Mild weather last week caused ice jams on the upper Allegheny River in Venango and Armstrong counties, causing minor flooding, closing roads and businesses and even inspiring a fruity vodka cocktail.
But temperatures dipped before the jams could break completely, leaving huge piles of ice on the river in places like Oil City and Parker, where many residents remain nervous about what could happen when the weather warms for good and the ice either dams in bigger piles or breaks loose all at once, either of which can result in serious flooding.
The National Weather Service said warmer weather last week formed jams that created a backflow of water, causing banks to spill over into Parker, Armstrong County -- flooding Route 268 -- and in Oil City, Venango County.
Ice jam on Allegheny River secure for now
An ice jam on the Allegheny River, while secure for now, is creating the risk of flooding. It's also proven to be a tourist attraction. (Reuters video; 2/24/2014)
Also called ice dams, the blockages occur on a frozen-over river or stream when rain and warmer temperatures cause the water level to rise, breaking thinner ice loose. That ice then piles up behind thicker ice that isn't ready to move, blocking the water's normal flow.
"The problem with ice jams is that they can remain stable for days on end, and with little or no notice, they can shift," said Lee Hendricks, meteorologist with the National Weather Service in Pittsburgh, based in Moon.
A flood warning remains in effect for the Allegheny River in Armstrong and Clarion counties until early Thursday morning, the weather service said. Temperatures Thursday night are expected to fall below zero, which could create ideal conditions for even more ice formations.
A spike in temperatures or significant rain could break up the jam, causing a sudden, and potentially messy, release of water and huge chunks of ice.
Since the Allegheny flows basically north to south, the ideal situation would be for the ice to melt first south of Parker so that area can clear out and provide a clear path for ice as it moves down from northern communities, said Parker fire Chief Rick Amsler.
Officials in Parker watched the ice in the Allegheny River 24 hours a day from Saturday to Monday.
While the water level had receded from a precipitous 21 feet to between 18 and 20 feet, "the ice jam is still there" Chief Amsler said Tuesday. If ice from where the Clarion and Allegheny rivers meet breaks loose and pushes into Parker's clusters, it "could intensify the jam."
"This year, it is a big deal," he said. "I've seen the water at this level before. That's not that uncommon. But the amount of ice -- it's overwhelming."
Crews on Saturday rescued a Parker man in his home after he awoke at 3:30 a.m. to hear trees snapping and ice smashing into his vehicle.
Riverstone Lounge, Grill and Nightclub in Parker created a mixed drink in spirit of the weather phenomenon.
"Well, when life gives you lemons, you make lemonade. Or in this case, cherry vodka, Mandarin vodka and fruit juice," said manager Tammy Johnston.
She hasn't sold that many, though, because business was slow while the main road along the river, Route 268, was closed to traffic from Saturday through Monday morning. Crews had to move ice off the road before it reopened, she said.
The lounge wasn't damaged when the river overflowed, but water seeped into the basement of two other structures.
Ms. Johnston watched the ice speed downstream Saturday and called it "awe-inspiring."
"It looked like the log jammer at Kennywood," she said.
In Oil City Friday, ice in Oil Creek started to move downstream, then stopped at a shallow area at the confluence of the Allegheny River, creating about a mile to a mile-and-a-half ice jam, said Tom Sherman, Venango County's emergency management coordinator.
Officials ordered evacuations of the entire business district along the creek in Oil City, a senior living facility and a center for troubled youth. Staff at another senior center were told to make sure seniors "had their bag ready" with medications and other essentials in case they had to leave quickly. Four or five businesses experienced minor flooding.
"I know it seems like we probably did a lot for minor flooding, but ... that stream of Oil Creek is known for one second everything looks OK, and in a matter of 20 minutes, the water level increases by feet," he said.
The return to colder weather only puts off the nervous waiting.
Molly Born: email@example.com or 412-263-1944.