SPC MD 1734


MD 1734 Image

Mesoscale Discussion 1734
NWS Storm Prediction Center Norman OK
0309 AM CST Thu Dec 27 2018

Areas affected...portions of southeast Texas and
southwestern/west-central Louisiana.

Concerning...Tornado Watch 446...

Valid 270909Z - 271115Z

The severe weather threat for Tornado Watch 446 continues.

SUMMARY...A band of strong/locally severe thunderstorms will
continue to offer a threat for sporadic damaging gusts across parts
of southeast Texas, and a tornado or two cannot be ruled out given
the favorable environment.  A new watch may be needed before the 10Z
expiration time of this one, to cover the potential eastward shift
in severe potential across the Sabine River area.

DISCUSSION...Surface mesoanalysis showed a warm front erratically
winding across southeast Texas from south of LFK to between HOU-BPT,
across the GLS area then eastward over LA shelf waters.  The
relatively cold shelf waters are influencing surface temps between
BPT-GLS and south of LCH.  However, a combination of warm advection
over that shallow layer and vertical mixing should effectively
re-form the warm front over the lower Sabine River region during the
next few hours.  This process will expand the modified marine
sector, with at least marginally surface-based effective-inflow
parcels, eastward ahead of the QLCS described next.

A well-developed QLCS was evident at 09Z from just west of ELD in
southern AR southwestward across the SHV area to near UTS and the
middle Texas Coastal Plain.  A newer line of convection has formed
from its intersection with the original QLCS over eastern
Fayette/Colorado Counties south-southwestward across Victoria
County, with the QLCS weakening to its west.  The combined
convective band is expected to continue moving eastward across and
out of the remaining watch area, into a regime characterized by
MLCAPE 1000-2000 J/kg.  MLCINH increase with eastward extent into LA
but also should decrease with time, as the warm frontal zone
repositions.  50-kt effective-shear vectors and large SRH, as
sampled by VWP hodographs, will support severe potential in the
QLCS, as well as with any relatively discrete/sustained cells that
can be maintained to its southeast, closer to the coast.

..Edwards.. 12/27/2018

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


LAT...LON   29759653 31359451 31649303 30919247 29749305 29759379
            29669385 29689404 29479454 29389470 29349471 29079514
            29259615 29759653 

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