During the evening of July 17th an area of low pressure slowly moved east along a stationary boundary that stretched from New York to Massachusetts.  The front briefly lifted northward into southern New Hampshire pulling ample moisture with precipitable water values over 2 inches, anomalously high, even for July.  Additionally, much of this region had seen 300%+ of average rainfall over the preceding few weeks. This caused soil moisture values and streamflow conditions to be well above average.  Multiple rounds of heavy rainfall produced significant flash flooding in southern New Hampshire. Reports to the weather service included totals of nearly 7 inches of rain in Jaffrey, 5 inches in Marlborough and Swanzey, and between 2 and 3 inches in Chesterfield.
Severe flooding prompted numerous local emergency operations centers to open, and washed out road infrastructure in 14 communities in the Monadnock Region. Early estimates from state and local damages verified at over $2 million from the storm.  Cheshire County alone met the entire state indicator threshold to request a declaration of disaster for New Hampshire. Communities that sustained the most damage include Jaffrey, Keene, Richmond, and Fitzwilliam.

Flood in CHESHIRE, NEW HAMPSHIRE
From 18-JUL-21 08:00:00 to 19-JUL-21 11:00:00 (EST-5)
Location: SWANZEY
Flood cause: Heavy Rain
Property damage: 120.00K
Crop damage: 0.00K
Reported by: Emergency Manager

The Ashuelot River in Southwest New Hampshire came out of banks starting on the morning of July 18th following a period of heavy rainfall. The river flooded Carlton Road and Old Richmond Rd in Swanzey. Three residents had to be water rescued. Further downstream in Winchester the flood waters inundated a solar field that was under construction causing great damage to the equipment. The Town library and VFW also flooded from the river. Forest Lake Dam was overtopped and sandbagged. Several properties along Warwick Road were flooded as backwater from the Mirey Brook, a tributary to the Ashuelot River, came out of its banks. A USGS river gage in Swanzey crested the evening of the 19th at a stage of 12.9 feet and a flow of nearly 6,000 cfs, just under the flood levels observed in October 2005. Further downstream in Hinsdale a gage crested at 8.8 feet and nearly 9,000 cfs on the morning of the 19th.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 18-JUL-21 01:00:00 to 18-JUL-21 02:35:00 (EST-5)
Location: FITZWILLIAM DEPOT
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

The town of Richmond sustained over $200,000 in verified damage. Flooding with washouts on following roads: Fish Hatchery Rd, Tully Brook Rd, Honey Hill Rd, and NH Route 32 north of four corners. No rain reports were located in Richmond, but neighboring gages reported between 4 and 6 inches of rainfall within a 12 hour period. The heaviest rain came shortly after midnight with rates over 3 inches an hour.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 20:00:00 to 17-JUL-21 21:00:00 (EST-5)
Location: DUBLIN
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law Enforcement reported that Main Street in Dublin near Dublin Pond was flooded with several feet of water and stalled out vehicles.

Flash Flood in HILLSBOROUGH, NEW HAMPSHIRE
From 18-JUL-21 00:11:00 to 18-JUL-21 02:00:00 (EST-5)
Location: EAST DEERING
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Department of Highways

The headwaters of the Piscataquog River below Everett Dam, near East Weare flooded a portion of NH Route 149 near Deering town line with undermining of pavement.

