SPC AC 111620

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1120 AM CDT Mon Apr 11 2022

   Valid 111630Z - 121200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATER THIS
   AFTERNOON INTO EARLY TONIGHT FROM EASTERN OK INTO AR...

   ...SUMMARY...
   Isolated to scattered severe thunderstorms are expected later this
   afternoon into early tonight from parts of northeast Texas to the
   Ozarks and Mid-South, with the greatest threat expected over parts
   of far eastern Oklahoma and Arkansas. Very large hail, damaging
   winds, and a strong tornado or two all appear possible.

   ...AR to southeast OK/north TX this afternoon into early tonight...
   Broadly cyclonic flow aloft will persist over the Plains and western
   CONUS, as a lead shortwave trough ejects east-northeastward over
   Lake Superior, and an upstream trough will amplify toward the Great
   Basin.  An outflow boundary across AR and a surface front across
   east central and southeast OK have stalled and these boundaries will
   provide a focus for additional thunderstorm development later this
   afternoon into this evening, as a subtle mid-upper speed max
   progresses east-northeastward from the TX Panhandle.  Late in the
   period, the front will begin to move northward as a warm front
   across OK, in response to strong lee cyclogenesis across the central
   High Plains (downstream from the Great Basin midlevel trough).

   Boundary-layer dewpoints in the mid-upper 60s continue to spread
   northward across TX/LA toward southeast OK and AR, to the south of
   the front and the outflow boundary across northern AR.  Clouds will
   tend to slow surface heating in AR where the moist layer is
   relatively deep, but convective inhibition is not as strong compared
   to areas farther southwest in TX, based on the very warm elevated
   mixed layer noted in regional 12z soundings with convective
   temperatures at or above 90 F.  However, surface heating will be
   stronger from southeast OK into northeast and north central TX where
   cloud breaks will be more pervasive.  Though forcing for ascent and
   the prospects for surface-based storm development are uncertain
   across north TX along the front and dryline, storm development is
   more probable by mid-late afternoon along the front/outflow along
   the northeast edge of the stronger surface heating/deeper mixing in
   southeast OK.  Any storms that form along or just south of the
   front/outflow from southeast OK into AR will likely become
   supercells, given MLCAPE of 2000-3000 J/kg and effective bulk shear
   near 50 kt.

   The large buoyancy, northeast extent of the midlevel lapse rates
   near or above 8 C/km, and supercell wind profiles will support the
   threat for isolated very large hail (potentially near the size of
   baseballs).  Low-level moisture and hodograph length/clockwise
   curvature suggest that tornadoes will be possible with any
   persistent supercells, including a strong tornado or two. 
   Otherwise, storms may persist into the early overnight hours and
   evolve into a cluster or two while spreading eastward across AR,
   before weakening late tonight as the subtle midlevel trough passes
   and background height rises commence over AR.

   ..Thompson/Broyles.. 04/11/2022

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