Flash flood threat ahead of dramatic cooldown in the Northeast

Yahoo

5 days ago

While not all locations in the Northeast will experience torrential downpours and strong thunderstorms into Friday, areas that do may receive several inches of rain could have to deal with flash flooding, AccuWeather meteorologists warn. Noticeably cooler and less humid air is expected to arrive, offering relief to residents and visitors exhausted by recent heat.
There is a significant amount of moisture in the atmosphere in the Northeast, and that has contributed to flash flooding through the summer, when it has been released in the form of torrential downpours.
For parts of the Northeast, a one-two punch as an approaching cool front and a corresponding ripple in the jet stream will produce precipitation in the form of heavy rainfall into Friday and late this week to early next week in the Southeast.
The first heavy rain and flash flood threat will be an eastward extension of downpours from the Midwest. This band of downpours is forecast to expand from northern Indiana and southern Michigan to northern Ohio, northwestern Pennsylvania and southwestern New York late Wednesday night to Thursday, before weakening and moving out of the region.
At the same time, spotty severe thunderstorms are forecast for parts of the Northeast, but they will not be as widespread as previous severe weather episodes in prior weeks and more recently in the Central states.
A flash flood risk will exist along a significant portion of the mid-Atlantic region to southern New England into Friday as the front and jet stream dip begin to join together. This joint effort will unleash a swath of heavy rain.
The zone from eastern Pennsylvania, northeastern Maryland and northern Delaware to the lower Hudson Valley of New York, including New York City, Connecticut and parts of Massachusetts and Rhode Island is expected to receive 2-4 inches of rain and an AccuWeather Local StormMax™ of 8 inches.
Rainfall of this intensity can easily overwhelm storm drains and flood city streets, subways and poor drainage areas along highways. Major travel disruptions are possible for both I-95 commutes on Thursday, as well as on Friday morning. It can also lead to rapid rises on small streams and a surge of water on rivers, posing risks to campers near creeks and low-lying areas.
A greater concentration of severe thunderstorms packing strong wind gusts is foreseen on Friday from southeastern Pennsylvania and southern New Jersey to the Carolinas.
As torrential downpours, flash flooding and severe thunderstorms focus on the southeastern corner of the U.S. this weekend, much cooler and less humid air will move into the Northeast, resulting in more comfortable air for many. Energy demands will ease, air conditioners can be turned off, and open windows in urban areas will let in cool air for a change.Have the app? Unlock AccuWeather Alerts™ with Premium+
High pressure from central Canada will take control of the weekend in the Northeast in what is usually the muggiest part of the summer.
Typical highs range from the 80s to the low 90s, while nighttime lows range from the low 60s to the low 70s this time of the year. However, as the cool air takes root this weekend, daytime highs will range from the 60s in the mountains to the low 80s in many I-95, mid-Atlantic cities.
Lows will mainly range from 40s in the mountains to the refreshing 60s in most I-95 cities. A few spots may even dip into the 30s over the coldest mountain spots during the weekend.
With the much cooler air heading in, humidity levels will drop significantly, which has been relentless in coastal areas since early June.
"The difference in pressure between the high building into the north and a developing area of storminess along the southern Atlantic coast will create a stiff breeze in some coastal areas of New England and the mid-Atlantic this weekend," AccuWeather Senior Meteorologist Dave Dombek warned.
A steady or gusty northeast wind can stir up the surf and lead to a higher risk of rip currents. While astronomical tides are unremarkable this weekend, the persistent onshore breeze can push water levels to 1-2 feet above typical levels and may lead to minor flooding at times of high tide in low-lying areas.
Next week, the effects of Canadian high pressure will slowly erode, but Monday and Tuesday should continue to provide cooler and more comfortable conditions for sleep, outdoor activities and general relief from recent humidity.
Want next-level safety, ad-free? Unlock advanced, hyperlocal severe weather alerts when you subscribe to Premium+ on the AccuWeather app. AccuWeather Alerts™ are prompted by our expert meteorologists who monitor and analyze dangerous weather risks 24/7 to keep you and your family safer.