Rounds of showers and thunderstorms will bring the threat of flash flooding and travel disruptions from the Ohio Valley to the mid-Atlantic and New England through Friday.
The risk area covers a heavily populated and heavily traveled region of the country, home to tens of millions of people and daily commuters.
A surge in humidity, combined with a very slow-moving front and a series of disturbances moving along it, will favor episodes of downpours, thunder and lightning.
While most of the region will just experience a few doses of heavy rain and thunder, some locations can be hit much harder on one or more occasions through the end of the week.
Cities that could be directly impacted by flash flooding include Cincinnati, Washington, Baltimore, Philadelphia, New York City, Boston, Hartford, Conn., and Portland, Maine.
The pattern is part of the same setup that will continue to clobber the central Plains this week.
It has the potential to bring a couple of inches of rain in as many hours to a few communities in the Ohio Valley, mid-Atlantic and New England as well. Some unlucky locations could be hit with 6 inches of rain into the end of the week.
Similar to what occurred in June and July in the Northeast, some streets and highways could be flooded.
The activity will not be limited to the afternoon and evening hours, which is typically the case this time of the year.
Motorists and airline interests should be prepared for delays.
Over the weekend, the corridor of repeating downpours will shrink southward, so that much of New England, the northern mid-Atlantic and part of the Ohio Valley will dry out.
However, that southward shift will grind to a halt. Flooding problems are possible from Kentucky and Tennessee to the Appalachians in Virginia, West Virginia and Maryland Saturday and Sunday. There is a chance the activity continues on to the coastal plain in Virginia, Maryland, Delaware and southern New Jersey as well.