In a three-day period on September 11, to September 13, 2023, slow-moving thunderstorms associated with a low-pressure area caused flash flooding across multiple states across the Northeastern and Mid-Atlantic regions of the United States. A stationary front, combined with a convergence zone, caused significant flooding, prompting the National Weather Service to issue multiple flash flood warnings and two flash flood emergencies, one for the city of Leominster, Massachusetts, and the other for the Baltimore, Maryland, area. Several minor injuries occurred during the severe weather event, and hundreds of homes and vehicles were flooded. Evacuations also occurred after concerns of a compromised dam near a neighborhood of Leominster, and all schools in the city were closed the day after the floods. Massachusetts governor Maura Healey declared a state of emergency for Leominster and North Attleborough following the floods.
Meteorological synopsis
On September 11, a stationary frontal boundary, combined with a low-pressure area in eastern New Jersey and a convergence zone extending across Connecticut, Rhode Island, and Massachusetts, brought slow-moving showers and thunderstorms to the Northeastern United States, bringing heavy rainfall across portions of the region. Favorable thermodynamics also supported thunderstorm development, and surface-based convective available potential energy in the 1000-1500 J/kg values were also in place across a small portion of the region. Matthew Belk, a National Weather Service meteorologist, stated that the flood was a "200-year event".
Impact
Massachusetts
Streets and numerous homes were flooded in the city of Leominster, and the downtown area there was also flooded, where buildings were flooded and a few partially collapsed. A sinkhole also opened near a Cadillac car dealership, damaging vehicles there. Massachusetts governor Maura Healey described the flooding "catastrophic", and a flash flood emergency was issued for Leominster and Fitchburg. Residential areas in neighborhoods near Leominster were asked to immediately evacuated as concerns were raised over the Barrett Park Pond Dam, which was compromised and was already in poor condition. Homes near Route 117 near Fall Brook, a neighborhood of Leominster, were "significantly damaged". School buildings near Leominster also suffered damage, and more than 15 roads, including portions of the Massachusetts Turnpike (I-90), Route 13 and Route 2, were closed due to flooding and road damage. At least of rain fell in several hours in Leominster, and an evacuation order was also issued for low-lying areas near Fall Brook and the North Nashua River. Several minor injuries also occurred, as many vehicles were submerged in floodwaters. MBTA Commuter Rail service was also affected, with trains and buses being terminated, diverted, or originating at a different station, including trains along the Fitchburg Line. Leominster mayor Dean Mazzarella stated, "Find a high spot somewhere. Find a high spot and stay there until this is over.", and also claimed that at least of rain fell. More than $40 million in damages occurred to city infastructure.
Flood damage also occurred in North Attleborough, where 200 homes were flooded, including basements, and vehicles were submerged. Several roads were closed, and the emergency operations center was activated there. Two Boston Red Sox games were postponed due to the rainfall. Nearly 2,400 power outages occurred across the state. A tornado warning was also issued for Bristol, Norfolk, and Plymouth counties after the storm which prompted the warning in Rhode Island moved into southern portions of the state.
Connecticut
On September 13, streets were flooded in West Hartford, submerging a car, as a flash flood warning was issued for Hartford. Roads were also flooded in Farmington, prompting law enforcement to place signs and barricades across the flooded area. At least eight people were rescued in Danbury as cars were submerged in floodwaters. Route 317 was closed near Roxbury, and a Holiday Inn hotel was damaged by floods. Flash flood warnings were issued for several counties in the state, and a severe thunderstorm warning was issued for the Hartford area as streets and buildings were flooded there. Flooding also occurred in Bristol, where flooded roads submerged at least three cars. One of the storms which produced heavy rainfall spawned an EF1 tornado near Danielson, and Killingly, downing trees and causing minor damage to two homes, and a tornado warning was also issued for that area.