Graphic for MPD #0003

Mesoscale Precipitation Discussion 0003
NWS Weather Prediction Center College Park MD
520 PM EST Mon Jan 08 2024

Areas affected...South-Central/Southeast LA...Southern
MS...West-Central/Southwest AL

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

Valid 082220Z - 090420Z

SUMMARY...Areas of very heavy rainfall from training clusters of
showers and thunderstorms will likely impact areas of
south-central LA through southern MS heading well through the
evening hours. Numerous areas of flash flooding are generally
considered to be likely, and this may include a locally
significant urban flash flood threat. Areas of west-central to
southwest AL will see a similar concern later tonight.

DISCUSSION...Very cold convective tops are seen in GOES-East IR
satellite imagery overspreading areas of south-central LA as a
cluster of very heavy showers and thunderstorms moves
northeastward in off the Gulf of Mexico. St. Mary Parish in
particular is seeing some of the heaviest rains currently, but
this activity is expected to grow upscale and maintain a strong
level of organization as it expands off to the northeast over the
next several hours across adjacent areas of south-central to
southeast LA and gradually through southern MS.

In addition to well-defined concerns for severe weather heading
through the evening hours, the evolving convective threat will
include increasing concerns for very heavy rainfall and resulting
areas of flash flooding. A low-level jet of 60+ kts will be
driving very strong warm air advection and moisture transport in
off the Gulf of Mexico as a warm front arrives from the
south-southwest and allows for the arrival of a much more unstable
airmass. This coupled with strong synoptic scale forcing and
enhanced shear profiles will yield clusters of discrete convection
including supercells that in time will tend to merge/organize into
more linear segments capable of training over the same area.

Rainfall rates are expected to increase as stronger instability
arrives this evening and coincides with enhanced IVT values. PWs
are forecast to rise to 1.5 to 1.75 inches, with impressively
convergent and strong IVT vectors with magnitudes reaching upwards
of 1000 to 1250+ kg/m/s in the 00Z to 06Z time frame. A consensus
of the 12Z NAM/GFS solutions in conjunction with the wind fields
from the 12Z HREF guidance would suggest an axis along and
adjacent a line from New Orleans, LA (MSY) through Hattiesburg, MS
(PIB) would be the main corridor for the strongest atmospheric
moisture transport and heaviest rainfall potential going through
the evening hours.

The heaviest rainfall rates should gradually focus over areas of
southern MS where the 12Z HREF supports some 20% to 40%
probabilities of rainfall rates reaching 2 to 3 inches/hour. Storm
totals in general from south-central LA through southern MS are
expected to be on the order of 3 to 6 inches, with some isolated
8+ inch amounts possible in southern MS where there will be a more
organized concern for cell-training which is strongly supported in
recent runs of the experimental WoFS guidance.

Numerous areas of flash flooding are generally considered to be
likely, and this may include a locally significant urban flash
flood threat for some of the major metropolitan areas including
New Orleans, LA early this evening, and gradually areas downstream
over southern MS including Hattiesburg. Later tonight, areas of
west-central to southwest AL will need to be closely monitored for
similar rainfall and flash flooding concerns.

Orrison

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

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

LAT...LON   33018941 32778826 32048777 31048795 30148853
            29608931 29419005 29529093 29829164 30299208
            30959217 31739177 32609078
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Last Updated: 520 PM EST Mon Jan 08 2024