Threat of flooding depends on Allegheny River ice jams, weekend weather
Three ice jams now stretching for 20 miles on the Allegheny River have emergency officials warning of possible localized flooding this weekend anywhere along the river from Gilpin to Pittsburgh.
One of the jams, which was 3.5 miles long from Tarentum to New Kensington earlier this week had grown to five miles long by Friday, extending downstream to Springdale, said Ian McKelvey, Army Corps of Engineers supervisor of operations for the Allegheny River.
Matt Brown, Allegheny County’s chief of Emergency Services, issued a warning Friday regarding ice jams and possible flooding all along the Allegheny River this weekend.
Then there’s the Kiski River, where another miles-long ice jam caused the National Weather Service on Friday to extend a flood warning for a second time in three days.
It now remains in effect until 5 p.m. today.
The warning covers Hyde Park, Leechburg, West Leechburg and Vandergrift.
A voluntary evacuation has been in effect for several days in Gilpin’s Banfield neighborhood because of potential flooding.
According to experts, the unusual amount of ice jams — especially closer to Pittsburgh — was caused by two weeks of freaky weather that ranged from long snaps of subzero temperatures interrupted by some balmy days with highs in the mid-60s, along with snowstorms and appreciable amounts of rain.
The bulk of the Allegheny’s ice jams are north of Schenley at the confluence of the Kiski River, which is a major tributary of the Allegheny.
In fact, ice that broke free from jams farther north on the Allegheny and the Kiski caused the additional buildup of ice just downstream of the Tarentum Bridge, McKelvey said.
The Allegheny’s other ice jams stretch about eight miles from the Schenley section of Gilpin to Dam 6 in South Buffalo, then 20 more miles north to Crooked Creek just south of Ford City.
Then there’s more ice farther north on the Allegheny.
Although ice is common in the Armstrong County pools, it’s unknown how and if it that ice will continue to add to the jam closer to Pittsburgh.
“There’s a lot of ice,” said Mike Fries, meteorologist with the National Weather Service in Moon.
Another issue is that ice from the Allegheny will flow into the Ohio, perhaps adding to an already debilitating ice jam at the Emsworth dam. The Corps is watching the river closely and working at the Emsworth lock and dam.
A warm weekend forecast
Fries and McKelvey can’t say for sure how the warm weather will hasten ice jams breaking up.
“The warmer weather will melt the ice, make it weaker and susceptible to breaking up and possibly causing problems with other ice jams,” Fries said.
Because there isn’t a lot of rain in the forecast, officials are not calling for extreme flooding.
However, they cannot predict with certainty what will happen.
The weekend forecast calls for temperatures never dipping below freezing, Fries said.
Today’s high will reach the mid-40s, Sunday in the upper-40s and Monday in the mid-50s.
A half-inch of rain is forecast, too.
Allegheny County Emergency Services is working closely with the Army Corps of Engineers, the Coast Guard and the Pennsylvania Emergency Management Agency to continue monitoring the situation.