AccuWeather meteorologists put Northeast on alert for serious flash flood risk
People across the Northeast are encouraged to stay weather aware early this week as a swath of tropical moisture can result in damaging consequences from the Carolinas to Maine. In the hardest hit locations, an entire summer's worth of rain could fall in a matter of a day or two, according to AccuWeather's expert team of forecasters. The likelihood of flooding will extend beyond urban areas and small streams as some rivers will surge out of their banks.
A slow-moving weather system will continue to tap into moisture from the Gulf of Mexico and the Atlantic Ocean as it slowly moves along to the north-northeast into Monday night. This path will direct a swath of flooding rainfall across western and central New England and the northeastern corner of New York.
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On Sunday, high water and flooded roadways were reported in numerous locations throughout eastern and southeastern Pennsylvania, western New Jersey and the Hudson Valley of New York, prompting flash flood warnings across numerous counties. According to local observation sites, rainfall totals of 2 to 4 inches were common. In localized spots, up to 8 inches of rain fell throughout the day and into Sunday night. The heavy rain and resulting flooding led to a fatality in Fort Montgomery, New York.
In Highland Falls, New York, the fire department responded to two people trapped in a vehicle submerged in flood waters.
The heavy rain can add insult to injury for portions of New England where downpours on Friday resulted in the closure of U.S. Route 4 in Killington, Vermont, after a mudslide flung debris across the roadway, making it impassable. Flash flooding was also reported in the Washington, D.C., and Baltimore metro areas, eastern Pennsylvania and eastern New York state to close out last week.
High amounts of moisture available in the atmosphere will make this upcoming weather system a very efficient producer of torrential downpours, AccuWeather meteorologists say.
"Rainfall rates could reach 2 inches per hour in some locations as the system slowly moves," AccuWeather Senior Meteorologist Adam Douty said. "Infrastructure in the metro areas may not be able to handle rainfall of this magnitude, and as a result, rising water could quickly inundate some locations."
In Philadelphia, and New York City, the heaviest rain was mainly confined to Sunday and Sunday evening. While a shower or storm cannot be ruled out early this week, the threat of additional flooding will is low.
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While the heaviest rainfall will stay west of Boston, localized flooding downpours are possible into Monday night.
"Widespread rainfall totals of 2-4 inches are forecast across the Northeast, more localized 4-8 inch totals. Rainfall will be particularly heavy in Vermont, where between 8 and 16 inches of rain can fall." DaSilva said, noting that an AccuWeather Local StormMax™ of 18 inches couldn't be ruled out in the Green Mountains.
The historical average rainfall for the entire month of July is generally between 3 to 4.50 inches for the major cities across the Northeast. During this event, some locations could pick up that entire amount within a few hours. Within 24 hours, an entire season's worth of rain can fall.
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Motorists are likely to face significant slowdowns as a result of poor visibility and possible road closures. The amount of rain forecast will not only heighten the risk of street flooding but also lead to rapid rises along small streams, which can then spill over their banks.
In a number of locations, conditions may be as bad or perhaps worse than during Irene's impact in late August 2011. Enough rain will run down through streams to lead to flooding. Moderate flooding is forecast along the upper portion of the Connecticut River, while some of the secondary rivers in Vermont and New Hampshire may experience waters rising to major flood levels.
The moisture-laden air will ram into the mountains of eastern upstate New York and western New England, resulting in an enhancement of downpours in the higher terrain. Air that hits mountain ranges is forced to rise upward, and that upward motion results in an enhancement of clouds and precipitation.
"We are closely monitoring the risk of mudslides in the Green Mountains of Vermont. The heaviest rain is forecast to fall across the Green Mountains and that, combined with the rain that fell on Friday, can increase the chance of dangerous mudslides in the mountains," DaSilva said.
AccuWeather meteorologists say downpours will gradually ease from southwest to northeast into Tuesday as the weather system responsible for the deluge shifts into Canada.
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A slight reduction in humidity levels across the interior Northeast early this week will offer a brief reprieve from the stifling conditions of late. Hot weather with high humidity will be quick to rebound as the week progresses, however.
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