More than a foot of rain could fall on the southern United States over the next week, with some spots on the Gulf Coast seeing more than ten inches of rain yesterday alone. On a scale from "grab an umbrella" to "Jim Cantore's comin' to town," this week will be a solid "build yourself an ark."
A series of slow-moving low pressure systems and their associated fronts will creep across the southern half of the country through next weekend, allowing moist, unstable air from the Gulf to flow landward and result in some pretty juicy convection. Thunderstorms are likely every day through Sunday from Texas to Georgia, with the steepest rainfall totals falling around the northern Gulf Coast. Heavy rains will even creep into the Ohio Valley and the Mid-Atlantic, with flash flood watches already in effect as far north as central West Virginia.
The Weather Prediction Center's latest thinking reflects the chance for heavy rain, with just about everyone from Houston to Evansville to Greensboro expecting at least two inches of rain through next Monday. These are broad-brush totals, of course, and some areas will see much less rain or much more rain than what is forecast above. It just takes one heavy thunderstorm stalling out to create a dangerous flash flood situation.
Yesterday was just the beginning of the event, and some areas saw pretty impressive totals in their gauges by sunrise this morning.
Many residents of Mobile, Alabama, noted that yesterday's thunderstorms were reminiscent of the historic flooding that occurred across the northern Gulf Coast late last April. On April 29-30, 2014, South Alabama and the Florida Panhandle found themselves underneath powerful thunderstorms that just sat and dumped rain for hours on end, leaving some areas cleaning up from unprecedented flooding caused by nearly two feet of rain in just 36 hours. The weather station at the University of South Alabama (from which I graduated—go Jags) recorded three inches of rain in just 23 minutes at the onset of the historic event.
The rain wasn't quite that heavy this time around, but the university's weather station measured nearly six-and-a-half inches of rain yesterday, with radar estimates showing more than ten inches of rain falling across the central part of Mobile County.
NWS Mobile, located at Mobile Regional Airport and just two miles to the west of USA, reported nearly nine inches of rain from the storms. The satellite image at the top of this post shows the thick cloud cover over the coast during the height of the storms.
It'll take rainfall rates of about two to three inches per hour to create the opportunity for flash floods across the areas expecting the heaviest rainfall, so it won't be too hard for these storms to push creeks, streams, and rivers over their banks or overwhelm storm sewers and inundate roads and parking lots. If you come upon a flooded roadway, turn around, don't drown. It takes a surprisingly shallow layer of moving water to overtake your vehicle—most drowning deaths due to flooding occur in vehicles. It's not worth the risk, even if you think (incorrectly or not) that you can make it.