Southern Louisiana has been inundated with rain over the past few days; almost two feet have fallen in some areas and widespread flooding has developed. The culprit is a subtropical low, the same system that brought heavy rain to Florida's Gulf Coast earlier in the week.
A persistent dome of high pressure, centered off the Southeast Coast, deflected the low toward the west, where it has churned for several days, pulling in copious moisture from the Gulf of Mexico. Meanwhile, a cold front has approached from the northwest, stalled by the same high pressure dome that shrouds the Southeast. Thunderstorms, firing along the stationary front have brought heavy rain to northern Arkansas, southeastern Missouri and the Ohio Valley region; unfortunately, the tropical moisture plaguing Louisiana will be drawn northward along this frontal boundary, producing more floods along the outer margin of the high pressure dome.
Until the "blocking high" breaks down or moves off to the east, this pattern will continue, exacerbating the floods in Louisiana and fueling torrential rain from Arkansas to New England. Beneath the dome, oppressive heat and humidity persist, relieved only by scattered pop-up showers that merely add more moisture to the steam bath at the surface.