Mesoscale Discussion 1804
   NWS Storm Prediction Center Norman OK
   1105 PM CDT Mon Aug 19 2019

   Areas affected...Portions of western/central IA...far southeastern
   SD...far southwestern MN...and far eastern NE

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

   Valid 200405Z - 200600Z

   Probability of Watch Issuance...80 percent

   SUMMARY...A threat for mainly large hail should increase over the
   next couple of hours as storms increase in coverage and intensity.
   Severe Thunderstorm Watch issuance is likely.

   DISCUSSION...A well-defined surface warm front extends eastward from
   a low over western SD across southern SD, roughly along the NE/IA
   border, and into southern IA. Warm air advection is occurring atop
   this front as a southwesterly low-level jet gradually strengthens
   late this evening. The VWP from KOAX has shown an increase in the
   0-2 km layer over the past couple of hours, generally to around
   30-35 kt above 1 km. Ascent associated with this low-level jet has
   encouraged elevated showers to develop across parts of northwestern
   IA, with a few recent lightning strikes noted with this activity.

   The 00Z sounding from OAX showed very steep mid-level lapse rates
   (around 8.6 C/km in the 700-500 mb layer) associated with an EML
   were present across this region. These lapse rates aloft coupled
   with ample low-level moisture are supporting moderate to very strong
   instability along and to the cool side of the front (MUCAPE of
   2000-4500+) per latest mesoanalysis. Westerly winds strengthen with
   height through mid levels, and a subtle vorticity maximum along the
   NE/SD border maximum noted on water vapor may provide an additional
   source of lift to encourage at least scattered storm development.
   Around 40-50 kt of effective bulk shear will likely remain across
   this region through the overnight hours, which will support
   supercells initially. Given the large degree of elevated instability
   and strong shear present, robust updrafts appear likely. Large hail
   should be the primary hazard with initial storm development, with
   these storms likely remaining elevated above a near-surface stable
   layer to the cool side of the surface front. However, there is some
   potential for upscale growth into a MCS later tonight across parts
   of central IA, which could result in an eventual damaging wind
   threat materializing. Watch issuance is likely in the next couple of
   hours to address the initial large hail risk.

   ..Gleason/Grams.. 08/20/2019

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

   ATTN...WFO...MPX...DMX...FSD...OAX...

   LAT...LON   42999379 42499378 41829411 41399485 41359556 41539614
               42029655 42799688 43569680 43709587 43659501 43559445
               42999379