Looking Back at Connecticut's Devastating Flash Flood One Year Later

During the mid-morning hours of Sunday, August 18th, 2024, a flash flood warning was issued for the southwest corner of Connecticut. By the mid-afternoon hours, Fairfield county would be placed under a flash flood emergency after over a half foot of rain fell from a stationary thunderstorm. By that evening, a small portion of Connecticut would receive 6-12 inches of rain, resulting in a devastating flooding event that would claim three lives.

This came as a surprise to many, meteorologists included, as a flood watch was not issued over Connecticut, but instead just to the west, over eastern New York and portions of New Jersey. This is where the bulk of flooding was expected to occur that evening. There were signals from guidance depicting up to five inches of rain in southwest Connecticut, but this signal was dropped in following model runs on the morning of August 18th. The following will be looking into the impact, recovery and meteorology behind this storm.

Below: Estimated rainfall amounts from the evening of August 18th, 2024:

One of several towns at the epicenter of this flooding event was Southbury. The town was one of the first to report major flooding issues that Sunday afternoon and it was the community that really showed the true magnitude of what was transpiring in the area. After hours of training thunderstorms moved over the area, the flood waters seemed to rise within minutes. Some of the very first images of this flooding came out of the intersection in front of the Southbury Plaza, where many vehicles became stranded. Local citizens helped perform multiple rescues of people trapped within their cars before rescue officials arrived.

The town stated that up to 60 roads were affected by flooding, including a dozen total closures. 24 hours later, nine roads in the town remained completely closed. The Southbury Public Library was closed until further notice after sustaining significant damages. All parks, athletic fields and the town pool are also closed. Many parts of the town were left with a thick layer of mud after floodwaters receded.

Below: Floodwaters outside of the Southbury Plaza. Photo by NBC Connecticut:

Long after the rain stopped, the center of Southbury was flooded again early Monday morning when a logjam broke apart, allowing backed up flood waters to spill through the town once again. The fire department had to reactivate the swift water rescue team when this happened as well as abandon recovery efforts that had barely begun. This secondary flood caused much devastation to the town, possibly even more than the initial flash flood that afternoon. Pretty much the entire town was affected in one way or another by the storm.

The town's library sustained significant damage, including the loss of around 40,000 items in the basement as well as critical structural components. A temporary library had been set up at a local hotel. The library will officially re-open on September 2nd, 2025, up to two months ahead of schedule.

Below: Southbury Library shortly after the floods:

Another town that could be considered the epicenter of this flood is Oxford. Two of this storm's three fatalities occurred in the town when two women were swept away by the Little River on Route 67 after exiting their vehicle in an attempt to flee the floods after the river rose within minutes. The town sustained some of the worst damages in the state. Like Southbury, many roads were washed out and heavily damaged. After the floods, simple trips became a maze of detours. Six bridges in the town had been washed out.

Along with the washed out roads and bridges, the town also experienced mudslides and home collapses. A home on East Hill collapsed after having the foundation undercut by Five Mile Brook. The homeowner and her child were able to get out of the house unharmed before the collapse.

Below: Damage in Oxford on the morning of August 19th. Photo by NBC Connecticut:

The town was also the site of a harrowing rescue of 20 people trapped inside of a restaurant. The fire department used a long ladder for patrons and employees to climb across what had become a raging river in the restaurant's parking lot and nearby street. A local market, Market 32, sheltered 100 taking refuge inside. The market offered food, water and dry clothes to those inside.

On the one year anniversary of the floods, the town held a memorial service for Audrey Rostkowski and Ethelyn Joiner, the two victims of the Oxford flood. The town dedicated a memorial plaque to the two near Kirk's Pond. The memorial also includes two benches overlooking the pond and a freshly planted maple tree.

Below: The flood victim's memorial plaque in Oxford, dedicated on the year anniversary:

At the center of the training thunderstorms and flash flood emergency was the town of Newtown. The town reported the most amount of rain, just over 12 inches, most of which fell Sunday afternoon. About 24 hours later, 40 roads in the town remained affected by the floods with 36 sustaining severe damages. Multiple cars were swept off roadways during the storm, but no injuries were reported within the town.

