Louisiana under a flooding emergency (H. Michael Mogil, CCM, CBM, DMS)
Early this Saturday morning, many parts of southern and central Louisiana were under a flooding emergency. Widespread 10 to 20 inch rainfall totals (Fig. 1) 
have led to flooding and flash flooding with some places under evacuation orders and others dealing with water reaching and entering homes and businesses. The National Weather Service (NWS) has been passing on information from emergency management officials and also adding some of its own strong wording. One NWS office even urged listeners not to, “drive cars through flooded areas. Remember, two feet of rushing water can carry away most vehicles including pickups. Turn around and don`t drown!”
The culprit behind this flooding situation is a slowly moving low-pressure system, albeit with a weak meteorological wind circulation (Fig. 2). The low formed just south of Florida’s “Big Bend,” northwest of Tampa, last weekend and brought some heavy rainfall to places in Florida; however, most of its more active convection remained over Gulf of Mexico waters. Coupled with sea level pressure readings remaining near average global values (29.92 inches of mercury), the low stood little chance of developing into a tropical storm.
Then, during the past few days, as the low drifted slowly to the west, the precipitation region keyed on Louisiana and remained there. As seen in Fig. 1, rainfall totals have been extraordinary.
NWS precipitation forecasters are not painting a rosy picture for Louisiana. For the next few days, parts of the state could see general rains approaching 10 inches, with a predicted weekly total of more than 13 inches (Fig. 3). Locally, amounts could easily be double these, given the high atmospheric moisture values in the region and the system’s slow movement. 
Widespread flooding will continue, even if rainfall tapers off, because rains already fallen have entered upstream watersheds and will be making their way downstream toward the Gulf of Mexico. Flooding can even develop in a downstream under clear to partly skies.
The low-pressure system will continue to plod slowly westward and some of the system’s moisture is expected to interact with a frontal system to the north of Louisiana. Hence, parts of the Ohio and Middle Mississippi River Valleys (and even parts of east Texas) could see excessive rainfall during the upcoming week.
© 2016 H. Michael Mogil
Originally posted 8/13/16