Flash Flood in Natrona County, Wyoming

Rainfall reports for the 24 hour period including the flash flood event ranged from 1.30 to 3.47 inches. Flooding was initially reported in downtown Casper where cars where were reported as floating in flowing water. On the south side of Casper, a house was reported as shifted off of its foundation. Interstate 25 became flooded at the peak of the event, and was closed for until well after rainfall ended. Low-lying tunnels on the south side of Casper had as much as 5 feet of water in them at the height of the storm. Damage values have been updated as of Oct 2023 and are from the FEMA presidential disaster declaration, FEMA-4739-DR-WY. No injuries or fatalities were reported to the NWS.

On June 15th, roughly between 300 PM and 415 PM MDT, slow moving thunderstorms fueled by a wet air mass led to heavy rain over parts of Natrona County, including the city of Casper, WY and surrounding suburbs. Rainfall rates of 1 to 2 inches per hour were common for many locations. These high rainfall rates combined with other factors, such as wet antecedent conditions, hilly topography, and urban impermeable surfaces resulted in the flash flood event that afternoon and evening.