Atmospheric river triggers life-threatening flooding in Northeast
For the second straight week, parts of the Northeast are facing dangerous flash flooding as another deluge of heavy rainfall slams the region.
Moisture-packed showers and storms will continue to target the Northeast, raising flood concerns into next week.
As more rounds of torrential downpours crawl through the northeastern United States, the likelihood of damaging and life-threatening flash flooding will increase into the middle of this week, AccuWeather meteorologists warn. Flooding may occur in some areas that were hit hard last Sunday and Monday and is also likely in many areas that missed out on the deluge in recent days.
Over the past week, meteorologists at AccuWeather raised concerns about a high-powered rainmaker, known as an atmospheric river, which was forecast to impact the Northeast through the end of the weekend. Flash flood warnings were in effect from portions of Delaware to New Hampshire Sunday as the atmosphere river sent a "fire hose" of moisture into the region as AccuWeather correctly predicted.
This image for Sunday, July 16, 2023, shows the amount of water in the atmosphere that could be unleashed by downpours and thunderstorms. This plume of moisture is forecast to pivot into much of New England Sunday night.
Atmospheric rivers have been responsible for tremendous flash flooding and river flooding in locations such as the Carolinas in years past, as well as in parts of California this past winter on multiple occasions.
Local rainfall amounts of 1–3 inches per hour can quickly overwhelm storm drains and small streams as each round of slow-moving thunderstorms rolls through. This risk will not only be of great concern in suburban and rural areas, but road closures due to flooding may also disrupt travel in some of the major metro areas in the Northeast, including New York City; Hartford, Connecticut; Providence, Rhode Island; and Boston.
Poor weather conditions led to a full ground stop at John F. Kennedy International Airport, La Guardia International Airport and Newark Liberty International Airport on Sunday morning.
A broad area of 2- to 4-inch rainfall is likely in New England and southeastern New York with a pocket of 4–8 inches of rain most likely in central and coastal New England, for cities such as Hartford, Springfield, Massachusetts, and Portland, Maine. An AccuWeather Local StormMax™ of 14 inches is forecast through the duration of the event.
Even a mere 1-2 inches of rain from the storm system will be enough to renew flooding. Given the amount of rain expected by AccuWeather meteorologists, there is the potential for a flooding disaster to occur in some communities.
Severe thunderstorms can be embedded within the heaviest downpours across New England into Sunday evening, and isolated tornadoes cannot be ruled out. A couple of tornado warnings had been issued northwest of Boston early Sunday morning, but no tornadoes have yet to be confirmed.
Some of the major rivers in the region that could be subject to moderate to major flooding amid the deluge are the Connecticut, Merrimack, Charles, Passaic and perhaps the Lehigh, to name a few. At the same time, flash flooding of small streams and low-lying areas is highly likely.
Even in cities farther to the south, in the mid-Atlantic, such as in Philadelphia, Baltimore and Washington, D.C., where torrential downpours may be more spotty in nature, there is still the potential for dangerous and disruptive flash flooding as a result of 1–4 inches of rain. Much of that rain may fall in one or two brief episodes, which could cause rapid and excessive runoff.
Southeastern Pennsylvania in particular has already been hard hit by setups like this. On Saturday, up to 5 inches of rain fell in a localized region in Bucks County, leading to flooding that has claimed at least 4 lives.
AccuWeather forecasters urge motorists to be prepared for street and highway flooding, even in some locations that do not typically take on water due to the extreme nature of the event. Because of the repeating nature of the pattern, some locations can be hit multiple times with flash flooding through Tuesday and perhaps Wednesday.
The risk of flash flooding and river flooding includes some areas that were hit hard by torrential rain from last Sunday to Monday. In a period of several hours to two days, an entire season's worth of rain fell with widespread rainfall of 5-10 inches and locally higher amounts reported in parts of Vermont, eastern upstate New York and western Massachusetts.
Experts strongly urge motorists never to drive through flooded roads. The road surface may have been washed away and swift-moving water may be much deeper than it appears. Campers should use extreme caution when setting up or hiking along small streams as a rush of water from downpours miles upstream could arrive without notice.
Long-range forecast: More rain coming, but also a short break
A break in the heavy rain is likely in the zone from the mid-Atlantic to New England on Monday. The drying out process will begin over the central Appalachians and the mid-Atlantic on Sunday night.
However, runoff will continue in areas that were swamped from the weekend. As water empties into larger tributaries, significant flooding may occur along some of the rivers early this week. There is often a delay in flooding from small streams to larger rivers following heavy rain.
Another round of locally heavy thunderstorms is possible on Tuesday. Downpours from that next storm system will gather over parts of the midwest and Appalachians from Monday to Monday night, where flash flooding may be spotty. Once again as these storms reach the coast, they will slow down, grab extra moisture and potentially unleash more flash flooding.
It is possible that a 48-hour break from widespread rain and thunderstorms will evolve from Wednesday to Friday of this week depending on location in the Northeast.
More rain may be on the horizon for the central Appalachians, mid-Atlantic and New England next weekend. As episodes of heavy rain continue, a familiar problem for the summer of 2023 may return as well -- wildfire smoke.
There is some indication that high-level haze from fires in western Canada may reach the Appalachians during the early and middle part of this week before spreading farther to the east. It is possible that smoke from the fires may begin to reach down to the surface, leading to air quality issues.
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