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Mesoscale Discussion 1004
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   Mesoscale Discussion 1004
   NWS Storm Prediction Center Norman OK
   0902 PM CDT Mon Jun 12 2017

   Areas affected...Portions of western/central NE...northeastern into
   east-central WY...and western/central SD

   Concerning...Tornado Watch 317...320...

   Valid 130202Z - 130300Z

   The severe weather threat for Tornado Watch 317, 320 continues.

   SUMMARY...A threat for a few tornadoes and scattered large
   hail/damaging winds continues across valid portions of WW 317/320.
   Parts of WW 317 have been locally extended in time until 03Z based
   on latest radar trends.

   DISCUSSION...Two semi-discrete supercells continue across western NE
   as of 02Z. The southernmost storm has had multiple tornado and large
   hail reports associated with it over the past several hours. A
   strongly unstable airmass into central NE/southern SD, where MLCAPE
   ranges from 2500-3500 J/kg per 01Z mesoanalysis, will very likely
   support continued severe-caliber storms into the late evening.
   Strong effective bulk shear values of 50-60+ kt owing to a
   northeastward- moving upper low over the northern Great Basin will
   also contribute to robust updraft organization, with all severe
   hazards remaining possible. A short-term (next hour or two) tornado
   threat should be maximized across parts of western NE into far
   southwestern SD with the previously mentioned semi-discrete
   supercells. Across this area, strongly veering/strengthening
   low-level winds are contributing to a relative maximum in effective
   SRH values (300-500+ m2/s2).

   Additional convection has recently formed along northern portions of
   the Laramie Mountains in east-central WY, and this activity may also
   pose some severe risk, although instability is weaker with northward
   extent. Current expectations are still for ongoing storms to grow
   upscale into one or more bowing line segments as they move into
   north-central NE and western/central SD later this evening. If this
   were to occur, then damaging winds would likely become the primary
   severe threat.

   ..Gleason.. 06/13/2017

   ...Please see for graphic product...


   LAT...LON   41020272 41100329 41900340 42350351 42600475 42540599
               44910592 44930127 44280046 43679980 42150023 41020272 

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