SPC AC 151959

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0259 PM CDT Sat May 15 2021

   Valid 152000Z - 161200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   CENTRAL/SOUTHERN HIGH PLAINS...

   ...SUMMARY...
   Scattered strong to severe thunderstorms are expected across the
   central/southern High Plains this afternoon/evening. Hail and wind
   are the primary hazards.

   ...Synopsis...
   Most of the forecast remains on track. Relatively minor changes were
   made based on observational trends and are described below.

   ...IA/MN...
   Marginal hail probabilities were adjusted farther south and west.
   Current satellite trends indicate the greatest potential will be in
   central/western Iowa as mid-level drying/subsidence is evident in
   southern Minnesota per water vapor imagery.

   ...Southeastern KS and northern OK...
   Marginal hail/wind probabilities were adjusted based on the current
   position of the differential heating boundary. Storms may develop
   somewhat farther south than previously forecast.

   ..Wendt.. 05/15/2021

   .PREV DISCUSSION... /ISSUED 1140 AM CDT Sat May 15 2021/

   ...Central High Plains...
   West-northwesterly flow aloft exists a broad portion of the region,
   with some tendency for mid-level height rises and subsidence for a
   time over eastern Colorado/western Kansas. Persistent
   easterly/upslope low-level winds will maintain near 50F dewpoints
   across northeast Colorado, yielding MLCAPE values of 1000-1500 J/kg.
   Isolated storms are expected to develop by mid/late afternoon across
   eastern Colorado, spreading eastward and increasing in coverage
   during the evening. Cool temperatures aloft and steep mid-level
   lapse rates indicate that large hail will be the main threat, with
   some increase in potential for damaging wind gusts as the storms
   congeal and spread into Kansas, with aid of a nocturnally increasing
   low-level jet.  

   ...Eastern New Mexico/west Texas...
   A surface dryline will extend north-south across far eastern New
   Mexico this afternoon, with temperatures well into the 80s across
   the region.  Forecast soundings suggest little cap along the
   dryline, leading to scattered thunderstorm development beginning
   around mid-afternoon. Winds in the lower troposphere will be rather
   weak, suggesting storms will be marginally organized with multicell
   and transient supercell structures. The strongest cells will be
   capable of hail and damaging winds, with likely east-southeastward
   persistence into much of west/northwest Texas this evening.

   ...Northern Nevada/northern Utah...
   As an upper low continues to spread southward over California and
   the nearby Great Basin, thunderstorms are expected to redevelop and
   intensify this afternoon along and north of a front across the
   region. Strong/isolated severe thunderstorms capable of gusty winds
   and some hail will be possible.

   ...Upper Midwest including portions Minnesota/Wisconsin/Iowa...
   A few strong/locally severe low-topped thunderstorms may develop
   this afternoon. The region will be influenced by a slow-moving
   shortwave trough and relatively steep lapse rates, with convergence
   and relative potential for thunderstorm development maximized in
   vicinity of a weak boundary. Buoyancy may be adequate in the
   presence of semi-straight hodographs and 45-70 kt anvil-level
   northwesterly winds to support hail potential, particularly late
   this afternoon and early evening.

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