SPC MD 1732


MD 1732 Image

Mesoscale Discussion 1732
NWS Storm Prediction Center Norman OK
0139 AM CST Thu Dec 27 2018

Areas affected...portions of northeast Texas...northwestern
Louisiana and southwestern Arkansas

Concerning...Severe Thunderstorm Watch 446...

Valid 270739Z - 270945Z

The severe weather threat for Severe Thunderstorm Watch 446

SUMMARY...Isolated downdraft-wind damage, and perhaps gusts locally
near severe limits, still may occur over the Arklatex region before
the line of thunderstorms moves over progressively more-stable air
and weakens.

DISCUSSION...Surface mesoanalysis shows a Pacific occluded/cold
front extending from a low over northwestern OK across the DFW
Metroplex to near SAT and Eagle Pass TX.  Ahead of that front, a
quasi-linear convective system (QLCS) was moving eastward across the
watch area near an MWT-TXK-ASL line southwestward to between
CLL-UTS, and over the middle Texas Coastal Plain.  A warm front --
denoting the northern rim of the Gulf/maritime-tropical air mass
with relatively uninhibited, surface-based inflow parcels --
intersected the QLCS near UTS, around Walker County TX, extending
southward over the HOU metro and GLS area, then eastward across
southeast TX/LA shelf waters.

Modifications to both the 00Z SHV RAOB and RAP soundings indicate
elevated buoyancy extending 150-250 nm northeast of the warm front,
but over strengthening boundary-layer static stability. 
Accordingly, objective analyses and modified soundings reasonably
show MLCINH around 100 J/kg in the LFK/OCH areas, increasing to over
300 J/kg along I-20 and northward in the watch.  Elevated MUCAPE
around 1000-1500 J/kg is evident within about 75 nm east of the line
over AR, and near the TX/LA border farther south.  While slow
increase in theta-e/buoyancy and decrease in CINH is expected in the
boundary layer, as the warm front moves inland, the QLCS will
outpace that process over AR and northwestern LA, resulting in a
diminishing severe-wind threat eastward and with time in the
Arklatex.  In the meantime, water-loaded downdrafts still may punch
strong/damaging gusts to the surface in a few locales.

..Edwards.. 12/27/2018

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


LAT...LON   32629412 34159357 33889259 33169227 32169277 31909369

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