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ACUS11 KWNS 311302
SWOMCD
SPC MCD 311302
MSZ000-LAZ000-ARZ000-311500-

Mesoscale Discussion 1746
NWS Storm Prediction Center Norman OK
0702 AM CST Mon Dec 31 2018

Areas affected...Louisiana and southern Mississippi

Concerning...Severe potential...Watch possible

Valid 311302Z - 311500Z

Probability of Watch Issuance...60 percent

SUMMARY...Showers and the occasional thunderstorm will continue this
morning, gradually increasing in coverage and intensity. A damaging
wind gust or brief tornado may be possible with the strongest
activity. In the near term, the threat remains too marginal and
spatially limited for watch consideration. However, later this
morning a watch may become necessary as convection
develops/intensifies along the Pacific front.

DISCUSSION...Showers continue to develop this morning across
Louisiana and southern Mississippi within a zone of isentropic
ascent within a warm-conveyor regime. Despite 12Z soundings from
across southern Louisiana suggesting mixed-layer CAPE around 1000
J/kg, poor midlevel-lapse rates and tall, skinny CAPE profiles have
not produced strong enough ascent for charge separation. Even absent
lightning, ongoing convection is developing within a strongly
sheared environment, leading to episodic rotation within some of the
stronger showers. Although low-level buoyancy is somewhat limited,
near-neutral low-level-lapse rates may support the potential for a
damaging wind gust or brief tornado through mid morning.

Later this morning stronger mid-level ascent will begin to overtake
the Pacific front moving into far western Louisiana at present.
Despite low-level wind fields remaining somewhat backed behind the
Pacific front as low-level mass fields respond to stronger surface
pressure falls across Oklahoma, a modest increase in low-level
convergence along the Pacific front will combine with the increasing
synoptic ascent to strengthen convection along the front and support thunderstorm development. Expectation is that a narrow band of
thunderstorms will develop across portions of central Louisiana and
lift north-northeast. Again, strong wind fields in the presence of
modest instability and near-neutral low-level-lapse rates will
support an isolated damaging wind gust or brief tornado.

..Marsh/Grams.. 12/31/2018

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...JAN...LIX...LCH...SHV...

LAT...LON 30529296 32909181 33668874 30758965 30529296



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