About a week ago, southern Louisiana began to experience heavy rainfall from a storm system that remained relatively stationary over the Gulf Coast. The SPoRT-LIS, a real-time, high-resolution implementation of the the NASA Land Information System, captured trends in soil moisture that provide some insight into the evolution of this flooding, including hints at precursor conditions that may have led to the extreme nature of this event.
The 0-200 cm integrated relative soil moisture (RSM) fields have been used in the past to identify flood precursor conditions. These fields give an indication of the total amount of water in the soil moisture column and provide information about how much additional precipitation can be accepted by the soil before all becomes runoff into nearby streams and rivers. About 2 weeks ago (August 3 00Z; Fig. 1), Southern Louisiana showed soil moisture values in the 50% range, which are higher than other parts of the country, but likely about normal given the swampy nature of that region. However, following a couple of precipitation events in that area on August 3, 7, 9, and 10), these integrated RSM fields bump up the 60-65% range (Fig. 2), which has become somewhat of an unofficial threshold for antecedent saturated soils that could lead to areal flooding events. Based on various reports, it appears that the official start of the flooding event began on August 11.
Starting on 11 August, the 0-200cm integrated RSM begins to exhibit signs of flooding (starting to get into 70-80%; not shown). By Aug. 12, most of SE LA is above 80% Integrated RSM with pockets above 90% (not shown). By Aug. 14 (Fig. 3), nearly all of southern Louisiana is covered with soil moisture values above 85-90%, which indicates major ongoing flooding in this area.
These products are provided to select National Weather Service partner offices to aid in these flooding forecast challenges. For more details on this product and to view additional days or hours, please visit the real-time SPoRT-LIS page.