Flash Flood — Sullivan, New Hampshire

2021-07-29 to 2021-07-30 · near Acworth, Sullivan, New Hampshire

Event narrative

Acworth was the hardest hit community during the flash flooding on July 29th. Localized rainfall amounts on July 29th approached or exceeded 4.5 inches in less than six hours. Reports from FEMA and State Officials list 75% of the town's 29 roads were damaged. Multiple bridges were damaged and destroyed. Reports on damages ranged from approximately 2 to 7 million dollars. Most damage was on Crane Brook Road and Charlestown Road at Luther Hill Road. Local officials claim damage was the worst since the 2005 floods.

Wider weather episode

A developing area of lower pressure crossed the state on the night of July 29th. Abundant moisture moved into the region ahead of this area of low pressure. Rain began by late afternoon on July 29th across the Connecticut River Valley. Rain continued to quickly spread east through the late afternoon hours across all of Central and Southern New Hampshire. Moderate rain was steady with embedded areas of heavy rain that allowed rainfall rates to peak at 3 to 4' per/hour at times. The majority of the rain fell in a 3 to 4 hour window with a general 2 to 3' south of the White Mountains. A concentrated band of rainfall extended from Cheshire County across the state to Southern Carroll County where most of the flood damage occurred as localized rainfall amounts approached 5'. Another localized maximum rainfall band was located across Southern Hillsborough County as a brief but intense band traveled across this area around 10 PM EDT. The bands of rain ended from west to east with the rain clearing the state by midnight on July 30th. The heavy rain and well above normal soil saturation led to excessive run-off even after the rain ended through the night.

View location on OpenStreetMap → (43.2200, -72.3000)

Source: NOAA Storm Events Database, event_id 976090. Narrative written by the NWS forecast office that issued the report.