In July 2023, multiple rounds of heavy rainfall led to a destructive and significant flash flood event occurring in the Northeastern United States beginning from July 9 to 29, 2023. The floods were caused by slow-moving showers and thunderstorms that produced heavy rainfall and flooding over areas that were already saturated by rainfall that took place several weeks prior, especially across the Northeastern and Mid-Atlantic regions. However, the heaviest and most destructive flash flooding was concentrated around northern New England, especially Vermont and New York as widespread rain amounts of fell in the two states on July 9–11. Additionally, downtown Montpelier, Vermont was flooded, along with numerous state roads being closed as a result of it; the highest rainfall total from the event was centered in Putnam Valley, New York, with . Across the affected areas, numerous roads and bridges were washed out, and dozens of water rescues were conducted. Transportation service was impacted by the heavy rainfall and flooding, including Amtrak in New York and Vermont and Boston's MBTA subway. The flash floods caused 11 fatalities across several states at least $2.2 billion in damage. The event was known as the Great Vermont Flood of 10–11 July 2023 by the National Weather Service in Burlington, Vermont after its significant impacts in the state on the respective dates.
Meteorological history
On July 10, areas where the flooding occurred were already saturated by recent rainfall several weeks prior, and a large area of moisture traveled from the Atlantic Ocean to the Northeastern United States, likely contributed by warm waters of the Atlantic Ocean, where moisture evaporated and produced additional rainfall over New England. The storm, producing heavy rainfall, eventually slowed over the northeastern United States due to a large high pressure area over Greenland, which stalled the storm bringing high rainfall rates.
Flash flooding occurred again on July 16 following slow-moving showers and thunderstorms which developed along a cold front, which moved parallel to a deep southwesterly flow, causing the slow motion. Most unstable convective available potential energy in the 1500 j/kg range, along with moderate convective instability, maintained by the southwesterly flow, yielded re-development of the slow-moving showers and thunderstorms, and precipitable water around the 1.8-inch values also allowed the storms to produce heavy rainfall across portions of the Northeast.
On July 21, additional flash flooding occurred after a combination of a strong convergence zone and strengthening instability led to heavy rainfall-producing thunderstorms across portions of New England. Precipitable water values in the 1.5-1.7-inch range also allowed favorable conditions for very heavy thunderstorm development. The same precipitable water values, combined with an unstable moist environment, 1500 j/kg convective available potential energy (CAPE) values, and dew points in the range caused additional thunderstorm development on July 29 producing heavy rainfall, leading to flash flooding.
Preparations and impact New York
Prior to the floods, state governor Kathy Hochul urged people to be aware of the weather and road conditions.
Flooding occurred at the United States Military Academy, inundating vehicles and forcing drivers to swim out of them. Multiple water rescues, mudslides, and flooded roads prompted the town of Cornwall to issue a No Travel Advisory. Portions of U.S. Route 9W and Palisades Interstate Parkway were washed out or collapsed and closed. Portions of New York State Route 218 were totally washed away by the floods. Areas near the Hudson River and in the Hudson Valley were flooded as a rare flash flood emergency was issued. A New York City-bound Amtrak train was stopped at Poughkeepsie due to reports of the train tracks south of Poughkeepsie being washed out, cutting off access to New York City, and was reversed and rerouted back to Rhinecliff. Amtrak Service was also suspended between New York City and Albany, as well as service from New York City to Burlington, Vermont also being suspended. In Saratoga County, U.S. Route 4 and New York State Route 32 were flooded with of rainfall. Train service on Metro-North Railroad Hudson Line were stopped between Croton–Harmon and Poughkeepsie because of downed trees and damaged tracks. Due to the heavy rainfall, New York governor Kathy Hochul issued a state of emergency for Orange County, where of rain fell on Highland Falls and West Point in the eastern corner of the county. Significant flooding also occurred in Stony Point, where water rescues occurred and several homes and a park were flooded. Highland Falls also experienced significant flooding, with numerous streets in Highland Falls flooded and access to Highland Falls from Interstate 87 and U.S. Route 6 were closed due to flooding. Newburgh–Beacon Ferry Service was unavailable on July 10. CSX Tracks were compromised in 10 locations, with washed-out tracks between Selkirk and New Jersey. Roads were washed out in Carmel as well.
1,000 flights across New York airports, including LaGuardia Airport and John F. Kennedy International Airport, were cancelled, and more than 200 were delayed across those two airports. Rainfall in the Bronx forced a brief delay in an MLB game between the New York Yankees and Chicago Cubs. A 43-year-old woman drowned after bring swept away by floodwaters in Highland Falls.
Governor Hochul stated that damage would likely exceed $37 million, the threshold for a federal disaster declaration. New York United States Senator Chuck Schumer said on July 17 that the damage to West Point alone was in excess of $100 million according to the United States Army Corps of Engineers.
