Risk of downpours, flash flooding to increase in northeastern US by late week

By Alex Sosnowski, AccuWeather senior meteorologist

May 29, 2018, 2:33:06 PM EDT

A surge of tropical air will cause downpours to spread and the risk of flash flooding to increase over the northeastern United States late this week and into this weekend.

The vast majority of locations will not experience a repeat of the tragic and devastating flash flooding that occurred in Ellicott City, Maryland, from this past Sunday. However, there is the likelihood of isolated flash flooding incidents in the upcoming weather pattern.

From late this week through this weekend, a general 1-3 inches of rain is likely with highly localized amounts up to 6 inches possible.

As the pattern evolves, motorists should be prepared for localized torrential downpours that may quickly flood streets and low-lying portions of highways.

Thunderstorms may gather and strengthen, which may cause airline delays as they converge on the airport hubs.

"The main impact from the downpours will be to deter outdoor activities," according to AccuWeather Senior Meteorologist Brett Anderson.

Rainfall to be indirectly associated with Alberto

While Alberto is forecast to trek northward over the central U.S. and then across interior Canada, more humid air to flow into the Northeast from Wednesday to Saturday.

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Alberto formed near Mexico's Yucatan Peninsula late last week and rolled ashore along the upper Gulf Coast on Monday afternoon as a storm containing both tropical and non-tropical characteristics.

The counterclockwise circulation around Alberto will draw moisture northward from both the Gulf of Mexico and the Atlantic Ocean.

Timetable of rainfall

The best bet for outdoor plans and travel will into the middle of this week, even though the weather pattern supports spotty showers and thunderstorms, mainly during the afternoon and evening hours.

Much of central and northern New England is likely to be free of rain through Wednesday night.

"On Thursday, a more liberal spread of showers and thunderstorms are likely across the mid-Atlantic, central Appalachians, the eastern Great Lakes and western New England," Anderson said. "By Friday, showers and thunderstorms may occur at any time in all but the immediate New England coast."

As the weekend progresses, a push of cooler and less humid air is forecast to advance southeastward from Ontario and Quebec.

While this push may eventually mark an end to showers and thunderstorms over part of the Northeast's interior, it may also enhance the rainfall in some areas for a time this weekend.

For portions of the mid-Atlantic and New England coasts, where humid air may linger, Saturday and Sunday could be the wettest days with an area of drenching rain instead of showers and thunderstorms.