Aug 2, 2021
Anomalously high precipitable water values worked their way into Southwestern Montana, along with weak upper level flow. This combination resulted in slow moving heavy thunderstorms, which produced some impressive rainfall totals in places. For example, a meson site reported over 1.6 of rain, with 1.36 of that falling in just 20 minutes. This lead to some urban flash flooding, with a report out of Bozeman, MT of water flowing swiftly from south to north in the downtown area.
Source: NOAA National Weather Service Storm Events Database (event 968503). Narrative written by NWS staff at the time of the event.
This event is one of many recorded floods in Gallatin County. See the full FEMA flood zone map, NFIP claim totals, and disaster history for the area.