A rare storm for late July will deliver drenching rain and miserable conditions to a large part of the mid-Atlantic and southern coast of New England to end the week.
The rainstorm will be unusual since it will unleash steady rain for 12 hours or more in many locations as it moves slowly across the region. Typically in the summer, rainfall is limited to a few hours in the absence of a tropical rainstorm.
The storm will roll eastward along a zone of temperature contrast with unusually cool air to the north and warm, sticky air to the south.
"This type of setup has the potential to deliver very heavy rainfall and raise the risk of flooding," according to AccuWeather Chief Meteorologist Elliot Abrams.
Motorists from Ohio, Pennsylvania, New Jersey, southeastern New York state, West Virginia, Maryland, Virginia and Delaware are likely to face difficult travel due to persistent downpours, excess water on the road and poor visibility.
Enough rain can fall to cause flash and urban flooding.
Significant airline delays are possible at the major hubs from Pittsburgh to Philadelphia, New York City, Baltimore and Washington, D.C., due to a low cloud ceiling and fog.
Major League Baseball games on Friday and Friday night will be at risk for being delayed or postponed.
"The same storm system will affect the Midwest into Friday with torrential downpours and severe thunderstorms," according to AccuWeather Senior Meteorologist Frank Strait.
Along the southern flank of the storm, severe weather with the risk of damaging winds and perhaps a couple of isolated tornadoes may occur in Ohio and West Virginia on Thursday evening and Virginia, southeastern Maryland and Delaware later Friday into Friday evening.
North of the storm, cool and dry air will prevent rain from spreading across much of upstate New York and central and northern New England.
This cool air will be poised to rush southward in the wake of the storm this weekend.
"Much of the eastern two-thirds of the nation will benefit from the atypical southward intrusion of cooler and drier air that will even reach into parts of the Southeastern states this weekend and into the start of next week," Strait said.
High temperatures are likely to be no better than the 70s F for much of the Northeast on Saturday.
The steadiest rain will retreat to the mid-Atlantic coast and southeastern New England by Saturday morning. However, during Saturday afternoon, showers may crop up east of the Appalachians and migrate toward the coast with perhaps a second dose of rain.
Winds will pick up along the mid-Atlantic and New England coasts on Saturday, which may add to the coolness of the air for a time. As a result, Saturday may not be the best of beach days, even if rain fails to show up for an encore.
With less wind and a return of sunshine, temperatures may rebound to within a few degrees of 80 on Sunday in the Northeast.