43 million face life-threatening flood risk in the Northeast

AccuWeather

AccuWeather flooding expert Alex Sosnowski was live on the AccuWeather Network on July 31 to discuss the flash flood risk in the Northeast.

Transcript

00:00Joining me right now is ACCUA, the flooding expert, Alex Sosnowski.

00:04You know, Alex, we're talking off camera about this.

00:08We're going to show you the rainfall map here in a second.

00:10And this kind of a rainfall map to me is a little unusual for the area and scope for this time of the year.

00:20Yeah, especially without a tropical system trying to help things out.

00:24What you got going on, though, as you pointed out, is that front is lifting the air.

00:30OK, it's lifting the air.

00:31And the jet stream pattern is causing the downpours that are generated, the thunderstorms that are generated to repeat line up in streets.

00:39And it's going to kind of leaf out into a mosaic pattern here like you see.

00:43And that kind of rainfall that we're showing there, that broad area, two to four inches,

00:47that's equivalent pretty much to the entire rainfall for all of July in these places.

00:52Wow.

00:53Now, flash flood guidance.

00:55What we're going to talk about now is how much rain has to occur to produce widespread flash flooding.

01:03It will begin in eastern Pennsylvania, northern, northeastern Maryland.

01:07And I mean, it's a pretty high threshold, isn't it, for flash flooding?

01:12Yeah, it is.

01:14The sun this time of the year is brutal.

01:16It dries the topsoil out.

01:17And that can have a huge effect on this.

01:20But what this doesn't account for, when we talk about the flash flood guidances,

01:24it doesn't account for paved surfaces.

01:26There's a lot of pavement in the Mid-Atlantic, in the northeast, a lot of rooftops.

01:30And that creates rapid runoff.

01:33So this type of rainfall here, we're going to be close to these thresholds here for flash flooding in all cases.

01:40In some cases, we're going to exceed it.

01:42In some cases, we'll come in a little bit shy.

01:44But the thing to point out here is we look at that one-hour rainfall.

01:48You may get close to two inches of rain in a half an hour.

01:52And then another downpour, that moves on, and another downpour comes along.

01:55So you're accumulating that rainfall and repeating it.

01:59What about New York City?

02:00Notice, and I think perhaps what you just mentioned, the threshold here is much lower.

02:05Yes.

02:06You can notice here that the rainfall amounts here, the threshold is a lot lower.

02:11Plus, we have a lot of pavement, a lot of rooftops around New York City.

02:16What I can tell you here looking at this is if you're working a day shift,

02:21I know you had an excuse there to stay home, work from home.

02:24If you're working a day shift and you're already committed to go to work,

02:28this is a day you want to leave early.

02:29If you're working a second shift, you'll probably want to come into work early if you can't work from home.

02:36I want to end with the flash flood guide in southwestern Massachusetts, Connecticut.

02:41It's kind of in between New York City and what we saw across eastern Pennsylvania.

02:46Yeah, all these rainfall amounts are significant here, and I think we can get close to all of these here.

02:51In some places, we're going to exceed the threshold, and some places come in a little bit shy.

02:56But if you're prone to flooding, if you drive along a stretch of road that drains poorly,

03:01when these downpours kind of go through, generally from 6 p.m. to midnight, I think, is when the bulk of this stuff is going to hit,

03:08that's when you can run into problems here.

03:10The roadway could be flooded, and you can run into problems.

03:13You could ruin your car.

03:14More importantly, you could put yourself in a life-threatening situation.

03:17Really quickly, I know you do have some concern across the southeast as we head into the weekend.

03:23Yeah, if you look at the rainfall totals here for this event coming up, pretty much targeting the weekend here,

03:29the amounts are almost double what we're going to see in the northeast here coming up Thursday into early Friday.

03:35This stuff in the southeast here is going to be especially nasty.

03:38There's some tropical connection to it over time.

03:43But if you look at the downpour area there, there's a broad area where we have 2 to 4 inches of rain forecast,

03:48and there's a good patch there where 4 to 8 inches of rain is coming with an AccuWeather storm max of 12 inches.

03:54And probably about half of that can occur in several hours.

03:57So this is a big problem for these places, whether you need the rain or not.

04:01There's going to be some flash flooding problems with this.

04:04Definite dangers on the roads.

04:06AccuWeather flooding expert Alex Znausi, thanks for joining us here on AccuWeather Early.

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