Here is an update form the Weather Prediction Center regarding the heavy rain falling across the Pine Belt.
Mesoscale Precipitation Discussion 1072
NWS Weather Prediction Center College Park MD
454 PM EST Thu Dec 27 2018Areas affected…Central Louisiana into Central Mississippi
Concerning…Heavy rainfall…Flash flooding likely
Valid 272153Z – 280353Z
Summary…Increasing risk for significant flash flooding as a line of storms stalls or slowly moves east this evening. Potential exists for an additional 3-4″ (locally higher possible), bringing event totals as high as 8″ in places.
Discussion…As of 22z, a mesoanalysis showed strongly backed flow off the Gulf of Mexico across portions of LA into central MS,while a cold front marched east across eastern TX. The highly convergent flow in the lower levels has continued to funnel in anomalously high moisture (mid/upper 60 dewpoints; PWATs near 1.7″) into the area. Instability remains sufficient and is expected to do so through the evening hours with MUCAPE 1000-1500 J/kg. While the northern end of the squall line, tied to the better mid/upper level forcing, races eastward across northern MS, TN, and KY, the flow will remain more relaxed and parallel to storm motions across LA and southern MS. Finally, GOES-16 mesoscale sector IR imagery over the area shows cloud tops continuing to cool in pockets of deeper convection.
Hi-res models still are not capturing the southern end of the squall line well, being too fast (east) or too north with the axis of heaviest rainfall. Conceptually, based on the environment and current radar trends, the heaviest rainfall is likely to be across central LA into central MS and eventually work its way into portions of west-central AL by mid-evening. While not spatially correct, several hi-res members paint several inches of QPF (HRRR 6-hr QPF ending 04z showing corridor of 3-4″ with locally higher amounts), which seems realistic given the reports so far and the environment that is expected to be maintained for several more hours.
As such, flash flooding is likely across the area and could be locally significant where additional amounts of 3-4″ (locally higher possible) are not out of the question. So far, several mesonet observations have reported 1-hr totals in the 1-2″ range with 6-hour totals ending 22z showing a widespread 2-4″ with some locally higher amounts.
As the soils saturate, any additional rainfall will become problematic especially over sensitive and urban areas. The risk of flash flooding will continue past 04z and additional MPDs may be necessary downstream.
