A Tweet from NBC Connecticut Chief Meteorologist Ryan Hanrahan.
THE VALLEY – The rain and subsequent floods Sunday (Aug. 18) that killed two people and caused untold damage in Oxford and Seymour was an extreme weather event, to say the least, according to a meteorologist interviewed Monday by The Valley Indy.
The amount of rain that fell (anywhere from nine to 12 inches depending on the town) coupled with the time it took to fall (roughly six to eight hours) made it either a once in every 500 years – or a once in every 1,000 years – event.
That means, according to the U.S. Geological Survey, a flood of Sunday’s magnitude “has a 1 in 1,000 chance of occurring in any given year. In terms of probability, the 1,000-year flood has a 0.1% chance of happening in any given year.”
The storm was birthed from an area of low pressure that crossed the Great Lakes and moved through New York and Pennsylvania, according to Gary Lessor, the chief meteorologist at Western Connecticut State University in Danbury.
The forecast as late as Saturday called for rain in New York, New Jersey and Pennsylvania, Lessor said. An inch or so of rain was in the forecast for Sunday, with heavier rain on Monday.
“Nothing said Connecticut was going to get hit with anything like this,” he said. “We just had what was likely a very small area of low pressure that developed and just kept funneling low-level moisture into southwest Connecticut . And obviously, it stalled.”
The fact the storm crawled so slowly to the east was a surprise, Lessor said.
“There was just no indication on the (computer weather) models it would be this far east. It wasn’t until this was actually occurring that they even picked up on the scenario,”
he said. “There was already five inches of rain down, and then suddenly the models were saying, ‘Hey, you could have another five inches of rain coming.’ Unfortunately it was already underway, there was already flooding. It was too little, too late.”
Lessor’s comments were echoed on Twitter by Ryan Hanrahan, the chief meteorologist at NBC Connecticut. He also said the computer models just didn’t pick up on the localized flooding.
“Our forecasts are much better than they were 10 years ago, but localized events like this one can still happen with little warning,” Hanrahan posted. “Frustrating for sure and another example of where we need to keep improving.”
*Editor’s Note: the first paragraph was changed to accurately reflect that statistical information.
