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Weather service issues flood watch due to Allegheny River ice jams

| Friday, Jan. 10, 2014, 1:16 p.m.
Jason Bridge | Valley News Dispatch
Large chunks of ice form the beginning of the ice jam on the Allegheny River as seen from 16th Street in Arnold on Friday, Jan. 10, 2014.
Jason Bridge | Valley News Dispatch
Ice covers the Allegheny River just downriver of the Tarentum Bridge on Friday, Jan. 10, 2014.
Jason Bridge | Valley News Dispatch
A seagull rests on ice over the Allegheny River just upriver of the Tarentum Bridge on Friday, Jan. 10, 2014.

Warmer weather and an anticipated significant rainfall have resulted in the National Weather Service issuing a flood watch for the Allegheny River through Tuesday.

The flood watch extends from the Allegheny Lock and Dam No. 3 at Harmar north to the Clarion County line.

The watch means that residents along the river should keep an eye on the water level and be prepared to take quick action if it rises.

The watch notice states there are three ice jams in that section of river — including the one at Arnold — but all are currently stable.

The ice jam in Arnold is between 3 and 4 feet thick and a quarter-mile long, according to Dan Jones, spokesman for the Army Corps of Engineers Pittsburgh District.

Weather for the weekend calls for temperatures rising upward of 50 degrees and remaining above freezing overnight. Rainfall Saturday could be as much as three-quarters of an inch.

The weather service said the runoff could cause the jams — the others are at Brady's Bend and Parker, both in northern Armstrong County — to move and result in sudden flooding.

The Allegheny River at Arnold isn't a place where ice jams usually occur — unlike Brady's Bend.

Typically, jams form in the bends of a river because the current is slower, according to Tom Green, a meteorologist with the National Weather Service.

He's not sure why the ice formed on the river in Arnold but he noted that the drastic change in temperature might have been a major factor.

Green said the New Ken-sington/Arnold area experienced a severe drop in temperature — about 60 degrees — in a 24-hour period, from about 50 degrees early morning Monday to a low of about minus 9 by early Tuesday.

“It's not that the low temperatures are unheard of here,” Green said. “But to make that ice formation, the quick drop in temperatures and subzero weather both contributed.”

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