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ACUS11 KWNS 202009
SPC MCD 202009

Mesoscale Discussion 0079
NWS Storm Prediction Center Norman OK
0209 PM CST Fri Jan 20 2017

Areas affected...portions of the middle and upper Texas coast

Concerning...Severe potential...Watch possible

Valid 202009Z - 202215Z

Probability of Watch Issuance...40 percent

SUMMARY...Isolated thunderstorms will continue to develop into the
late afternoon and evening across the middle and upper Texas coast.
Additional development eventually is expected across eastern Texas,
but timing of more widespread convection is a bit uncertain.
Initial concerns this afternoon will be hail and some strong wind

DISCUSSION...Isolated thunderstorms were developing along the middle
TX coast near VCT, in the vicinity of a warm front draped northeast
to southwest across the coastal plain. Weak destabilization is
occurring as temperatures warm into the upper 60s to upper 70s with
weak capping eroding. Latest hi-res guidance indicates coverage
should remain rather isolated for a few hours, before a gradual
increase occurs into the evening hours. This seems reasonable given
a weak shortwave impulse is currently moving across the TX Big Bend
area and will provide increasing forcing for ascent in the coming

In the meantime, isolated strong to severe thunderstorms will be
possible during the next few hours in the vicinity of the surface
boundary. Forecast RAP soundings coupled with mesoanalysis data show
steep low and midlevel lapse rates improving between now and 00z. At
the same time, increasing vertical shear, with long hodographs
suggest large hail will be the main concern as storm track along to
just north of the surface boundary. Some backed low level flow in
the vicinity of the boundary will lead to some enhanced shear in the
lowest 1 km or so, posing some low-end tornado potential. However,
wind speeds less than about 10-15 kt in this layer will limit
greater tornado threat. With low level lapse rates increasing to 7-8
C/km, a few strong wind gusts also will be possible. While coverage
is expected to remain limited in the short-term, a watch may be
needed in the next 1-3 hours, depending on convective trends.

..Leitman/Hart.. 01/20/2017

...Please see for graphic product...


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