Region could see ice jam flooding as temperatures warm
Observer-ReporterThe Monongahela River, seen from Donora-Monessen Bridge, in a file photo
The National Weather Service in Pittsburgh has issued a flood watch in Fayette County and a hazardous weather outlook in Washington, Greene, and Fayette counties on Friday, as significant ice coverage on rivers, combined with heavy rain and warmer temperatures, pose a risk of flooding.
The flood watch and hazardous weather outlook are in effect through Saturday afternoon, according to a NWS advisory issued Thursday morning.
Up to 1.25 inches of rainfall is expected through the day on Friday, with temperatures expected to reach 54 degrees.
The rainfall on the melting snowpack “could disturb river ice, creating the potential for ice jam flooding,” the NWS advisory said.
The warming trend is expected to continue through the weekend, with temperatures fluctuating and rain increasing the likelihood of ice movement in local rivers. The rain and snow melt also will cause creeks and streams to rise.
“Rapid rises on rivers from rain, snow melt, and possible ice jams could result in localized flooding,” according to NWS.
A flood watch has been issued for the Monongahela River, which will be near flood stage on Saturday, according to the National Oceanic and Atmospheric Administration’s National Water Prediction Service.
Andrew Byrne, public affairs specialist for the U.S. Army Corps of Engineers Pittsburgh division, said none of the division’s navigation facilities on the Allegheny, Monongahela and Ohio rivers have been impacted and the facilities are fully operational.
The district operates 16 flood-control reservoirs within its 26,000-square-mile footprint to mitigate and reduce potential flood risk. The reservoirs are designed to store water during weather events and release excess storage after downstream locations have crested.
Of the 16 reservoirs the district operates, five are located in Southwestern Pennsylvania and Thursday, the reservoirs had 99.5% of their total flood-control capacity available.
Byrne said that as runoff from the winter weather continues, the reservoirs will make slow, calculated releases “to ensure the corps continues mitigating flood risk without exacerbating ice formations.”
Byrne cautioned people from going onto the ice.
“The Pittsburgh District does not encourage anyone to go on the ice. Cold water carries a number of safety hazards, and there’s no way to guarantee how thick ice will be, especially in areas with moving water, such as rivers or streams,” said Byrne. “The best way to stay safe in icy conditions is to stay off the ice.”
Residents who live near or travel through low-lying or flood-prone areas should watch for flooding and follow local weather forecasts in case a flood warning is issued, NWS said. It also recommends following its website at weather.gov/pbz/hydro; weather.gov/ohrfc or water.noaa.gov.
Ice jams form when extended periods of below-freezing temperatures cause ice to build up on the river. A sudden warm-up melts the ice quickly, breaking it into large chunks, which jam in narrow sections or bends, blocking the flow of water. The water back-up increases the risk of flooding.