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.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS GYX wrote it up.
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.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Gray, ME wrote its last area forecast discussion before the first event at Jul 17, 2:17 PM EST, 5 hours 13 minutes earlier.
Area Forecast Discussion National Weather Service Gray ME 317 PM EDT Sat Jul 17 2021 .SYNOPSIS... A warm front will approach the area tonight resulting in an enhanced area of showers and embedded thunderstorms developing over the area Tonight into Sunday. Expect scattered showers and isolated thunderstorms to continue through mid week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A band of showers continues to develop across the White Mountains, and is beginning to push into western Maine. This activity is associated with a warm front that is lifting north across the area. The parent low is over Cleveland with pressure falls showing it moving directly east into Pennsylvania. Across the warm sector, dewpoints area in the upper 60s to 70s with temperatures approaching 80 under sunny skies. Here some destabilization has already begun with showers popping up across the NYC area. Most of our area remains north of the front, and so will continue to see simply light rain or even just cloudy skies in the far north. South of Manchester NH where the sun has broken out, some convection is possible. With the high PWAT airmass will need to watch for heavy rain in any storms that do develop. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... Overnight the rain continues to fill in as the low moves east. Within the warm sector the scattered afternoon convection will merge upscale into a more stratiform MCS. Periods of heavy rain are possible across Southern New Hampshire. With total rainfall around 1.5 inches overall most areas will be able to handle this. The flash flood guidance has been slowly dropping across the south as more rain moves in and with any of these storms that are able to move repeatedly over the same area flash flooding is possible. This would be most likely in southwestern NH but will continue without a flood watch at this time as the highest threat remains right along the MA border. Tomorrow the low will continue to move east allowing the warm frontal stratiform rain to lift further northwards into Western Maine. Rain will taper off a bit late morning before restarting later in the afternoon in the form of scattered showers and the cold core of the low moves overhead. && .LONG TERM /MONDAY THROUGH SATURDAY... A rather unsettled weather pattern continues for the first few days of the long range period before at least some improvements occur. A cyclonic flow aloft resulting from a persistent trough over the northeast along with a series of shortwaves will result in a showery pattern with some embedded convection possible through much of the week. Monday and Tuesday look to have widely scattered to scattered showers, Wednesday and Friday should have more numerous showers. Thursday appears to be the driest day of the week as we will be in between short waves...one departing Wednesday Night and another arriving Friday. Finally, High pressure at the surface and ridging aloft are expected to develop for next Saturday signaling a drier weather pattern. With the exception of Tuesday, expect high temperatures to be at or below normal. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... Short Term...Band of light rain associated with a warm front is lifting northwards through the western part of the forecast area. This has some brief reductions to MVFR visibility but otherwise ceilings have been holding in VFR even with the rain. For southern NH including MHT ASH and the Merrimack valley a very moist airmass will likely drop conditions to IFR overnight. Long Term... Overall MVFR conditions outside of shower activity where area of IFR are possible. Best chance of widespread shower activity will be on Wednesday && .MARINE... Short Term... Warm front lifts north of the waters this evening as low pressure develops over PA. Low will move northeast through the waters with additional showers possible through the start of next week. Winds and waves will hold below SCA. Long Term... Wind and waves expected to remain below SCA levels. && .HYDROLOGY... Isolated threat for flash flooding across southern New Hampshire this afternoon. Upstream convective initiation has begun and is expected to grown upscale and move east. The environment has a PWAT approaching 2 inches with a deep warm cloud depth that will support heavy rain rates in excess of 1"/hr in these cells. Overall mesomodels continue to keep the focus of the convection south of the MA border but will monitor it closely. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && SYNOPSIS... NEAR TERM...Curtis SHORT TERM...Curtis LONG TERM...Lulofs AVIATION...Curtis MARINE...Curtis/Lulofs
Hazardous Weather Outlook National Weather Service Gray ME 310 PM EDT Sat Jul 17 2021 MEZ007>009-012>014-018>028-033-NHZ001>010-013-014-181915- Northern Oxford-Northern Franklin-Central Somerset-Southern Oxford- Southern Franklin-Southern Somerset-Interior York- Central Interior Cumberland-Androscoggin-Kennebec-Interior Waldo- Coastal York-Coastal Cumberland-Sagadahoc-Lincoln-Knox-Coastal Waldo- Interior Cumberland Highlands-Northern Coos-Southern Coos- Northern Grafton-Northern Carroll-Southern Grafton-Southern Carroll- Sullivan-Merrimack-Belknap-Strafford-Interior Rockingham- Coastal Rockingham- 310 PM EDT Sat Jul 17 2021 This Hazardous Weather Outlook is for Maine, south central Maine, southwest Maine, west central Maine, western Maine, central New Hampshire, northern New Hampshire and southern New Hampshire. .DAY ONE...This afternoon and tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. NHZ011-012-015-181915- Cheshire-Eastern Hillsborough-Western And Central Hillsborough- 310 PM EDT Sat Jul 17 2021 This Hazardous Weather Outlook is for New Hampshire and southern New Hampshire. .DAY ONE...This afternoon and tonight. Isolated strong thunderstorms are possible early this evening with locally heavy rain. More numerous showers and downpours are expected Tonight into Sunday. Localized flooding is possible in persistent downpours. .DAYS TWO THROUGH SEVEN...Sunday through Friday. Hazardous weather is not expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. ANZ150>154-181915- Coastal Waters from Stonington, ME to Port Clyde, ME out 25 NM- Penobscot Bay- Coastal Waters from Port Clyde, ME to Cape Elizabeth, ME out 25 NM- Casco Bay- Coastal Waters from Cape Elizabeth, ME to Merrimack River, MA out 25 NM- 310 PM EDT Sat Jul 17 2021 This Hazardous Weather Outlook is for Atlantic coastal waters. .DAY ONE...This afternoon and tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAY ME
805 PM EDT SAT JUL 17 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0800 PM HEAVY RAIN 2 SE KEENE 42.93N 72.27W
07/17/2021 M0.97 INCH CHESHIRE NH TRAINED SPOTTER
OBSERVER REPORTED 0.97 INCHES OF RAIN IN 1
HOUR AND SEVERAL INCHES OF WATER ON VALLEY
ST.
&&
TUBBSThe Boston radar (KBOX), 140 km away, was scanning. The volume nearest the first event began at 00:32 UTC.
13 flash flood, 2 flood. Local standard time, as filed.
Erosion along several local roads, primarily shoulders and pavement damage. Majority of the damage occurred in the evening.
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.
Law Enforcement reported that Main Street in Dublin near Dublin Pond was flooded with several feet of water and stalled out vehicles.
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.
Law Enforcement reported that a portion of Roxbury Street in Keene was washed out due to flash flooding.
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.
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.
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.
Media reported Old Town Road in Peterborough washed out on both sides of the road.
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.
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.
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.
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.
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.
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.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in New Hampshire in 2021Every state in 2021This day in weather historyWarnings in New Hampshire, July 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 975970, 975964, 975664, 975965, 975663, 975968, 975666, 975657, 975665, 975654, 975658, 975656, 975655, 975992, 975990.