Thunderstorms dumped two months’ worth of rain in the Northeast Kingdom of Vermont on Tuesday morning, with 8 inches coming down in just six hours. A dire flash-flood emergency was issued for the town of St. Johnsbury, about 60 miles east of Burlington, as roadways turned into raging rivers.
“Homes have been washed away,” the National Weather Service in Burlington wrote in its urgent emergency bulletin. “Cars are underwater. Some roads have been washed out. Check on the safety of your friends and neighbors.”
Flooding was reported in several areas of northeast Vermont, including around Lyndonville, about eight miles north of St. Johnsbury, where the Weather Service received a report of several homes destroyed. In East Burke — about five miles north of Lyndonville — a road was washed out and multiple cars submerged.
There was also flooding in Brighton State Park and the town of Morgan in far northern Vermont, where weather radar estimated more than half a foot of rain had fallen.
Advertisement
The flooding was largely a surprise, with forecasts only calling for widely scattered showers and thunderstorms. Any flood risk wasn’t anticipated to come until Wednesday.
Around St. Johnsbury, a single thunderstorm blossomed near the core of a low-pressure system transiting the area. It erupted around 11 p.m. and dumped 1.99 inches on St. Johnsbury between midnight and 1 a.m. Then came another 5.7 inches over the next three hours.
In just four hours, 7.79 inches of rain was recorded. July’s average monthly rainfall is 4.43 inches.
An incredible amount of rain fell across portions of northeast Vermont overnight. Here's a zoomed in view of the reports we've tallied. The highest amount of 8.41" was recorded by one of our CoCoRaHS observers in St. Johnsbury. pic.twitter.com/sj80mqsXNA
— NWS Burlington (@NWSBurlington) July 30, 2024In some such instances, thunderstorms can become “terrain-locked,” or hover over a single mountain or mountain range as air is forced uphill, enhancing a storm. That wasn’t a factor here.
“I don’t think the terrain actually had much influence just because the low-level wind fields were quite light,” said Pete Banacos, the science and operations officer at the Weather Service in Burlington.
Advertisement
While the storm dumped a total of 8.04 inches on St. Johnsbury before dissipating, 0.15 inches fell before midnight. That means 7.89 inches will go in the books for Tuesday. That obliterates the previous single-day record of 4.99 inches that has stood since July 28, 1913. Less than three weeks ago, the town recorded 4.93 inches of rain as Hurricane Beryl’s remnants worked through the region on July 11, also causing flooding.
Share this articleShareThis also qualifies as a “thousand-year rain event” for St. Johnsbury, meaning that rain that heavy has only a 0.1 percent chance of falling in any given year, according to data from the National Weather Service. The threshold for a thousand-year rain event in St. Johnsbury is 4.32 inches in three hours, or 5.43 inches in six hours. St. Johnsbury got 5.8 inches in three hours and 7.96 inches in six hours, outpacing even those extreme thresholds.
“It’s off the charts,” Banacos said.
It’s only the second time in Banacos’s memory that his office issued a flash-flood emergency. He noted one issued on July 10, 2023, during an “atmospheric river” event when a fire hose of tropical moisture dumped 4 to 8 inches across northern Vermont.
Advertisement
This time around, the torrents were far more localized.
It’s been an active stretch for flooding in Vermont. Nearby Lyndonville was damaged “quite severely” by flooding from Beryl, according to Banacos, and more flooding may be on the way.
“Tomorrow [Wednesday] looks problematic,” he explained. “We have a slow-moving [low-pressure system] over the eastern Great Lakes that will be pushing eastward. It really depends where the embedded thunderstorms track, but we’re worried about tomorrow for potential additional flooding.”
Every column of atmosphere, he explained, will contain close to 2 inches of moisture — which could mean torrential tropical downpours.
While no single event can be attributed to human-caused climate change, and thunderstorms are largely a random process, it’s well-established that the frequency and intensity of rainfall extremes are increasing. As the atmosphere continues to warm, it can hold more water — meaning that during high-end rainfall events, greater rainfall rates, and subsequently increased rainfall totals, are probable.
Jason Samenow contributed to this report.
ncG1vNJzZmivp6x7uK3SoaCnn6Sku7G70q1lnKedZMSmrdOhnKtnYmV%2FdXuPcGZsaF%2BbubC7w2acpp2inLKvr9hmrZ6qnaS7tXnJqJ%2Bnq5Kqv7p50Z6aqKqUZA%3D%3D