Mesoscale Discussion 1499
   NWS Storm Prediction Center Norman OK
   0909 AM CDT Wed Jul 17 2019

   Areas affected...southeast SD...far southern MN...northeastern NE
   and much of IA

   Concerning...Severe Thunderstorm Watch 514...

   Valid 171409Z - 171545Z

   The severe weather threat for Severe Thunderstorm Watch 514
   continues.

   SUMMARY...Strong to severe storms may continue east/southeast across
   IA through late morning. Storms could re-intensify this afternoon,
   with an accompanying damaging wind threat spreading across much of
   IA and a downstream watch may be needed.

   DISCUSSION...An intense bow echo overnight has continued to produce
   sporadic strong gusts of around 35-50 kt from FSD into northwest IA
   over the least 60-90 minutes. Some weakening has been noted in radar
   and lightning trends on the north end of the bowing segment along
   the IA/MN border. Further south near the IA/NE border some periodic
   intensification has been noted with isolated cells trying to develop
   along the southern flank/outflow boundary across far eastern NE.
   These storms remain in a weakly unstable environment above a capping
   inversion, noted in regional 12z RAOBs. As strong heating occurs
   ahead of the bow (temperatures already in the low 80s across
   south-central IA), strong destabilization will occur, with forecast
   MLCAPE values ranging from around 3000 J/kg across central IA to
   around 1500 J/kg toward the MS River near eastern IA/western IL.
   Strong effective shear will remain oriented along this instability
   gradient as a shortwave impulse crests the Upper Midwest/northern
   Plains upper ridge. Furthermore, thermodynamic profiles indicate
   favorable conditions for a continuation and re-invigoration of
   convection heading into the afternoon with very steep lapse rates
   above a weak EML.

   While there may be a relative lull in convective intensity this
   morning due to weak capping, as heating and further destabilization
   erode the cap, additional development by midday/early afternoon
   could pose a more widespread threat across central into eastern IA.
   Damaging wind gusts and hail are the most likely threat, however,
   forecast hodographs do indicate sufficient SRH with backed low level
   winds through 1km to support some tornado threat. This threat could
   manifest through either mesovortex spin-ups if the bowing line
   segment convective mode persists, or through supercell mesocyclone
   processes if any discrete cells can form. Trends are being monitored
   closely and a new watch downstream WW 514 may be needed in the next
   1-2 hours.

   Additional storms are developing in southern SD, likely atop the
   cold pool with increased ascent due to the eastward migrating
   shortwave impulse. This convection could post an isolated severe
   threat through the morning but longevity of this activity is more
   uncertain.

   ..Leitman/Guyer.. 07/17/2019

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

   ATTN...WFO...DVN...ARX...MPX...DMX...FSD...OAX...

   LAT...LON   43919587 43439250 42569129 41889080 41139123 40969190
               40799326 41049534 41719666 42689805 43219816 43549779
               43849722 43919587