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Mesoscale Discussion 188
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   Mesoscale Discussion 0188
   NWS Storm Prediction Center Norman OK
   0200 PM CST Sun Feb 19 2017

   Areas affected...Parts of north TX and southern OK

   Concerning...Severe potential...Watch possible 

   Valid 192000Z - 192230Z

   Probability of Watch Issuance...60 percent

   SUMMARY...The severe threat is expected to continue increasing
   through 22-23Z (4-5 PM CST), with large hail and perhaps a couple of
   tornadoes the main threats expected. Watch issuance is possible.

   DISCUSSION...Low-level convergence is weak along an ill-defined
   dryline/cold front feature extending north-south across much of west
   TX early this afternoon. Regardless, as a southern-stream shortwave
   trough/low approaches the southern Plains from the west this
   afternoon and evening, large-scale forcing for ascent should
   gradually increase across north TX and southern OK. Although
   widespread cloudiness has hampered diurnal heating somewhat south of
   a warm front located across north TX/southern OK, continued
   low-level warm air advection and earlier clearing this morning has
   allowed surface temperatures to generally warm into the upper 60s to
   low 70s across this area. Adequate low-level moisture to the south
   of the warm front, with surface dewpoints in the low to mid 60s,
   will support convective development/maintenance.

   A modestly steepened mid-level lapse rate plume will persist over
   the discussion area through this evening, and combined with
   sufficient low-level moisture, a corridor of weak to moderate
   instability (500-1500 J/kg MLCAPE) is present across much of
   central/north TX into southern OK, decreasing with northward extent.
   Largely unidirectional southerly flow strengthening with height is
   occurring across the same general area in association with the
   approaching mid-level trough/low. Effective bulk shear values of
   40-60 kt will easily support supercell structures. Some backing of
   the low-level wind field to southeasterly will be possible across
   parts of north TX into southern OK per latest RAP guidance, as a
   southerly/southeasterly low-level jet is forecast to strengthen
   across the eastern fringes of the discussion area by early evening
   (around 00Z).

   Initial convective development will likely occur by 22-23Z as
   convective inhibition erodes with continued modest daytime heating
   and low-level moistening. This activity should be mainly discrete
   supercells posing a large hail threat, with some initial storm
   splits likely given the largely unidirectional flow. If storm mode
   can remain mostly discrete into the early evening hours while
   remaining surface based, then the possibility for a couple tornadoes
   would increase as the low-level jet strengthens and effective SRH
   likewise increases. Eventual upscale growth into a QLCS with some
   wind threat appears probable by mid to late evening.

   ..Gleason/Guyer.. 02/19/2017


   ATTN...WFO...FWD...OUN...SJT...

   LAT...LON   32699971 34459927 34929857 34949780 34659721 33999705
               33439703 32259716 31789737 31539793 31519900 31689969
               32699971 

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Page last modified: February 19, 2017
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