AWUS01 KWNH 180858
FFGMPD
ALZ000-MSZ000-LAZ000-181500-

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

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AWUS01 KWNH 221701
FFGMPD
ALZ000-MSZ000-LAZ000-222259-

Mesoscale Precipitation Discussion 0975
NWS Weather Prediction Center College Park MD
100 PM EDT Fri Aug 22 2025

Areas affected...southeastern Louisiana, coastal areas of
Mississippi, far southern Alabama

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

Valid 221659Z - 222259Z

Summary...Spotty/isolated flash flood potential exists with
slow-moving thunderstorms across the discussion area through 22Z/4p CDT.

Discussion...Recent satellite imagery indicates deepening
convection along a variety of subtle low-level confluence
boundaries across the discussion area. Surface heating across the
region has enabled development of 4000 J/kg SBCAPE in the
pre-convective airmass amid 2.2 inch PW values. Deep, efficient
convective process are already supporting spots of 1 inch/hr rain
rates (estimated per MRMS). Additional areas of 1-2 inch/hr rain
rates should develop through the afternoon as additional cells
develop and mergers begin to occur.

The rainfall will occur on locally sensitive areas due to
urbanized/hydrophobic surfaces in/near New Orleans, Baton Rouge,
and Northshore Lake Pontchartrain near Covington and Slidell.
Isolated instances of flash flooding will become more probable
during the afternoon hours.

Much of the convective (and flash flood) threat will be diurnally
driven today, although the degree of convective overturning will
ultimately modulate the spatiotemporal threat of the flash flood
risk through 22Z/4p CDT. Eventually, widespread low-level
stabilization should result in a lower flash flood threat,
although this scenario should take a few hours to play out.

Cook

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

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

LAT...LON 30989045 30788866 30468810 29618895 29148912
28969035 29399160 29889234 30659225

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