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Mesoscale Discussion 178
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   Mesoscale Discussion 0178
   NWS Storm Prediction Center Norman OK
   0357 AM CST Tue Feb 14 2017

   Areas affected...South-central and Southeast Texas

   Concerning...Severe potential...Watch possible 

   Valid 140957Z - 141230Z

   Probability of Watch Issuance...60 percent

   SUMMARY...A severe threat is likely to develop across south-central
   Texas over the next hour or two. A tornado threat along with
   isolated large hail and wind damage will be possible as a linear
   convective system organizes and moves from eastern parts of the
   Texas Hill Country eastward into southeast Texas this morning.
   Weather watch issuance will need to be considered once the exact
   corridor with the greatest severe threat becomes apparent.

   DISCUSSION...The latest surface analysis shows a cold front
   extending southward from the Dallas/Fort Worth Metro along and just
   east of the I-35 corridor to near Austin where a mesolow is
   analyzed. The front extends southwestward from this surface low to
   near San Antonio where a second surface low is analyzed. A warm
   front extends eastward from this surface low into the Houston area
   with surface dewpoints south of the front across the Texas Coastal
   Plains mainly in the 65 to 70 F range. 

   In addition, water-vapor imagery shows an upper-level trough
   approaching the lower Rio Grande Valley. Increasing large-scale
   ascent ahead of the shortwave trough along with lift associated with
   a developing low-level jet in south Texas will likely result in a
   gradual expansion of thunderstorm activity across south-central
   Texas over the next couple of hours. RAP forecast soundings near and
   to the south of San Antonio early this morning gradually weaken a
   capping inversion near 700 mb which will make conditions
   increasingly favorable for surface-based development. The latest
   HRRR forecast suggests that surface-based storms will first initiate
   along the cold front to the south of San Antonio with this
   convection expanding northward and organizing into a line. MLCAPE
   estimated to be from 1000 to 1200 J/kg along with 40 to 50 kt of 0-6
   km shear will support supercell development with the stronger cells
   embedded in the line. Storm relative helicities of 300 to 325 m2/s2
   evident on forecast soundings will be sufficient for a tornado
   threat associated with supercells. The line of storms is forecast to
   move eastward into the Houston area by late morning where a threat
   for tornadoes, wind damage and hail will be possible.

   ..Broyles/Edwards.. 02/14/2017


   LAT...LON   29179893 28099882 28099802 28639609 29139502 29509496
               29899528 29959661 29729844 29179893 

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