Updated Apr 12, 2024 - Science

Pittsburgh streets flooded as severe storms threaten Ohio Valley, Mid-Atlantic

Pittsburgh rescue crews take a dinghy out into the street to save a woman trapped in a car sinking in rising waters on Route 51. Swiftwater Rescue Paramedics accessed the patient and loaded her into the boat, taking her to safety at a nearby business.

Rescue crews rush to the aid of a woman who was trapped in a car sinking in rising waters on Pennsylvania Route 51 in Pittsburgh, per a Thursday night Pittsburgh Public Safety post. Officials said she wasn't injured. Photo: Pittsburgh Public Safety/Facebook

Heavy, relentless rains flooded Pittsburgh-area streets and prompted water rescues Thursday night, as a severe storm system threatened parts of the eastern U.S. into Friday.

The big picture: A rare flash flood emergency, the National Weather Service's highest flood alert category, was issued for parts of Pittsburgh, where up to 4 inches of rain had fallen just before 9:30pm Thursday.

  • The heavy rains were triggered by the same storm system that unleashed tornadoes and heavy rains across much of the South and Southeast this week, with flood emergencies declared in three other locations.

State of play: The National Weather Service received over 200 reports of severe weather from Tuesday night to Thursday evening — with reports of at least 14 tornadoes striking Texas, Florida, Louisiana, Mississippi and Alabama.

  • On Wednesday, thunderstorms brought so much rain to New Orleans that the day ranked as the third-wettest April day on record there.
  • The storm was blamed for at least two deaths.
  • By Thursday night, the storm had shattered daily rainfall records in the Pittsburgh area and prompted water rescues and road closures across Allegheny County, Pennsylvania.
  • Officials in the Allegheny County borough of Etna issued an evacuation notification late Thursday for communities in flood zones or areas prone to flooding after a local creek reached 14 feet.

Threat level: On Friday, the NWS warned of a level 2 out of four on their storm risk scale, for a "slight" risk of excessive rainfall in the in northern New England, with Maine at particular threat "due to the combination of rainfall and recent snowmelt."

  • Flood watches were in effect in northern New Hampshire and central Maine due to the threat of flash and river flooding.

Between the lines: Climate change is causing extreme precipitation events to be more intense and frequent.

  • A warmer atmosphere can hold more water vapor, which provides added moisture and energy for storm systems to wring out as heavy rainfall.

Zoom in: Widespread shower and thunderstorm activity was expected to continue Friday morning across the lower Great Lakes, Ohio Valley, Appalachians, Mid-Atlantic and the Northeast as a low pressure area intensifies and moves from the Great Lakes into Canada.

  • Severe thunderstorms, "scattered damaging winds, and isolated severe hail," are possible, the NWS said.
  • The severe threat is expected to diminish by afternoon, however.

The bottom line: This large, deepening low pressure system will be the "driving force behind active weather throughout the eastern United States until early this weekend," the NWS noted.

Go deeper: Where homes will face the most flood risk in next 30 years

Editor's note: This article has been updated with new details throughout.

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