Slight risk for flash flooding across the Midwest tonight, and severe
thunderstorms from the Middle Mississippi Valley to the Northeast on
Tuesday into Wednesday...
Summertime thunderstorms remain in the forecast for parts of the
Southwest and the Southeast/Florida...
Active and unstable weather is expected from the Northern Mississippi
Valley to the Northeast as a broad upper level trough and a series of
surface fronts swing across the northeast quadrant of the country.
A weak boundary moving across the Northeast and the Ohio Valley this afternoon will continue to produce showers and strong to severe thunderstorms along and ahead of it through Tuesday. Behind this, a stronger boundary will move west to east from the Middle Mississippi Valley to the Northeast / Mid-Atlantic.
While scattered rain and storms are likely in the general vicinity of the front, the best chance for organized convection appears aimed for parts of the Mid-Mississippi Valley tonight in an area with plenty of moisture at the surface and good dynamics in the flow aloft.
Locally heavy rain could produce flash flooding overnight in these areas.
On Tuesday and Wednesday, the large area of rain/storms moves with
the boundary from the Ohio Valley to the Northeast/Mid-Atlantic.
Given plenty of moisture and instability ahead of the front, the Storm
Prediction Center has highlighted a wide swath from the Mid-Mississippi Valley to the Northeast for a slight risk for severe thunderstorms.
Elsewhere, the summertime monsoonal flow off the tropical Pacific Ocean continues to keep the widespread showers and thunderstorms in the forecast. As usual, the best coverage of storms should occur during the afternoon and evening hours when diurnal heating is best.
Across the southeastern coast and the Florida peninsula, onshore moisture and sea breeze convergence will allow for the development of showers and storms, especially in the afternoon/evening hours.