal obstacles, not the least of which is the occurrence of the vernal equinox on Tuesday.

While Monday was the 15th consecutive day of below-normal temperatures, last month was one of the warmest Februaries on record. Paved surfaces have become workingmen’s hot plates, and it will be a challenge for snow to stick to them in daytime.

>> READ MORE: Top 5 March snowstorms in Philadelphia history

You might have noticed recently that if your car was parked in the sun for a few hours, it felt as if the heat had been on full blast. That’s because the sun is gaining wattage rapidly, and the days are now longer than the nights. The time between sunrise and sunset is increasing by two minutes and 38 seconds daily, the biggest daylight gain of the year, and the sun still has an effect even behind the clouds.

Historically, late March is not Philadelphia’s snow season. It was 60 years ago that 11.4 inches of heavy, wet snow landed atop Philadelphia International Airport on March 19-20 — most of it after dark and just about all of it before spring officially arrived — but after that the daily snow records for March are unimpressive.

The record for a March 21 is 4.7, set in 1932, and the totals go down from there. In fact, April has produced bigger snowstorms than late March.

It is also likely that the forecasts Tuesday and Wednesday will be works in progress. The weather service noted in the late-day discussion that four different systems were in play, all expected to converge on the coast for assorted mayhem.

A coastal low was due to form Tuesday, with a mix of rain, snow, and sleet for the region with temperatures at the surface probably above freezing. The weather service has issued a winter weather advisory for maybe 1 to 3 inches of muck.

>> READ MORE: How to prepare for a power outage

The main event would arrive Wednesday with a second, more-potent consolidated storm that could generate snowfall rates of 1 to 3 inches an hour. Snowfall at such rates could accumulate, even in daytime, but Erickson said the most problematical times would be late in the day and after dark.

Just to add a dash of adventure, the weather service said it could not rule out the possibility of some icing on Tuesday.

Spring arrives at 12:15 p.m.

Camera icon TOM GRALISH / Staff Photographer
The daffodils are blooming on one side of Cuthbert Boulevard in Haddon Township Monday, but snow from previous March storms is still piled up in a parking lot.