Ice jam on Allegheny River in Armstrong County starting to break up

An almost 9-mile-long ice jam in Armstrong County is slowly breaking up between the Mosgrove and Rimer locks and dams on the Allegheny River.

Flooding is a threat in areas with tributaries north of Kittanning in the Allegheny River area, according to the U.S. Army Corps of Engineers and the National Weather Service.

But Thursday’s higher temperatures and rain could cause a slow and perhaps uneventful melt.

Some yards already are flooded in the Brady’s Bend areas, according to Shannon Hefferan, meteorologist for the National Weather Service in Moon.

Last week’s Polar vortex combined with high temperatures this week created ice, then melting ice, causing rivers to rise. The high waters Thursday closed lock 5 in Gilpin, according to Ian McKelvey, the Army Corps’ supervisory operations specialist for locks and dams.

The lock should be operational again sometime Saturday or Sunday, according to McKelvey.

But the risk of flooding is greatest in the areas where the ice is jamming further up the Allegheny, north of Kittanning to Brady’s Bend, especially tributaries, McKelvey said.

The ice, which was about a foot thick last week, is “rotting” or starting to break up, and is now about 6 to 8 inches thick, according to Hefferan.

Mary Ann Thomas is a Tribune-Review staff writer. You can contact Mary Ann at 724-226-4691, mthomas@tribweb.com or via Twitter @MaThomas_Trib.