Allegheny River steams while nearly frozen
Ice was flowing down the Allegheny River past Tarentum Thursday morning, when the region set a new low temperature record.
The temperature bottomed out at 5 below zero, besting the previous record of 3 below for the day that had stood since 1971, according to National Weather Service meteorologist Jason Frazier.
The frigid air and wind helped ice form on the surface of the river. It could be heard smashing against a pier of the Tarentum Bridge.
While water carried the ice down-river toward Pittsburgh, steam was seen wafting in the opposite direction, up-river.
Frazier explained the steam is the result of evaporation, and the difference between the temperature of the air and the water.
While the river water is dangerously cold, it’s warmer than the air. While he didn’t have exact numbers, Frazier said if the water is below freezing — 25, for instance — that still was 30 degrees warmer than the air over it on Thursday.
“The water doesn’t respond as quickly to changes in temperature,” Frazier said. “The water is still significantly warmer than the air temperature going on right now.”
Because it’s the product of the recent and brief cold snap, the ice isn’t very thick at all — kind of like the skin on a boat of gravy.
While ice was flowing on the Allegheny, the Monongahela was clear. Frazier said the Allegheny is more prone to ice formation because it’s further north than the Mon and gets cold temperatures for longer.
While some snow is expected overnight Thursday into Friday morning — between one and two inches by 11 a.m. Friday — the snow and the ice won’t be around much longer, as the region is going to be quickly warming up.
Temperatures are forecast to be in the 20s on Friday, and reaching the low-to-mid 50s by the end of the weekend, thanks to a push of warm air from the south, Frazier said.
Brian Rittmeyer is a Tribune-Review staff writer. You can contact Brian at 724-226-4701, [email protected] or via Twitter @BCRittmeyer.