Mesoscale Precipitation Discussion 0030
NWS Weather Prediction Center College Park MD
710 PM EST Wed Jan 24 2024

Areas affected...Southern LA...Southern MS...Southwest/Central AL

Concerning...Heavy rainfall...Flash flooding likely

Valid 250010Z - 250610Z

SUMMARY...Very heavy showers and thunderstorms will drive
significant rainfall totals going through the evening hours across
portions of the central Gulf Coast states. This will drive
numerous areas of flash flooding, including locally significant
and life-threatening urban flash flooding impacts.

DISCUSSION...The early evening radar and satellite imagery shows
an elongated and relatively broken axis of very heavy showers and
thunderstorms impacting the central Gulf Coast region. This
includes large areas of southern LA, southern MS, and areas of
southwest to central AL. The most concentrated activity right now
is over southeast LA just north of Lake Pontchartrain and
extending east-northeast into southern MS to the south of
Hattiesburg. In fact, a Flash Flood Emergency was issued by WFO
Slidell/New Orleans at 2249Z for St. Tammany Parish where already
as much as 4.5 to 6.5 inches of rain has fallen over the last few
hours. Additional concentrated areas of very heavy rain are also
seen developing over south-central LA to the south and east of
Lafayette and Baton Rouge.

A long-lived and well-defined outflow boundary from today's
convective evolution continues to be a key player in the
short-term forecast across the Gulf Coast states heading into the
overnight period. This feature should slow any forward progression
this evening and gradually begin returning north overnight which
will drive a sustained threat of very heavy rainfall across
south-central to southeast LA and over into southern MS.

PWs of 1.75+ inches coupled with MUCAPE values of 1000 to 2000
J/kg will work in tandem with strong effective bulk shear
parameters and a 30 to 40 kt low-level jet to foster organized
convection with rainfall rates that will be capable of reaching or
locally exceed 2 inches/hour. The orientation of the current axis
of convection with the deeper layer mean flow strongly support an
addition cell-training threat, which will greatly enhance the
rainfall potential.

Multiple metropolitan areas including Lafayette, Baton Rouge, New
Orleans, and Hattiesburg will continue to be threatened by
sufficient rainfall for areas of high-impact flash flooding over
the next several hours. This will also spill eastward into areas
of southwest to central AL where rainfall totals will tend to be
somewhat lower, but still sufficient for a threat of flash
flooding.

By late-evening, an additional 4 to 6 inches of rain will be
possible, with locally heavier totals not out of the question.
Given the rains that have already occurred, and with considerable
urban runoff concerns/sensitivities, these rains will foster
numerous areas of flash flooding which will include locally
significant and life-threatening urban flash flooding impacts.

Orrison

ATTN...WFO...BMX...JAN...LCH...LIX...MOB...

ATTN...RFC...LMRFC...SERFC...NWC...

LAT...LON   33448703 33428619 33178576 32458571 31638629
            30658802 30038893 29429048 29319163 29619306
            30249323 30779292 31239179 31859034 32818857
            33168782