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Mesoscale Discussion 1565
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MD 1565 graphic

   Mesoscale Discussion 1565
   NWS Storm Prediction Center Norman OK
   0257 PM CDT Fri Aug 25 2017

   Areas affected...Portions of SD...northern NE...and vicinity

   Concerning...Severe potential...Severe Thunderstorm Watch likely 

   Valid 251957Z - 252230Z

   Probability of Watch Issuance...80 percent

   SUMMARY...The severe-thunderstorm risk is increasing across portions
   of SD and NE, and will continue into the evening. The issuance of a
   Severe Thunderstorm Watch is likely.

   DISCUSSION...Moderate to strong destabilization is ongoing along the
   southern and eastern flanks of a persistent MCV crossing the
   Dakotas, with MCV-related convection suggesting trends of slight
   intensification across parts of north-central SD. Areas of at least
   filtered insolation amidst middle 60s to near 70F surface dewpoints
   is supporting upwards of 2000-3000 J/kg of MLCAPE (aided by steep
   lapse rates aloft) on the warm side of a convectively reinforced
   surface front. This front arcs from northeast SD to the NE/SD border
   west-northwest of Valentine NE. The Valentine surface observation
   indicates temperatures breaching 90F within a warm-thermal axis
   preceding the aforementioned front, resulting in continued erosion
   of antecedent EML-related capping.

   Consistent with the deepening moist boundary layer, cumulus fields
   are becoming increasingly agitated in the vicinity of Cherry County
   NE extending into adjacent SD, and surface-based convective
   development will be likely near the front in the 2030-2200Z time
   frame. This also potentially includes a transition to surface-based
   convection in northeast SD, as ongoing MCV-related convection
   eventually ingests surface-based effective inflow. Given the
   aforementioned magnitude of buoyancy, along with 20-30 kt of
   effective shear (locally enhanced by augmentations to mass fields
   aloft around the MCV), organized convective structures/clusters
   capable of severe hail and wind should spread eastward/southeastward
   into the evening hours. Inflow for this activity, along with some
   southward component to its motion, will be facilitated by a moderate
   southwesterly low-level jet, which will offer sufficient low-level
   shear for a very low chance for a short-lived tornado. However,
   severe hail and wind will be the primary hazards, continuing into
   the evening hours.

   ..Cohen/Grams.. 08/25/2017

   ...Please see for graphic product...


   LAT...LON   42520024 43690050 44899875 44979710 43919646 42589685
               42139799 42520024 

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