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Mesoscale Discussion 221
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   Mesoscale Discussion 0221
   NWS Storm Prediction Center Norman OK
   0528 PM CST Tue Feb 28 2017

   Areas affected...Central Arkansas into southeast Missouri

   Concerning...Tornado Watch 43...

   Valid 282328Z - 010130Z

   The severe weather threat for Tornado Watch 43 continues.

   SUMMARY...The threat for tornadoes may increase over the next few
   hours across Arkansas into southeastern Missouri, with further
   development into the lower Ohio Valley and western Tennessee later
   this evening.

   DISCUSSION...Multiple clusters of thunderstorms continue to evolve
   across central Arkansas into southern Missouri across the open warm
   sector and driven mainly by warm advection in the low levels and
   lack of substantial capping. 

   Cells over Missouri have shown complex storm structures, with
   several splits noted on radar. This is not surprising given the
   mainly straight-line hodograph on the 20Z observed SGF sounding.
   Also evident steep lapse rates and strong deep-layer shear, which
   support a severe hail threat. As these storms continue eastward,
   they will encounter a more unstable and more sheared environment
   supported by a gradually increasing low-level jet and observed axis
   of mid 60s dewpoints in place. Therefore, potential for stronger
   rotation and right-moving tornadic supercells will increase over
   time.

   To the south, 850-mb flow is a bit stronger and more backed, with a
   cluster of cells west of the Little Rock area showing mesocyclones
   at times, but nothing long-lived thus far. However, the LZK VWP as
   well as objective analysis indicate 250-300 m2/s2 0-3 km SRH in
   place, with an upward trend in GPS PW observations as well. The
   increasing low-level jet will further increase low-level shear this
   evening, favoring tornadic supercells. 

   Model guidance suggests increasing storm coverage spreading eastward
   across the lower Ohio Valley and western Tennessee, with a risk of
   tornadoes this evening. As such, additional tornado watches could be
   required in those areas.

   ..Jewell.. 02/28/2017


   ATTN...WFO...PAH...MEG...LSX...LZK...SGF...SHV...TSA...

   LAT...LON   34369315 34039392 34279444 34489440 37309252 37988947
               37898867 37448838 36818839 36008886 35348933 34959014
               34369315 

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