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Mesoscale Discussion 1356
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   Mesoscale Discussion 1356
   NWS Storm Prediction Center Norman OK
   0706 PM CDT Wed Jul 19 2017

   Areas affected...Portions of southeastern SD...northern NE...and far
   northwestern IA

   Concerning...Severe Thunderstorm Watch 422...

   Valid 200006Z - 200130Z

   The severe weather threat for Severe Thunderstorm Watch 422
   continues.

   SUMMARY...Ongoing isolated large hail and damaging wind threat
   across WW 422 remains confined to mainly Holt County NE and vicinity
   in the short term.

   DISCUSSION...Recent radar and visible satellite imagery shows a
   small thunderstorm cluster over Holt County NE which has produced
   isolated large hail and damaging winds over the past hour or so. A
   hot/moist low-level airmass persists along and south of a weak front
   located across northern NE into southeastern SD this evening. Steep
   mid-level lapse rates present on the 12Z sounding from North Platte
   are located across WW 422, which is contributing to strong
   instability (MLCAPE 2500+ J/kg). Although enhanced mid-level flow
   remains mostly to the north of northern NE/southern SD, veering and
   modest strengthening of the wind field with height is supporting
   around 30-40 kt of 0-6 km shear per recent VWP from KLNX.

   The primary thunderstorm cluster across Holt County NE has exhibited
   occasional supercell characteristics, and should continue to pose an
   isolated severe threat for the next few hours as it attempts to
   propagate slowly east-southeastward as a southerly low-level jet
   modestly strengthens this evening across central/eastern NE.
   Additional convection is attempting to develop farther west along
   the surface boundary in northern NE, and may also pose an isolated
   severe threat this evening. The loss of diurnal heating, increasing
   convective inhibition owing to a warm elevated mixed layer, and lack
   of large-scale upper level support all suggest the isolated severe
   risk should slowly diminish later this evening (generally after
   02Z).

   ..Gleason.. 07/20/2017

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...FSD...OAX...LBF...

   LAT...LON   42940204 42959947 43469947 43479591 42179589 42120197
               42940204 

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