From the Weather Prediction Center:
Mesoscale Precipitation Discussion 0068
NWS Weather Prediction Center College Park MD
316 PM EST Wed Mar 04 2020Areas affected…southern MS into central/southern AL/GA
Concerning…Heavy rainfall…Flash flooding likely
Valid 042014Z – 050200Z
Summary…Flash flooding appears increasingly likely through the evening hours across portions of central and southern MS/AL/GA. Rainfall rates of 1-2 in/hr will have the potential to produce 2-3 inches of rain by 02Z, with the greatest threat of flash flooding across areas with wetter antecedent soils.
Discussion…20Z VAD wind plots and RAP model data placed an 850 mb front westward from central GA through AL, MS into south-central LA and southeastern TX. Near and north of this boundary and its relatively strong low level convergence axis has been the focus for heavy rain over the past 6-12 hours across the Gulf Coast states from TX through AL. Peak rainfall rates within areas of repeating heavy rain cores have averaged 1-2 in/hr. In addition, the areas that have been experiencing heavy rain early this afternoon are co-located within the northern fringes of a reservoir of MUCAPE with values estimated to be 500-1500 J/kg,
north of the surface front which was located closer to the Gulf Coast. Near and south of the surface front, VAD wind plots and RAP model data showed a broad region of 850 mb wind speeds between 30 and 45 kt from the southwest, helping to transport rich low level moisture to the north.Short term forecasts from the RAP support a slow southward push of the 850 mb front across MS and AL with subtle waves of low pressure riding east along the boundary through 00Z. The orientation of the boundary (low-level convergence axis) will become slightly more SW to NE in the wake of these waves of low pressure which will more closely align the boundary with the average storm motion off toward the northeast. This action will support repeating rounds of heavy rain over the same location from the MS/LA border into portions of AL. As a 700 mb closed low over TX propagates eastward into tonight, the heaviest rain will also push east and south along the Gulf Coast states, overlapping with the southern edges of very low flash flood guidance in central MS/AL (1 inch or less in 3 hours for some locations in MS and AL). 1-2 in/hr rainfall rates appear likely to continue and where repeating of heavy rainfall cores maximize, 2-3 inches can be expected through about 02Z. These additional rains will likely produce areas of flash
In Short
The WPC says it isn’t going to take much rain to create flash flooding. And they expect more rain in the area than it will take to create flash flooding. Thus flash flooding is likely.
This rain will fall between now and about 9pm.
