Ice jam could cause flooding on Delaware

An ice jam in the Delaware River near Trenton could cause flash floods downstream when it breaks, the National Weather Service warned Wednesday.

The jam "has resulted in a few miles of near bank full conditions" north of it, the NWS said in issuing a flash flood watch. "When this ice jam breaks, there may be enough water behind [it] to cause flash flooding downstream."

After posting that watch, the weather service posted a flood warning for Bucks and Mercer Counties for waters apparently rising behind the jam.

The watch for Philadelphia and portions of Bucks, Burlington, and Mercer Counties, was to remain in effect until daybreak Thursday, but the threat might persist for the next two days, said Mitchell Gaines at the weather service office in Mount Holly.

Temperatures were forecast to crest just above freezing Thursday, rise into the 40s on Friday,and 50s on Saturday.

"Though it is not possible at this time to determine how high the water levels will rise once the ice jam breaks, there is a risk for flash flooding," the weather service said, adding that "navigation and infrastructure, such as docks, could be affected."

The jam has already caused some problems in Trenton, where the underground garage at the Statehouse was closed because of flooding, and closed a portion of River Road from Lower Makefield Township to Morrisville.

After a record snowstorm and a run of cold temperatures followed by a rapid warm-up, suddenly liberated ice jams set off major flooding along the Delaware and the Susquehanna Rivers in January 1996, leading to a presidential disaster declaration for parts of the state.

Melting snow isn't an issue this time, but frigid temperatures have locked some river and stream waters in ice.

On Tuesday, the Philadelphia region shivered through its coldest day in 20 years, one in which the mercury fell to 4 degrees with chill factors up to -20.

Though a warm-up is underway - the high Wednesday is forecast to be around 24 - effects of Tuesday's deeper freeze lingered, with broken water mains and burst house pipes posing challenges to some utilities and residents.

SEPTA and Amtrak also wrestled with overhead power line problems Wednesday. For SEPTA, that meant the suspension of service for some time Wednesday morning on the West Trenton Line. Amtrak, in the meantime, was operating on a modified schedule on the Northeast Corridor and it canceled four of six trains between New York and Harrisburg, via Philadelphia.

Amtrak said Wednesday afternoon it planned to operate on a regular schedule on Thursday.

The operator of the regional power grid, in the meantime, lifted a call for customers to conserve electricity.

Valley Forge-based PJM Interconnection said customers broke the record for peak winter electricity use twice on Tuesday from the previous peak of 136,675 megawatts set in 2007. It said electricity use peaked at 138,000 megawatts Tuesday morning and then at 141,312 megawatts in the evening.

Besides Pennsylvania and New Jersey, PJM serves 11 other states and the District of Columbia.

PJM said challenged facing the grid included increased demand for power for heat and a number of weather-related generating plant outages.

The forecast for the remainder of the weeks calls for continually rising daytime temperatures with a high of 55 predicted for Saturday.