Frequent rounds of rain may escalate into serious flood threat for Northeast into August

By Alex Sosnowski, AccuWeather senior meteorologist
July 22, 2018, 5:12:35 AM EDT

A pattern of persistent downpours, beginning with a rainstorm this weekend is likely to disrupt travel, hinder outdoor plans and projects and put summer heat on hold in the Northeast into early August.

The pattern may escalate into a serious flood threat for some communities this week.

A rainstorm moving up from the south will coincide with a shift in the jet stream and mark the beginning of an extended period of wet, humid conditions in the East.

The storm will force drenching rain northward across the mid-Atlantic and into New England through Sunday.

The rain can be heavy enough to cause a period of flooding in urban and low-lying areas. Small streams can rise out of their banks.

On Saturday night, downpours prompted flash flooding and water rescues from northern Virginia to Maryland. Preliminary rainfall totals exceeded 4 inches in part of this corridor.

The combination of drenching rain and gusty winds could cause sporadic power outages along the coasts from the Delmarva Peninsula to Long Island, especially where strong thunderstorms may become intertwined with the storm system.

Into Sunday morning, the soaking rain is expected to continue to spread northward from the Chesapeake Bay area into New York state and southern New England.

Sun NE 7.22 AM

"On Sunday, the rainstorm will become more spread out with one pocket of downpours around Buffalo, New York, and Toronto, Canada, as rain soaks parts of New England," according to AccuWeather Senior Meteorologist Kristina Pydynowski.

People with outdoor plans or heading to the beach this weekend should be prepared for wet weather during part of their trip. The combination of rain and poor visibility may cause vehicle traffic to slow to a crawl at times. Airline travelers should prepare for more delays.

The combination of rain and windy conditions may seem more like a nor'easter from the spring or autumn in places such as Norfolk, Virginia; Ocean City, Maryland; Atlantic City, New Jersey, and New York City.

Second storm to move in from the central US

At the same time farther west, a storm from the Plains will create a swath of rain and thunderstorms over the Midwest to the southern and central Appalachians. This is the same storm system that produced severe weather on Thursday and Friday in the Central states.

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This storm is expected to return showers and thunderstorms to Pittsburgh; Roanoke, Richmond and Norfolk, Virginia; Washington, D.C.; Dover, Delaware; and Philadelphia on Sunday. A shower or thunderstorm may also push back into New York City in the afternoon.

Extended period of wet weather in Northeast likely to evolve into a flooding situation

As AccuWeather long-range meteorologists have been suggesting since early July, the overall weather pattern will become conducive for rounds of wet weather and an increased risk of flooding in the Northeast.

Such an extensive pattern of wet weather is highly unusual for the middle of summer, without a tropical storm, according to AccuWeather Founder, President and Chairman Dr. Joel N. Myers.

East Downpours 7.22 AM

"The same southward dip in the jet stream that develops over the North Central states and frequently funnels unseasonably cool air into the Midwest is likely to often pull moisture northward along the Atlantic coast," according to AccuWeather Lead Long-Range Meteorologist Paul Pastelok.

Since there is the risk of 10 inches of rain or more falling on some locations, serious flooding is likely to evolve in some communities.

As the pattern evolves, downpours that drenched areas last Tuesday and hit some locations this weekend may be a sample of what may occur in the coming weeks.

While the pattern may not bring rain every day everywhere, rainfall is likely to be above average, and people may get frustrated by the frequency of showers and thunderstorms as far as outdoor plans, sporting events and construction projects are concerned.

Enough rain is likely to fall in many areas to wipe out any rainfall deficit this summer.

Incidents of flooding are likely, since it could rain hard enough long enough.

"The pattern is likely to have staying power through the end of July and may persist well into August," Pastelok said.

Small streams may surge to bank full and large rivers may even approach flood stage in some cases. Locations prone to flash flooding should be extra vigilant.

When asked if long stretches of sunny, hot days are over in the Northeast for the season, Pastelok responded with, "It's probably more likely that summer is going to take a long break with some hope for sunny, hot weather during the middle to latter part of August."

"There will be still be some very warm days during the wet pattern, when the sun is out for several hours."

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