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Mesoscale Discussion 181
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   Mesoscale Discussion 0181
   NWS Storm Prediction Center Norman OK
   1115 AM CST Tue Feb 14 2017

   Areas affected...Portions of western/southern LA and far east TX

   Concerning...Tornado Watch 33...

   Valid 141715Z - 141845Z

   The severe weather threat for Tornado Watch 33 continues.

   SUMMARY...The risk for damaging wind gusts and perhaps a couple of
   tornadoes continues across Watch 33, though the severe potential
   presently appears to be becoming increasingly isolated/conditional.

   DISCUSSION...The latest mosaic radar imagery indicates a broken
   squall line advancing eastward across portions of the lower Sabine
   Valley vicinity, and this activity will continue to spread eastward
   during the next few hours. Cloud tops accompanying the broader
   convective system have been warming based on infrared satellite
   imagery, implying an overall weakening convective trend.
   Furthermore, surface pressure tendencies ahead of this activity are
   small in magnitude. This is likely a reflection of the deeper ascent
   accompanying a deamplifying midlevel cyclonic perturbation lagging
   well to the northwest of richer Gulf moisture serving as inflow to
   the convective system.

   Nevertheless, the latest visible satellite imagery and surface
   observations suggest that a more substantially modified Gulf air
   mass continues advancing inland ahead of the aforementioned
   activity. This air mass is preceded by a marine boundary extending
   around 30-60 miles north of the southern LA coast. Diurnal surface
   heating east of the ongoing convection -- especially where
   mid/high-level cloud canopies are thinning -- may support sufficient
   destabilization amidst this moisture for a conditional severe risk
   persisting into the afternoon.

   The LCH VAD wind profile indicates around 45-50 kt of 0-6-km bulk
   shear with sufficient low-level directional shear for around 200
   m2/s2 of 0-1-km SRH. As such, damaging winds and perhaps some
   tornado potential could conditionally accompany deeper convective
   elements embedded within the squall line -- especially if more
   vigorous updrafts were to become separated within the line.

   ..Cohen.. 02/14/2017


   LAT...LON   29549223 29869397 30849412 31429386 31589350 31429295
               30429235 29549223 

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