In four separate areas of the town, homes were completely cut off by blocked roadways with residents stranded inside. The town's first priority in road repairs was to get these areas reconnected to main roads. Public works crews worked 24/7 to get roads reopened around the town. Around the town, residents were handing out free coffee the following morning.

Other towns and cities around the area also saw major issues develop. At one point Sunday afternoon, multiple buildings were being evacuated simultaneously in Danbury. A large mudslide within the city led to a gas leak, though this was contained quickly. A wedding venue in Monroe was evacuated after a large sinkhole formed. Monroe was also the site of a rescue of a family trapped within their home. As a whole, the state saw up to 300 million dollars in damages. A year later, much work is left needed to be done.

The weekend of this event saw several weather features, all of which were slow-moving. These features included an expansive upper-level low over the Canadian Maritimes (which has been responsible for rotating weak disturbances into New England this week), surface high pressure (responsible for the longer bouts of pleasant weather), a frontal system to the west and Hurricane Ernesto well offshore.

Below: A graphic we used in a forecast article on August 17th, 2024:

During this weekend, the upper-pattern was favorable for deep, tropical moisture to be advected northward into the northeast. Precipitable water values peaked at around 2 inches, indicating a highly moisture-rich atmosphere. Precipitable water is a measure of water vapor contained in a column of air if it were to be condensed and collected. Basically, the higher the PWAT value, the higher rainfall rates could be, given a forcing mechanism for rain (low pressure system, frontal boundary, etc.) is present.

The high pressure to New England's north and east tried to advect cooler and drier air into the region while the tropical moisture was surging northward. Where these two air masses met would see a warm front set up. This front would provide the focus for training thunderstorms. The warm front happened to set up over southwest Connecticut. Since all these features were slow-moving, the storms were equally slow-moving, resulting in torrential rainfall over the same areas.

As stated at the beginning, some guidance, mainly HRRR, depicted an area of five or more inches of rainfall over southwest Connecticut. HRRR is a short-term, high resolution model that is often the go-to when forecasting in the short-term. This model showed this rainfall during its 6z (around 2am ET August 18) run. However, the model's 12z (8am ET August 18) backed away from this trend. The model trend of more rainfall in Connecticut began on Saturday. This sudden change showed how low-confidence of a forecast this was.

Below: HRRR 6z and 12z model runs from August 18th. Photo by National Weather Service:

Despite this, the trend throughout the week leading up to this event continued to push the higher chances of potential flooding issues farther east, toward, and eventually into, Connecticut. Overall, forecast confidence was not high enough for the National Weather Service to issue a flood watch over Connecticut. For a watch to be issued, there has to be at least a 50% chance that the weather will meet warning criteria, and confidence was just not that high for Connecticut initially. A flood watch was issued Saturday afternoon just to Connecticut's west, where the bulk of rain was initially expected to set up.

Below: Weather Prediction Center's excessive rainfall outlook for August 18th from August 16th (1st image), August 17th (2nd image) and the morning of of August 18th (3rd image):

After the event, questions were raised about two rainfall measurements from the storm in Oxford. Private weather stations recorded measurements of 14.83" and 13.5". These measurements are significant because both were higher than the state's all-time 24 hour rainfall record of 12.77" from the 1955 flood. Because of this, the State Climate Extremes Committee (SCEC) investigated the totals to validate or dismiss this new potential record.

In mid-October, the SCEC, in conjunction with the National Weather Service, finished their investigation and released their review, officially dismissing the totals. Both totals were deemed to be invalid due to where the weather stations were situated. The final report read "One weather station was located too close to trees, which could have affected its readings, while the specifics of the other station`s setup were not able to be verified. Consequently, these observations do not qualify for consideration." With that said, the state's official 24 hour rainfall record does remain 12.77 inches from 1955.