Flood in HILLSBOROUGH, NEW HAMPSHIRE
From 18-JUL-21 03:00:00 to 18-JUL-21 19:00:00 (EST-5)
Location: NOONE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Minor flooding in Peterborough from the Contoocook River. A Granite business had flooding in the yard after the river came out of banks. No damages were reported. The USGS river gage in Peterborough reached a flow of 1,290 cfs during the early morning hours of the 18th, and had receded below 1,000 cfs by early evening.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 19:45:00 to 17-JUL-21 21:00:00 (EST-5)
Location: TROY
Flood cause: Heavy Rain
Property damage: 34.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Heavy rained washed out NH Route 124 by the town garage. Maple Lane was completely washed out and needed a temporary bridge due to approximately 25 residents being stranded. The first round of rainfall came around 8 PM EDT dropping close to 3 inches. This was followed by a second round of heavy rain shortly before midnight. The area recorded 5.5 over a 12 hour period.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 20:00:00 to 17-JUL-21 21:30:00 (EST-5)
Location: FITZWILLIAM DEPOT
Flood cause: Heavy Rain
Property damage: 235.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Significant damage with multiple road washouts. Scott Pond Road was completely washed away where the causeway crossed over a pond.  This road damage caused 12 homes to be isolated.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 23:25:00 to 18-JUL-21 02:00:00 (EST-5)
Location: KEENE
Flood cause: Heavy Rain
Property damage: 300.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Two rounds of heavy rain impacted Keene on the evening of the 17th. The first round came around 9 PM causing some localized flash flooding. Shortly after midnight another round of heavy rainfall moved over the area resulting in another surge of floodwaters into the city. In all, over 80 residential basements flooded along with several businesses. A large sinkhole developed on Roxbury Street with severe damage. There were at least 2 evacuations, one on Wetmore Street and another at Boston Place.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 20:17:00 to 17-JUL-21 21:30:00 (EST-5)
Location: KEENE
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law Enforcement reported that a portion of Roxbury Street in Keene was washed out due to flash flooding.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 23:32:00 to 18-JUL-21 02:00:00 (EST-5)
Location: FITZWILLIAM
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Multiple roads washed out. Scott Pond Road, Warren Hill Rd, Royalston Rd, Sandy Hollow Rd, Rhododendron Rd, Old Coach Road, Lower Templeton Tpke.  Nearby rain gages reported between 4 to 6 inches of rainfall, with the heaviest rain shortly after midnight.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 19:30:00 to 17-JUL-21 21:00:00 (EST-5)
Location: SWANZEY
Flood cause: Heavy Rain
Property damage: 107.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Erosion along several local roads, primarily shoulders and pavement damage. Majority of the damage occurred in the evening.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 23:45:00 to 18-JUL-21 02:00:00 (EST-5)
Location: (AFN)JAFFREY ARPT
Flood cause: Heavy Rain
Property damage: 617.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Jaffrey airport reported 6.9 in 18 hours, measuring 6 to 8 inches of rain in 24 hours. More than 15 roads were washed out, one of which lost a major culvert. Damage figures were estimated over $1 million mainly for damage to roads and bridges.  There was a voluntary evacuation for 39 homes on Letourneau Drive off Nutting Road after a bridge was flooded by a small stream.

Flash Flood in HILLSBOROUGH, NEW HAMPSHIRE
From 17-JUL-21 23:40:00 to 18-JUL-21 00:00:00 (EST-5)
Location: PETERBOROUGH
Flood cause: Heavy Rain
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Public

Media reported Old Town Road in Peterborough washed out on both sides of the road.

Flash Flood in CHESHIRE, NEW HAMPSHIRE
From 17-JUL-21 21:30:00 to 17-JUL-21 22:45:00 (EST-5)
Location: TROY
Flood cause: Heavy Rain
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Multiple roads washed out including South Street, Quarry Rd, West Hill Rd, Prospect Rd, and Brook Rd. Perkins Pond dam was overtopping near Monadnock St and Sand Dam.

Flash Flood in HILLSBOROUGH, NEW HAMPSHIRE
From 18-JUL-21 00:00:00 to 18-JUL-21 02:00:00 (EST-5)
Location: WEST PETERBOROUGH
Flood cause: Heavy Rain
Property damage: 1.00M
Crop damage: 0.00K
Reported by: Emergency Manager

Approximately $1 Million in road damages reported town wide in Peterborogh. Old Town Farm Rd and Old Jaffrey Rd received significant damage.  Old Town Farm Road is a dead end and had 18 homes isolated by the road washouts.