SPC AC 271259

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0759 AM CDT Mon May 27 2019

   Valid 271300Z - 281200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
   MIDWEST AND THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Severe thunderstorms, including a risk for tornadoes, severe hail
   and damaging wind gusts, are expected across the Midwest this
   afternoon into tonight including eastern Iowa to northern portions
   of Illinois/Indiana. Severe storms are also expected across the
   central High Plains, and perhaps southward through the Texas South
   Plains on a more isolated basis.

   ...Midwest including eastern Iowa to northern Illinois/Indiana...
   Related to a northeast-moving (perhaps convectively augmented)
   shortwave trough, a ribbon of flattening/strengthening mid-level
   westerlies will overspread the region this afternoon and evening.
   These strengthening low/mid-level winds will overlie a
   northeast-shifting surface low across northern Iowa to southwest
   Wisconsin/northwest Illinois, a west/southwestward extending front
   across Iowa, and a northward-shifting front principally across
   northern portions of Illinois/Indiana. 

   That said, some uncertainty exists concerning warm front positioning
   later today and peak destabilization/most probable zone of initial
   surface-based thunderstorm development owing to persistent bands of
   convection (decayed MCS) across Iowa/northern Missouri this morning,
   with related factors of lingering cloud cover and some impact on
   upstream trajectories owing to the overnight MCS. Regardless, a
   trend of steady northward-moistening and destabilization is expected
   this afternoon with the warm front, and as clouds erode, upwards of
   2500-3000 J/kg MLCAPE is plausible by late afternoon within the warm
   sector across eastern/southern Iowa and northern/central Illinois
   into central Indiana. 

   Initial surface-based storm development is expected across eastern
   Iowa/northeast Missouri into northwest Illinois this afternoon.
   Within a moist/moderately unstable environment, supercells can be
   expected amidst ample hodograph length/curvature with upwards of
   40-50 kt effective shear. Winds within the lowest 1-2 km AGL will be
   diurnally strong and the potential will exist for tornadoes,
   particularly near the warm front where low-level/deep-layer shear
   will be maximized. Large hail can also be expected. Severe storms
   are likely to develop generally eastward particularly across
   northern portions of Illinois/Indiana through the evening.

   ...Central High Plains/Nebraska/far northern Kansas...
   A prominent upper trough will shift east-northeastward over the
   southwestern deserts toward the Four Corners area through tonight. 
   Height falls will occur into the central High Plains in tandem with
   a general strengthening/backing of mid-level winds as an upper jet
   exit region overspreads the region. In response, surface
   cyclogenesis will intensify across eastern Colorado with easterly
   low-level upslope flow modestly increasing across northeast
   Colorado/southeast Wyoming into western Nebraska. 

   Initial surface-based thunderstorm development by around
   mid-afternoon is anticipated near/just east of the front range of
   northern Colorado and southeast Wyoming, with storms subsequently
   developing/increasing east-northeastward into the Nebraska Panhandle
   through late afternoon/early evening. Although low-level
   moisture/buoyancy will not be robust, upwards of 750-1250 J/kg
   MLCAPE in the presence of 50+ kt effective shear (accentuated by
   very strong southwesterly anvil-level flow) will support supercells
   capable of large hail (at least a few 2+ inch diameter hailstones
   plausible). Large hail aside, a couple of tornadoes may occur. 

   Farther to the east/southeast, into southern Nebraska/northern
   Kansas, surface-based deep convective development is a little more
   uncertain through peak heating, with a more conditional overall
   severe/supercell risk late this afternoon/early evening. Of somewhat
   greater certainty is the possibility of development toward/after
   sunset, including the possibility of gradual upscale growth across
   Nebraska this evening in vicinity of the roughly west/east-oriented
   surface boundary. In such a scenario, with aid a nocturnally
   strengthening low-level jet, a damaging wind/large hail risk could
   increase across central/southeast Nebraska and far northern Kansas
   during the evening and overnight hours.

   ...West-central Kansas, OK/TX Panhandles, Texas South Plains...
   While confidence is not particularly high across this region, some
   concern exists for very isolated but potentially intense storms late
   this afternoon/early evening, with some possibility that available
   guidance/convection-allowing models are too muted with little or no
   suggested deep convective development. At the very least, a
   conditional supercell risk will exist. 

   Some uncertainty exists related to impacts of prior-day convection
   and convective overturning across Kansas and western Oklahoma/Texas
   Panhandle, but some elevated mixed-layer reestablishment should
   occur during the afternoon. Convective inhibition may become very
   weak by the 21-23Z time frame in vicinity of the north-south
   dryline, with mid-level temperatures not expected to be overly warm
   (8C to 10C at 700mb across western Kansas and the Panhandles;
   warmest south). While uncertainty exists, if/where sustained deep
   convection forms, the environment will likely be conducive to
   supercells with a risk for severe hail/wind and possibly tornadoes.

   ..Guyer/Broyles.. 05/27/2019

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