Excessive rainfall discussion from WPC-
South/Central Appalachians/OH Valley/Mid-Atlantic/Northeast...
Multiple rounds of showers and thunderstorms will move across the region ahead of an approaching cold front from the northwest. Ahead of this boundary, very moist and unstable air will be in place. Some weak impulses moving atop this environment should support scattered to widespread convection. Precipitable water values will climb to around 2 inches aided by light southwesterly flow. This is around 1.5-2 standard deviations above the mean. Instability will be modest with MUCAPE values around 1000 J/kg. While convection is expected to move at a decent pace eastward, multiple rounds moving over pockets of lower FFG could result in isolated flash flooding across this region. Not to mention, as the front starts to sag south across southern New England, the propagation vectors will align with the mean wind parallel to the front. This will result in training of convection in some locations. Given this and the convection observed from yesterdays activity, a Marginal Risk was expanded across a large portion of the Northeast/Mid-Atlantic southward into southern Appalachians and north into the OH Valley. Worked with the local offices and coordinated an upgrade to a Slight Risk across much of the central/southern Appalachians where HREF probabilities were fairly decent and FFG values were fairly low.