Torrential rain and locally gusty thunderstorms will converge on the eastern third of the nation at the end of the week and will raise the risk of flash and urban flooding.
The heaviest and most persistent rainfall and greatest risk of flooding is likely over the Appalachians to the lower Great Lakes region, but a period of torrential downpours will swing through much of the I-95 corridor of the mid-Atlantic and New England as well.
A general 1 to 2 inches of rain will fall along the I-95 corridor with 2 to 4 inches forecast over much of the southern and central Appalachians to the lower Great Lakes. However, locally higher amounts are possible throughout the eastern third of the nation.
As long as the narrow corridor of heavy rainfall continues to move along flooding problems in the I-95 corridor will be minor rather than widespread.
Major cities that will be impact by a six- to eight-hour episode of drenching showers and thunderstorms include Atlanta, Charlotte, Washington, D.C., Baltimore, Pittsburgh, Philadelphia, New York City, Boston and Toronto, Ontario. While the intense rainfall and poor visibility may only last a few hours, the impact on travel and outdoor activities may linger longer.
Atlanta will be hit with the heaviest rain Wednesday night into Thursday morning, while heavy rain can fall during much of Thursday around Charlotte. The greatest risk of flooding downpours around Pittsburgh would be Thursday night.
According to Northeast Weather Expert Dave Dombek, "The timing of the rain is such that Washington, D.C., and Baltimore have the greatest impact Friday morning, while around New York City the worst of the rain will be Friday evening with problems during much of the day around Philadelphia."
The heaviest rain is scheduled to swing through Boston Saturday morning and midday.
Thunderstorms will accompany the heavy rainfall in some areas and can erupt ahead of the steady rain area.
According to AccuWeather Senior Meteorologist Brett Anderson, "The combination of thunderstorms and strong winds aloft could bring gusts to 60 mph on Friday in the mid-Atlantic, especially from eastern Pennsylvania through the Chesapeake Bay region."
Moisture from the Gulf of Mexico, the Atlantic Ocean and the tropics will be drawn into the system as it crawls eastward through Thursday, then begins to lift northeastward Friday into Saturday at a faster past.
"Most areas in the I-95 zone have had a long gap since the last heavy rainfall [late April], so that only minor flooding problems are likely, but it is a different story farther inland and the flooding risk is greater as a result," Dombek said.
Where the heaviest rainfall occurs, over the Appalachians and lower Great Lakes, lives and property can be threatened in some communities that are prone to flash flooding.
As the system passed through the Central states earlier this week, it had a history of causing flash flooding. In addition, the zone of tropical moisture forecast to feed in along the Atlantic coast produced flash flooding and mudslides in Puerto Rico and the Virgin Islands this past weekend.
In the wake of the drenching rain, cooler air will roll eastward from the Midwest in time for the weekend. Similar to a storm that brought cool and unsettled conditions to the area a week ago, this new storm has the potential to bring building clouds and spotty showers mainly during the afternoon and evening hours.
Beneath the storm, high temperatures may be held in the 50s over the mountains and the lower 70s in many areas east of the Appalachians.