Flash Flood — Carroll, New Hampshire

2023-07-16 · near (8b8)wolfeboro Arpt, Carroll, New Hampshire

Event narrative

Heavy rain caused a washout on South Main Street in Wolfboro.

Wider weather episode

On the evening of July 15th isolated thunderstorms developed across southern New Hampshire. Storm movement mitigated flash flooding across the state, except for the city of Manchester where multiple storms traveled directly over the city on the evening of July 15th. Up to 2' fell in an hour over the urban city area. The intense rainfall rates lead to rapid run-off and caused localized urban street flooding with water due to run-off entering some building structures. Lighter showers passed across the area later in the evening before rain ended.

On July 16th a more widespread area of rain impacted most of the state. Rain showers began to develop around daybreak on July 16th and quickly became more widespread during the morning hours. Light to moderate rainfall became widespread across the state with embedded bands of heavy rain. Locally heavy rainfall continued straight through the morning hours into early afternoon on the 16th before rainfall intensity and coverage began to decrease. Central and Southern New Hampshire received the heaviest rainfall through the day, with less rainfall across the Connecticut River Valley and the Seacoast. Rainfall amounts of 2+' were widespread across Central New Hampshire with two corridors of locally heavier rain in this area. One corridor of heavy rain was from eastern Cheshire County through northwest Hillsborough County and into Central Merrimack County. Observed reports of 3+' of rain occurred in this region with one localized report of 4+'. The heavy rain caused isolated areas of flooded roads along with wash-outs in Antrim where a localized area of heavy rain occurred. The second corridor of heavy rain across the state was the most significant for the event. This corridor of rain ran from the Massachusetts border around Nashua all the way to the Maine border in southern Carroll County. There were numerous reports of 3+' of rain with localized areas receiving over 4' of rainfall by early afternoon. The majority of this rainfall fell in a 3 to 4 hour window in the late morning hours. The heavy rainfall rates and saturated grounds led to rapid run-off of small streams and creeks which led to flash flooding. Flash flooding was considerable in the Barnstead, Alton and Wolfeboro region where numerous roads were closed due to severe flooding and wash-outs. Additional urban flash flooding also occurred in the Manchester area due to flooded roads. Minor property flooding was also reported on numerous lakefronts across the region due to very high lake levels after this rain event.

Localized river flooding also occurred in response to the July 15-16th rainfall with river flooding beginning on July 16th and lasting through the 18th, with river crests occurring on July 17th. The Warner River touched minor flood stage with no significant impacts. The Suncook River crested at 3.53ft above flood stage on July 17th. This led to flooding of campgrounds along the river that caused the evacuation of at least one located in the floodplain. All rivers dropped below flood stage on July 18th.

In addition to the flooding, the environment supported a conditional threat for severe weather as the abundant low level moisture and strong low level jet caused significant low level shear. This caused for numerous storms to have rotation with them that triggered tornado warnings but no tornadoes were confirmed. There was however some localized tree damage with the associated thunderstorms across Southern New Hampshire.

View location on OpenStreetMap → (43.5800, -71.2700)

Source: NOAA Storm Events Database, event_id 1123769. Narrative written by the NWS forecast office that issued the report.