Mesoscale Precipitation Discussion 1073
NWS Weather Prediction Center College Park MD
1151 PM EST Thu Dec 27 2018

Areas affected...southeastern LA into southern MS and central AL

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

Valid 280450Z - 280950Z

Summary...Dangerously high additional rainfall totals of 5-7
inches expected from southeastern LA into southern MS and central
AL through 10Z. This will only worsen ongoing flash flooding
across these areas.

Discussion...04Z radar imagery showed 2 to 3 southwest to
northeast oriented axes of heavy rain located from central LA into
western GA. Training was occurring across LA, MS and western AL
where 850 mb flow was closely aligned with 850-300 mb layer mean
flow supporting weak Corfidi Vector motions, versus farther east
across eastern AL/western GA where 850 mb flow was backed relative
to 850-300 mb mean flow helping allow slow movement of heavy rain
axes toward the east. Observed rainfall of 10 to 11+ inches in
Marion and Walthall Counties in southern MS is aligned close to
KLIX dual pol estimates.

Water vapor imagery through 04Z showed an inflection point over
central LA, located between a weak mid-upper level shortwave over
TX and a departing shortwave over the Mid-Mississippi Valley. As
the weak shortwave over east-central TX continues to advance
toward the northeast through 12Z, only weak mid-upper level height
falls are expected across LA/MS which should only allow a small
eastward movement to the ongoing axes of heavy rainfall among an
otherwise unchanged environment. Given MLCAPE values of 500-1000+
J/kg are forecast to maintain across the central Gulf Coast, and
little change is anticipated in 850 mb direction/magnitude, many
of the same locations experiencing major flash flooding are
expected to continue to receive 1-2 in/hr rainfall rates, locally
higher, over the next few hours with localized maximum additional
totals of 5-7 from southeastern LA into western AL. This includes
the metropolitan areas of New Orleans and along the I-59 and I-20
corridors. A broad 1-3 inches is expected outside of the local
maxima which could cause flash flooding/flooding over already
saturated soils.

Otto

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

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

LAT...LON   34418607 34268524 33558498 32578540 31858657
            31078776 30518854 29339039 29099126 29169233
            29569312 30679258 32259074 33928760