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Mesoscale Discussion 1340
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   Mesoscale Discussion 1340
   NWS Storm Prediction Center Norman OK
   0244 PM CDT Tue Jul 18 2017

   Areas affected...Portions of Nebraska and northeast Colorado

   Concerning...Severe potential...Watch unlikely 

   Valid 181944Z - 182215Z

   Probability of Watch Issuance...20 percent

   SUMMARY...The area is being monitored for increasing severe
   potential this afternoon, with activity spreading
   eastward/southeastward into the evening. Present indications are
   that Watch issuance will be unlikely, though environmental and
   convective trends will continue to be monitored.

   DISCUSSION...Widespread insolation amid middle 60s dewpoints on the
   immediate cooler side of a northeast-southwest frontal zone across
   NE into northeast CO is supporting moderate to strong
   destabilization. The 12Z North Platte NE sounding indicates
   relatively steep mid-level lapse rates accompanying an
   elevated-mixed-layer plume, overlying the post-frontal moisture,
   yielding around 2000-3000 J/kg of MLCAPE -- given diabatic
   surface-layer heating. This heating is aiding in the erosion of
   post-frontal MLCINH. Meanwhile, baroclinic circulations are being
   enhanced on the warm side of a post-frontal differential-heating
   zone across west-central and northwest NE, with recent convective
   development noted near North Platte. Multi-layered cloud decks
   reinforcing the differential-heating zone are likely related to weak
   mid-level ascent preceding the southwestward-trailing portion of a
   shear-axis aloft. The aforementioned differential-heating, and
   shear-axis-related ascent, along with frontal ascent, will all
   contribute to an increase in convective coverage and intensity
   across portions of western NE and northeast CO during the next few
   hours, with activity spreading generally eastward and southeastward
   into the evening hours.

   Given the aforementioned magnitude of buoyancy, intense updrafts and
   downdrafts capable of producing isolated severe wind and hail will
   be possible. However, generally modest mid-level flow strength,
   associated with 20-30 kt of effective shear, should tend to mitigate
   convective organization and severe coverage. If cold-pool
   amalgamation were to eventually yield upscale convective growth,
   some potential for a greater severe-wind risk may eventually evolve
   into parts of central/eastern NE. However, confidence in this
   scenario is presently limited owing to the modest magnitude of deep
   shear.

   ..Cohen/Hart.. 07/18/2017

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

   ATTN...WFO...OAX...GID...LBF...GLD...BOU...CYS...

   LAT...LON   40890325 41650172 42249988 42519855 42309777 41329780
               40719921 40200138 39990281 40400337 40890325 

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Page last modified: July 18, 2017
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