Ice is building on Philly’s waterways as the snowpack persists and the cold intensifies

Accompanying one of the more-enduring snowpacks in the period of record, ice has continued to build in the Philadelphia region’s waterways, and all indications are that it’s going to intensify in the next three days, perhaps significantly.

With temperatures expected to fall to single digits by Saturday night and wind gusts up to 55 mph, the region is about to experience an assault from a “cold air gun,“ said Alex Sosnowski, senior meteorologist at AccuWeather Inc.

The combination, plus the below-freezing temperatures at least through Monday and the ongoing cold spell that began last month, will not only deepen the ice cover but will make it more uniform by freezing over breaks in the ice.

“You’re going to see the ice-over become more extensive,” Sosnowski said.

Earlier in the week, icing temporarily stranded a vessel on the Delaware River that was delivering much-needed salt supplies to Philly. (They did eventually get here.)

The U.S. Coast Guard was using a 175-foot-long cutter to break up ice on a portion of the river channel that runs from the mouth of the ice-covered Delaware Bay — where Cape May-Lewes Ferry service was disrupted this week — to Trenton.

As of Friday morning, the craft had been ramming ice for 45 hours since the freeze began at the end of last month, U.S. Coast Guard Petty Officer Matthew West said.

So far, however, the ice hasn’t reached crisis levels, said Ryan Mulvey, a spokesperson for the Philadelphia Regional Port Authority. For ship traffic on the river, it’s been more a matter of “road work ahead” rather than ”road closed."

“We’re open as usual,” he said. “I think the largest ships help with breaking up some of the ice flow.”

One thing is certain, meteorologists are warning: The ice factory is going to be in full production mode until Tuesday.

And, ironically, even as precipitation deficits and drought conditions persist, flooding potential is a source of concern.

A key to melting, said Sosnowski, is having a sequence of daily average temperatures above freezing, not just daytime highs above 32 degrees. Nights also have to warm up.

The prospects of that happening aren’t looking good for the next several days. Officially, Friday was the 12th consecutive day of a snowpack of at least 5 inches at Philadelphia International Airport, the seventh-longest such stretch in records dating to the winter of 1884-85.

Daily average temperatures have been below freezing every day since Jan. 23.

Highs on Saturday and Sunday, even in the city, may struggle to reach 20 degrees, with lows in single digits Sunday and Monday mornings.

A promised warmup during the workweek wasn’t looking as toasty on Friday as it was earlier in the week. Monday’s temperatures were forecast to top out in the 20s, and no daily average temperatures are forecast above freezing through Friday.

Some rain or snow also is possible Wednesday, said Nick Guzzo, a meteorologist with the National Weather Service in Mount Holly. A storm is possible next weekend, but computer models continue to disagree with each other, and themselves.

To erase the snowpack, the region could use a warm, moist air mass and rain that would produce “river rises” that would help break up the ice, the weather service says.

But not too much rain.

Some of the worst flooding on record has resulted from ice-jamming, a signature example occurring after Philadelphia’s mammoth 1996 snowstorm.

Moist air preceding a rainfall all but erased the snowpack with a historic melt. When that air came in contact with the snow, it condensed, releasing latent heat that sped up the melting.

Rain followed, and liberated ice jams led to destructive flooding along the Delaware and the Susquehanna Rivers and a presidential disaster declaration.

NOAA’s Middle Atlantic River Forecast Center is well aware of the potential and is monitoring conditions, said senior hydrologist Johnathan Kirk.

“That’s what we have to watch for,” said Sosnowski, who well remembers 1996.

“It is going to take one of the more mild-mannered thaws to avoid ice-jam flooding,” he said.

A mild thaw is possible, Sosnowski said, but “the odds are stacked against it. It’s been so cold for so long.”