SPC AC 061237

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0737 AM CDT Sat Apr 06 2024

   Valid 061300Z - 071200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHWEST
   INTO SOUTHERN NEBRASKA AND CENTRAL AND EASTERN KANSAS...

   ...SUMMARY...
   Severe storms will be possible across parts of the central Plains
   this afternoon and early evening.  Severe gusts and large hail are
   the primary risks with the stronger storms.

   ...Central Plains vicinity...
   Water-vapor imagery this morning shows a powerful negative-tilt mid-
   to upper-level trough over the Four Corners.  This upper disturbance
   will eject east-northeastward into the central Great Plains later
   this afternoon, before evolving into a deep mid-level low near the
   SD/NE border Sunday morning.  An attendant 500-mb speed max will
   move through the base of the trough and overspread the warm sector
   of a deepening cyclone centered over the central High Plains.  A
   cold front will move eastward across KS/OK through the day, with an
   occluded portion of the front expected to extend northwestward from
   north-central KS into western/central NE. 

   Early morning surface analysis indicates the northern periphery of
   50+ deg F surface dewpoints to be confined to OK/TX Red River
   vicinity. Strong low-level moist advection will lead to a narrow but
   adequately moist plume arcing from north TX northward through
   central OK and into central KS/southwestern NE by mid afternoon. 
   Model guidance continues to show surface dewpoints likely remaining
   in the 40s F across most of NE, and only reach the low 50s F
   into parts of central KS---thereby limiting both buoyancy (500 J/kg
   or less of MLCAPE) and the overall magnitude/coverage of the severe
   threat.  Despite the moisture/buoyancy limitations, very strong
   large-scale ascent attendant to the ejecting upper-level trough will
   aid in initial storm development by early afternoon near the
   occluded front across central/western NE, with development possible
   into northern/central KS by mid/late afternoon.  A few low-topped
   supercells are forecast before a transition to more linear modes
   this evening.  

   Storms that can acquire supercell characteristics would yield the
   greatest threat for isolated large hail (1.0-1.5 inch diameter). 
   While the tornado threat may tend to be limited by sparse low-level
   moisture, sufficient low-level shear/SRH could support at least a
   brief tornado threat with any stronger sustained supercell,
   especially in closer proximity to the surface low over southern NE
   and far northern KS.  It appears the predominant risk will be severe
   gusts in the 60-80 mph range owing to steep 0-2 km lapse rates, very
   strong boundary-layer flow, and a more linear mode with time. 

   While the primary severe threat is expected from southwest/central
   NE into central/eastern KS, some threat could spread into eastern NE
   before convection weakens by late evening.  A lower probability for
   thunderstorm development seemingly exists farther south of the
   mid-level speed max across eastern OK and north TX.  A few storms
   will probably develop by early evening along/ahead of the
   dryline/Pacific front.

   ..Smith/Mosier.. 04/06/2024

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