SPC AC 291935

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0235 PM CDT Sun Apr 29 2018

   Valid 292000Z - 301200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE HIGH PLAINS REGION...

   ...SUMMARY...
   Widely scattered storms capable of isolated severe wind and hail
   remain likely across parts of the northern and southern High Plains
   this afternoon and evening.

   ...Discussion...
   Very minor adjustments to thunder lines are being made in a few
   areas at this time, however overall reasoning and areal depictions
   from the prior outlook appear to remain reflective of expected
   convective evolution the remainder of the period.

   ..Goss.. 04/29/2018

   .PREV DISCUSSION... /ISSUED 1127 AM CDT Sun Apr 29 2018/

   ...Northern High Plains...
   A minor mid/upper-level speed max and associated vorticity center
   over the eastern Great Basin this morning will eject northeast
   across WY by this evening. Isolated to scattered thunderstorm
   development is expected by mid afternoon across northern WY and
   southeast MT, to the west of the primary lee cyclone near the
   MT/SD/WY border area. Morning guidance suggests mean mixing ratios
   will reach 7-8 g/kg by late afternoon, however this magnitude of
   low-level moisture was confined to the southern Great Plains per 12Z
   soundings. As such, MLCAPE will probably be more limited than in
   model guidance with values expected to remain below 1000 J/kg. 30-40
   kt effective shear should support a couple high-based supercells
   which will be capable of producing isolated large hail. However,
   given the anticipated deep mixed thermodynamic profiles,
   outflow-dominated storms should tend to coalesce into a couple
   northeast moving clusters with isolated severe wind gusts being the
   primary threat in the early evening.

   ...Southern High Plains...
   Afternoon heating/mixing will likely limit boundary-layer dewpoints
   to the 40s across much of the region with lower 50s in the Trans
   Pecos, sufficient for MLCAPE of 500-1000 J/kg north to 1000-1500
   J/kg south. Scattered high-based thunderstorms are expected to form
   by mid afternoon along the lee trough, where inverted-v
   thermodynamic profiles will favor strong outflow winds. Deep-layer
   vertical shear will be on the fringe for organized/supercell storms
   (around 30 kt), though midlevel lapse rates will be sufficiently
   steep for marginally severe hail. The storms may evolve into loosely
   organized clusters/line segments via outflow interactions, but
   storms should weaken quickly after sunset as convective inhibition
   increases and buoyancy decreases with eastward extent.

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