SPC AC 081620

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1120 AM CDT Sat May 08 2021

   Valid 081630Z - 091200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
   EVENING INTO EARLY TONIGHT FROM NORTHEAST KS INTO EXTREME NORTHWEST
   MO...

   ...SUMMARY...
   Scattered severe storms are expected later this afternoon through
   late evening across northern Kansas, and overnight into northwestern
   and central Missouri.  The initial Kansas storms will pose a large
   hail threat, with an increase in the damaging-wind threat by early
   tonight.  A few tornadoes will also be possible late this evening
   into tonight.

   ...KS this afternoon/evening into MO overnight...
   In advance of a midlevel trough now approaching western CO, a lee
   cyclone will develop east-southeastward from eastern CO into
   southwestern KS through this afternoon, as a dryline sharpens
   southward near the western OK border, and a warm front consolidates
   near I-70 across KS.  Moisture return in the warm sector has been
   delayed by a prior frontal intrusion related to a midlevel trough
   near the Atlantic coast, with the richest moisture (> 65 F
   dewpoints) confined to south of I-20 in east TX as of late morning. 
   Moisture advection will continue through the day from OK into KS,
   but will be offset by vertical mixing, resulting in boundary-layer
   dewpoints mainly in the 50s immediately east of the dryline up to
   the triple point in KS.

   Regional 12z soundings suggest surface temperatures will need to
   approach 90 F to mix deeply enough to eliminate convective
   inhibition, and this only appears probable in a narrow zone along
   the dryline to near the triple point by mid-late afternoon. 
   High-based thunderstorm development is expected near and just
   northeast of the triple point in west central KS by 21-23z, and
   storms will subsequently move east-northeastward along the surface
   warm front.  Large hail will be the primary initial threat, and an
   isolated tornado may occur in the zone of vertical vorticity and
   steep low-level lapse rates along the front.  By late evening (near
   and after sunset), the potential for a couple of tornadoes may
   increase near the warm front in north central KS, as the initial
   high-based supercells move far enough eastward to encounter somewhat
   richer low-level moisture and low-level shear strengthens.  

   Upscale growth into clusters is also expected around 03z, and
   convection will spread eastward along the warm front into MO through
   the overnight hours, supported by warm advection on the nose of a 60
   kt low-level jet.  The mode transition will result in a shift to
   more of a damaging wind threat tonight, though isolated large hail
   and a tornado or two may still occur with the stronger embedded
   updrafts/circulations.

   ...Western OK/TX area this afternoon/evening...
   The corridor of richer moisture return will remain well east of the
   southern Plains dryline through this evening.  Deep mixing and a
   narrow zone of ascent along the dryline could support isolated
   thunderstorm development late this afternoon/evening; thus, will
   maintain the MRGL risk area to reflect the highly-conditional threat
   for supercells this evening.

   ..Thompson/Moore.. 05/08/2021

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