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Mesoscale Discussion 1565
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   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 www.spc.noaa.gov for graphic product...

   ATTN...WFO...FSD...OAX...ABR...LBF...UNR...

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

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Page last modified: August 25, 2017
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