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Mesoscale Discussion 1169
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MD 1169 graphic

   Mesoscale Discussion 1169
   NWS Storm Prediction Center Norman OK
   0214 PM CDT Wed Jun 28 2017

   Areas affected...Much of central and southern Iowa and adjacent
   portions of northwestern Ilinois...northern Missouri and
   southeastern Nebraska

   Concerning...Severe potential...Watch likely 

   Valid 281914Z - 282115Z

   Probability of Watch Issuance...80 percent

   SUMMARY...A rapid increase in thunderstorm activity and intensity
   appears possible late this afternoon, perhaps as early as the 3-5 pm
   CDT time frame.  The latest trends are being closely monitored for
   increasing severe weather potential which likely will require a
   watch issuance.

   DISCUSSION...Potential convective evolution late this afternoon
   remains a little unclear, but objective analysis suggests that
   mid-level inhibition is becoming increasingly negligible across much
   of the region.  This is occurring in response to both continued
   insolation and low-level moistening, with surface dew points
   currently increasing through the upper 60s and lower 70s F.  Beneath
   a corridor of modestly steep mid-level lapse rates, associated with
   a thermal ridge extending east northeast of a plume of warmer and
   more strongly capping elevated mixed-layer air across the central
   Plains, moderately large mixed layer CAPE (2000-3000 J/kg) appears
   to be developing.

   Given this magnitude of potential instability, in the presence of
   weakening inhibition, rapid thunderstorm development and
   intensification appears possible within the next few hours.  Forcing
   for ascent to support initiation, however, remains a bit unclear. 

   Deepening convective development is currently evident along the
   surface trough axis, to the west of a persistent area of elevated
   thunderstorm activity now spreading east northeastward across north
   central Iowa.  Additional attempts at deepening convective
   development also appear ongoing around and east of the Omaha area,
   beneath a somewhat warmer mid-level environment, in the presence of
   enhanced lower/mid tropospheric warm advection.  As a lingering
   mid-level speed maximum (associated with larger-scale upper
   troughing shifting into the Upper Midwest) gradually noses east of
   the mid Missouri Valley late this afternoon, a general increase in
   convective development seems probable, in the presence of sufficient
   vertical shear for supercells, and, eventually, an upscale growing
   thunderstorm cluster or two.

   ..Kerr/Guyer.. 06/28/2017

   ...Please see for graphic product...


   LAT...LON   41709558 42559466 42409363 42649219 42179114 40609089
               40099460 40599631 41709558 

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