When ice forms on rivers in the winter it can look beautiful, but it can also be dangerous. The National Weather Service in Pittsburgh is looking for volunteers to help keep eyes on the rivers when they freeze.
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Shannon Hefferan, a meteorologist with the National Weather Service in Pittsburgh, is a self-described ice jam enthusiast. She recently gave an online training about how volunteers can help her and other meteorologists monitor conditions that could lead to them.
Jams happen when chunks of ice clump together to block the flow of a river. The ice can act like a dam for water flowing behind it.
In the training video, Hefferan said that can be hazardous. “The water is going to pretty much lift all those ice chunks and just go out of its banks, so it can create significant flooding where communities need to be evacuated,” she said.
And she said it can happen fast.
The Pittsburgh office collaborates with a regional office in Ohio and the Army Corps of Engineers to put out daily river forecasts for the Ohio, Allegheny, Monongahela and other river basins. Precipitation like rain or snow melt goes into the forecast. But ice can interfere with gauges along the rivers.
“So the forecast sometimes doesn’t reflect what’s actually happening,” Hefferan said. “The ice is unpredictable, and that’s why we want people to tell us what’s happening.”
River ice spotters can help December through March, especially in places where ice often forms – like along the upper Allegheny River from near the Allegheny National Forest down to Armstrong County.
Ice spotting from the public is sporadic now, and Hefferan would like to build a list of volunteers to rely on so they have the information they need to make decisions. She said river ice spotters help them to keep river communities and the barge industry informed.
The weather service can issue a river ice statement when they know ice is building, or a flood watch or warning during a big thaw if people need to be evacuated or roads are closed.
Anyone can be an ice spotter. The weather service just needs really basic information from volunteers: date, time, location, and estimated thickness of the ice.
Photos from up and downstream are helpful, too.
The training goes over the types of river ice. Sheet ice forms mostly on slower-moving rivers and reservoirs, and frazil ice forms on faster-moving water and is like a slushy drink.
“It’s ice nuclei that are suspended in the water,” Hefferan said in the video. “And they can pan together, clump together…and they might get caught up in an area and just bunched together. And that’s how you can create an ice jam.”
She also goes over safety for volunteers. The number one safety rule for river ice spotting:
“Do not stand on the ice. Just don’t. Period,” Hefferan said.
Observe river ice from the shore or a bridge, and do it with a buddy, if possible.
In the training, Hefferan teaches that jams typically form when there are consistent days of very cold temperatures and when the ice reaches four inches of thickness.
The weather service would like volunteers to provide weekly reports when a cold front moves in, daily reports when ice is breaking up, or reports multiple times a day if the river is flooding. Local emergency managers should also be notified if flooding is witnessed.
Every season is different. Hefferan said one of the reasons she’s drawn to ice is its history in this region. The infamous 1936 St. Patrick’s Day Flood in Pittsburgh, which destroyed buildings Downtown and other neighborhoods – even nearby steel mills – was the result of snowmelt, rain and ice jams.
For Hefferan, the power of water and ice is fascinating, and the potential for winter flooding in river communities has always been a serious concern that many don’t realize.
“It can wipe a community away. It can wipe your house away. It’s just as impactful, like a tornado or a flash flood in the summertime.”