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Mesoscale Discussion 99
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   Mesoscale Discussion 0099
   NWS Storm Prediction Center Norman OK
   0822 PM CST Sat Jan 21 2017

   Areas affected...Portions of northern Louisiana...southern
   Arkansas...and central/southern Mississippi

   Concerning...Tornado Watch 17...18...

   Valid 220222Z - 220415Z

   The severe weather threat for Tornado Watch 17, 18 continues.

   SUMMARY...Severe thunderstorms will continue to develop into Watch
   18 over the next hour. Across northern portions of the watch, the
   main severe hazard will likely transition to damaging winds (with a
   tornado or two possible). Farther southeast in Mississippi, a
   greater tornado/large-hail potential will exist, with a strong
   tornado possible.

   DISCUSSION...In response to increasing warm advection related to the
   low-level jet, severe thunderstorms near the LA/AR border have begun
   to grow upscale into a broken band, with embedded mesocyclones still
   noted. This evolution should continue as the storms progress into
   Watch 18, resulting in damaging winds likely becoming the dominant
   threat across northern portions of the watch. A tornado or two will
   still be possible, however, considering the amplifying low-level
   flow and notable veering with height of 0-3-km winds.

   Farther southeast over south-central Mississippi, dew points in the
   lower 60s will favor slightly greater surface-based buoyancy. KDGX
   VWP data suggest around 250-300 m2/s2 of storm-relative helicity is
   present for low-level mesocyclone organization. With increasing
   semi-discrete convection over the next several hours, the tornado
   potential should rise accordingly, and a strong tornado (primarily
   closer to the MS/AL border) cannot be ruled out.

   ..Picca.. 01/22/2017


   LAT...LON   32099280 32719344 33029341 33969225 33749036 32938851
               32258847 31648881 31278954 31399119 31489220 32099280 

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