On July 16, additional flash floods affected the New York metropolitan area, this time focused on Long Island. Ground stops were imposed at LaGuardia Airport and John F. Kennedy International Airport. The flooding also led to a crash on New York State Route 27 late Sunday morning, injuring a police officer, with small parts of the highway closing. Heavy rain also resulted in a baseball game between the Los Angeles Dodgers and New York Mets be delayed by over 3 hours. In Islip, of rain poured down in one hour, causing flooding across roadways in and around Islip and in Suffolk County.
Vermont
On July 9, 2023, state governor Phil Scott declared a state of emergency, allowing the potential of out-of-state resources to be used for emergency responders in the state. The following day, the Weather Prediction Center issued their first ever high risk for flash flooding in the NWS Burlington coverage zone.
In Montpelier, a travel ban was initiated after floodwaters inundated roads across the downtown area; the floodwaters itself also prompted a boil water notice issued for the entire city amid warnings that the city's drinking water system could potentially be contaminated as a result. Several of the city's government buildings, including Montpelier City Hall, were flooded and some were forced to relocate. Additionally, numerous businesses and homes were destroyed after flooding left them uninhabitable and unable to operate; this included a United States Postal Service building in the city's downtown area which did not open until 15 months later. Residents in the city were also forced to evacuate low-lying areas and locations near the Winooski River, the latter of which was prompted after the river crested to flood levels. The National Weather Service also issued their first flash flood emergency not just for Vermont, but for anywhere in Northern New England. Both directions of Interstate 89 was closed after debris was strewn across the roadway by the floodwaters, and flooding also closed numerous state roads, including Vermont Route 16. Roads were flooded in Londonderry and Weston, rendering them impassable; both towns were considered the "epicenter" of the flood impacts in Vermont as evacuations were ordered for portions of both communities. Additionally, the West River at times crested to flood levels, which in turn affected both towns; the damage resulting from there overall and the state itself was described by officials as "worse than Hurricane Irene". Nearly a dozen campers in Andover were rescued by swift boat after the bridge entering and exiting out of Andover was washed out. Rainfall totals reached in Calais. On July 11, water levels at the Wrightsville Dam crested, threatening to burst the dam or necessitating to open a spillway. By evening levels receded. The flooding prompted emergency management to rescue 44 people. Two fatalities were connected to the floods: one in Barre and one on the Appalachian Trail near Stockbridge.
Thunder Road International SpeedBowl in Barre was scheduled to host the second event of the 2023 Superstar Racing Experience auto racing season on July 20, but the event was cancelled as result of the floods, with week 2 of the competition moving to Stafford Motor Speedway in Connecticut on the same day as the scheduled Thunder Road race.
Connecticut As thunderstorms developed across Litchfield County on July 9 and 10, heavy rainfall associated with the storms produced nearly in Norfolk, producing flooding in the town and across the county, and also prompting an emergency declaration to be signed as a result of the significant flooding. A portion of Connecticut Route 272 in Norfolk was washed out by floodwaters, and numerous other state routes across Connecticut were closed as a result of the flooding, including portions of U.S. Route 7 and Connecticut Routes 63 and 126. Flooding and downed trees forced road closures in Greenwich, Danbury, New Milford, New London, and Ridgefield, and several homes in Kent were evacuated because of flooding. Numerous flash flood warnings were issued for portions of Fairfield, Hartford, Middlesex, and New London counties. Flash flooding also resulted in the closures of J.A. Minetto State Park and Indian Well State Park. The heaviest rainfall occurred across northwestern parts of the state, with Norfolk receiving and falling in Warren on July 9.
Additional heavy rains fell on July 16, producing more flooding across the state which forced more road closures and damaged infrastructures. A tornado watch was issued by the National Weather Service for the entire state a day prior, which concerned the storms that would later produce the later heavy rainfall. Flooding forced Tweed New Haven Airport to shut down temporarily and closed portions of U.S. Route 44 and Connecticut Routes 17 and 167, among numerous other roadways. In Bristol, six people were rescued from their inundated vehicles, while in Waterbury, vehicles became stranded as a result of the floodwaters. A swollen Connecticut River swept away a woman who was later rescued, and caused significant damage to around of crop field along the river near Glastonbury. The Pequabuck River overflowed, damaging a Connecticut Route 229 bridge near its intersection with Route 72. In Wolcott, a bridge partially collapsed following the overflow of a pond caused by excessive rainfall. Additionally, a microburst associated with the flood-producing storms caused sporadic tree and flashing damage in Wethersfield. A jazz festival in Hartford was cancelled; the heaviest rain fell in Hartford County as well, with one location receiving . Overall, flooding and severe weather events from both days totaled $1.68 million in damage.