Mesoscale Precipitation Discussion 0727
NWS Weather Prediction Center College Park MD
1113 AM EDT Thu Jul 17 2025

Areas affected...Southeast Lousiana

Concerning...Heavy rainfall...Flash flooding possible

Valid 171512Z - 172112Z

Summary...The threat of flash flooding will continue across
Southeast Louisiana as thunderstorm bands along the western flank
of 93L backbuild and repeat.

Discussion...Trends in reflectivity over Southeast Louisiana
suggest banded convection on the western side of 93L is
intensifying. Beneath the most intense convective cores located
west of Lake Pontchartrain, recent CREST Unit Streamflows depict
200-400 cfs/smi near an area of 125% QPE-to-FFG Ratios where
repeating of cells with 2-3"/hr rates occurred. As highlighted in
MPD 726, the orientation and repeating of these cells are tied to
an axis of deep-layer moisture convergence focused along the
western flank of the circulation, with very moist and unstable
inflow characterized by 2500-3000 J/kg SBCAPE and 2.3-2.5" PWATs.

Over the next several hours, this low-level convergence axis is
forecast to slowly pivot around the center of 93L while also
becoming more diffuse. Even so, the extremely moist and unstable
environment should favor continued development along this boundary
which could backbuild and repeat owing to favorably oriented
Corfidi vectors directed into the growing upstream instability
pool. 12z CAM guidance -- corroborated by trends in the HRRR --
suggests localized rainfall of 4-6" is possible through 21z in the
highlighted area. While flash flood guidance is high across the
region -- generally in the 4-5"/3 hr range, these higher end
amounts could cause scattered to numerous instances of flash
flooding going into this afternoon.

Asherman

ATTN...WFO...LCH...LIX...

ATTN...RFC...ORN...NWC...

LAT...LON   30809114 30069032 29418921 28858925 28799018
            29179139 29899194 30589178