Mesoscale Precipitation Discussion 0034
NWS Weather Prediction Center College Park MD
457 AM EST Fri Jan 26 2024

Areas affected...southeastern LA into southern MS

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

Valid 260955Z - 261555Z

SUMMARY...An increase of heavy rain with periods of training is
expected early this morning across southeastern LA into southern
MS. Flash flooding will be possible from rainfall rates to
potentially peak in the 1-2 in/hr range, falling on top of
locations which received heavy rain with in the past 2 days.

DISCUSSION...0930Z GOES East infrared satellite imagery with
lightning data overlaid showed a cluster of thunderstorms 50 to
150 miles south of the eastern LA coast. Longer loops of satellite
data with surface observations overlaid showed the presence of a
composite outflow boundary in the central Gulf of Mexico (south
and east of the thunderstorm cluster). However, station plots in
the northern Gulf have largely returned back to southerly flow,
helping the advection of low level moisture back toward the
central Gulf Coast and making the outflow's presence less
impactful. Of key importance, the 850-700 mb layer in LPW imagery
has shown a notable northward advance of higher moisture across
southern LA since 05Z. Given the mid-levels are not likely to have
significantly changed since 00Z, the 700-500 mb lapse rate from
00Z LIX sounding showing 7 C/km is likely still valid across the
central Gulf Coast region.

As an upper level shortwave trough continues to advance east from
eastern TX over the next 6 hours, low level winds in the 925-850
mb layer out ahead of the upper trough across the central Gulf
Coast are expected to back, helping further with the transport of
low level moisture into southeastern LA and southern MS, eroding a
dry layer seen on the 00Z sounding from LIX and recent RAP
analysis point soundings in the area. Given fairly steep mid-level
lapse rates, low level moisture advection should result in the
rapid development of uninhibited MUCAPE of 500 to 1000+ J/kg later
this morning. Low level warm advection beneath the divergent right
entrance region of a 100-120 kt 250 mb jet max is likely to
support the increase of showers and thunderstorms, perhaps as
early as 12Z, across southern LA into southern MS. Southwesterly
steering flow may align with similarly oriented low level
convergent axes in the 925-850 mb layer, supporting periods of
training. While there remains uncertainty with convective vigor,
especially with recent runs of the HRRR backing off on QPF totals
through 15Z, the thermodynamic and kinematic environment will be
capable of 1-2 in/hr rainfall rates.

According to Multi-Sensor MRMS estimates, 4 to 8 inches of rain
has fallen over portions of central/southern LA into southern MS
within the past 48 hours. This had led to saturated soils in some
locations which will be more vulnerable to flash flooding from
additional heavy rainfall. The possible addition of 1 to 3 inches
of rainfall through 16Z may lead to renewed areas of flash
flooding across southeastern LA into southern MS.

Otto

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

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

LAT...LON   31398952 30778919 30008916 29189008 28949084
            29199160 29339265 29729268 30219182 30579123
            31349022