Flash flood risk extending from New England to mid-Atlantic

AccuWeather

Flooding downpours will bring a significant flash flood threat to the Northeast region of the U.S. This could lead to potentially life-threatening conditions as well as severe travel disruptions.

Transcript

00:00Baltimore, Washington, D.C., Philadelphia, New York City, and in the southeast of New England.

00:06All right, joining me right now is AccuWeather Chief Meteorologist Jonathan Porter.

00:09You know, John, just came on our radar late last week, and then over the weekend,

00:14we got more and more confident, and then we made the call about this flood risk on Monday.

00:21That's right, Bernie.

00:22AccuWeather experts have been having this in our forecast,

00:25talking about the risk for flash flooding in the mid-Atlantic and the northeast since Monday,

00:30days ahead of all other known sources so that people can be best prepared and stay safer.

00:35We're concerned about this setup because of the reasons you talked about.

00:40There's sunshine outside already in Baltimore, building instability, fuel for these thunderstorms,

00:45and they're going to be slow-moving, Bernie, which means persistent downpours

00:49at a significant flash flood risk in major cities.

00:52As you know, one of my favorite tools is the water vapor loop here, John,

00:55and there's a reason for that because we'll first start.

00:57Here's the front.

00:58You can see where it is from northern New England back toward the Midwest.

01:03So there it is at the surface, but the reason it moves is the steering flow

01:10in the middle and upper part of the atmosphere.

01:12What's the steering flow?

01:14Unfortunately, the steering flow isn't perpendicular to the front, John.

01:18It's parallel.

01:20That is, it's moving west, southwest to northeast, and that means that front's not in a hurry to push south.

01:27No, and this is actually a very concerning setup that we see when we look at the water vapor loop here

01:31because look at all these greens and darker blues here.

01:35This is indicative of higher levels of atmospheric moisture.

01:39And notice it's going from southwest to northeast parallel with that front.

01:43So there's nothing to give it a push and keep it moving.

01:46That's why we're concerned about that moisture training over the same areas with these slow-moving storms,

01:52and that's a recipe for trouble.

01:53And dry air, look at that dry air.

01:55New York City, Harrisburg, Washington, D.C.

01:58So right now, that means the sun is out.

02:01And as you mentioned, that makes the atmosphere even more unstable.

02:05But we have another ingredient, another ingredient.

02:09Of course, we have the dew point temperatures well in the 60s and 70s here, John.

02:12But this is a lot of energy in our upper air map to come in across this part of the country this time of the year.

02:20It sure is.

02:21And what we're talking about here is spinning the atmosphere with these oranges and red colors.

02:26And out ahead of those areas of spin, that's where the air wants to be lifted, producing clouds and rain, heavy rain in this case.

02:35And this is a lot of jet stream energy for this time of the year.

02:38This is a more typical setup, more of like spring or early or fall.

02:44So to get this with such high levels of atmospheric moisture, that's the worrying setup here.

02:49Yeah, there's the dew point temperatures, 70 degrees in New York City, 76 in Harrisburg, 77 in Washington, D.C.

02:55All right, let's take a look at the future radar here.

02:58This is the latest.

02:59This is what's concerning by the time we get in the early afternoon.

03:03Right, it's not going to take too long.

03:04Look at this, 2.30 on the eastern time on the future radar here.

03:08Look at these reds and yellows already developing across southeastern Pennsylvania, parts of New Jersey.

03:13These are heavy thunderstorms that are going to be producing rain rates of 1 to 3 inches per hour.

03:19And more important than the amount of rainfall, the total amount of rainfall, is how fast that rain is falling.

03:25That's too fast, too furious, and that's going to result in significant flash flooding concerns.

03:30This is the kind of setup that can, in a major metro area like New York City, as soon as that rain rate gets above an inch and a half per hour,

03:37that's when we get flooding in the subways and streets, also creek and stream flooding in the more rural areas.

03:43And there can even be in the higher terrain of northeastern Pennsylvania or the Berkshires of western Massachusetts,

03:48some rock slides or mudslides in hard-hit areas.

03:52You know, John, we were talking with our flooding expert, Alex Zasnowski, and he made a point.

03:56This is an unusual amount of rain over a larger area for this time of the year that is not associated with a tropical system.

04:07It is unusual.

04:08Two to four inches of rain over a wide area from parts of New England through the mid-Atlantic states

04:13with an AccuWeather local storm max of eight.

04:15And so such unusual amounts of rainfall lead to a higher risk of flash flooding.

04:20Move to higher ground if you get flash flood warnings for your community,

04:24especially if you live along a creek, stream, waterway, or other low-lying area.

04:29And the flash flood threat's a little dangerous for New York City, John,

04:32because we feel pretty certain that we're going to easily get one to two-inch rain amounts here per hour in some of these storms.

04:38Exactly, and that's all it's going to take to produce significant flash flooding.

04:41All right.

04:42AccuWeather Chief Meteorologist Jonathan Porter.

04:44John, thanks for breaking it down here on AccuWeather Early.

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