Mesoscale Precipitation Discussion 0741
NWS Weather Prediction Center College Park MD
457 AM EDT Fri Jul 18 2025

Areas affected...Southeast LA...Coastal MS/AL...

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

Valid 180900Z - 181500Z

SUMMARY...Eastern side of 93L; highly unstable, moist and
favorable repeating/regenerative flow regime may result in narrow
but highly focused streets of intense rainfall 2-3"/hr and spots
of 2-5" resulting in focused incidents of possible inundation
flooding.

DISCUSSION...08z surface analysis suggest weak surface low resides
between Baton Rouge and Lake Pontchartrain; while GOES-E SWIR
shows low-level cloud elements shifting from SSW to N across
southeast LA toward the MS/AL coast.  Additionally, the loop shows
a low level 850-700 axis of vorticity/wind shift is curling along
the apex of the tropical wave crossing E LA into S MS.  VWP shows
winds at MSY and HDC are veering in response.  RAP analysis
suggest 925-700mb flow is aligning through depth along the Bird's
Foot across the Chandeleur Island toward the coast as well with
15-25kts increasing through depth.  Thermodynamic profiles show
very warm Gulf waters are shifting parcel ascent paths to support
narrow skinny unstable profiles with SBCAPEs nearing 3000 J/kg. 
With weak upstream confluence combined with frictional
convergence, scattered thunderstorms with cooling tops are
breaking out across far SE LA.

Updrafts are back-sheared with increased upper-level outflow given
SSW to NNE cell motions while upper level outflow is toward the SW
(out of northeast); helping to maintain updraft strengths.  As
noted the confluent surface to 850mb flow off shore, vertically
stacks across the area of concern with and enhanced axis over far
SE LA of 2.25-2.4" (slightly less further north and west between
the surface low and mid-level vort center even further west.   As
such, thunderstorms within the corridor will be very efficient
with deep warm cloud process and rates of 2-3"/hr are likely. 
Upstream convergence, enhanced by coastal frictional convergence
at the surface will support the best ability for increased
rainfall totals given back-building or regenerative nature.  As
such, spots of 2-5" are possible, particularly just north of the
coastlines of SE LA into S MS and AL. Intersecting urban locations
are at particular risk of rapid inundation flooding through 15z;
though overall coverage within the area of concern is likely to be
limited due to the nature of narrower streets/convergence bands.  

Gallina

ATTN...WFO...LIX...MOB...

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

LAT...LON   31008846 30918824 30618801 30208809 29788841
            29048914 28968971 29048981 28989033 28929069
            29069116 29359120 29519094 30009017 30298987
            30738934 30998882