SPC AC 201645

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1145 AM CDT Sat Jun 20 2020

   Valid 201630Z - 211200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   DAKOTAS/NEBRASKA AND SOUTHERN PLAINS...

   ...SUMMARY...
   Scattered severe hail and damaging wind will be possible from
   eastern North Dakota to central Nebraska between about 2 to 10 PM
   CDT. Scattered large hail and severe wind gusts are also possible
   across parts of west Texas this afternoon into southern Oklahoma
   tonight.

   ...Dakotas/Nebraska...
   No changes warranted for this region. Scattered thunderstorms are
   still expected to develop by mid-afternoon along a surface trough
   from eastern North Dakota to central South Dakota, and by early
   evening into west-central Nebraska. While surface dew points should
   largely hold in the mid to upper 50s F within a confined plume ahead
   of the trough, relatively cool mid-level temperatures associated
   with a Prairie Provinces to North-Central States shortwave trough
   should foster moderate buoyancy with MLCAPE reaching 1000-2000 J/kg.
   Effective shear of 25-35 kt (generally on the stronger side across
   NE/SD) will support multicell clusters and a few supercells with
   risks for severe hail and wind. The severe threat should trend more
   marginal/isolated this evening.

   ...West-central Kansas...
   While overall forcing for ascent/convergence will remain weak, there
   are some indications that isolated severe thunderstorms could
   develop across the region late this afternoon/early evening.
   Buoyancy/mid-level lapse rates will not be overly strong/steep
   (respectively) by late spring standards, but steep low-level lapse
   rates/moderate buoyancy in the presence of 30-35 kt effective shear
   could support a few supercells/multicells with some severe hail/wind
   potential.

   ...Southern Plains...
   Multiple scenarios/corridors of severe potential are expected across
   the region later today into tonight, although forecast confidence is
   not particularly high in the wake of last night's MCS and related
   outflow/air mass impacts. The relatively highest confidence severe
   potential may be across the Texas South Plains/West Texas Permian
   Basin vicinity and Transpecos. Aided by a moist air mass (reference
   Del Rio 12Z observed sounding), thunderstorm development should
   occur over the higher terrain and near the lee trough/dryline and
   remnant outflow vicinity. A combination of supercells/multicells
   could yield large hail and damaging winds, with the possibility that
   a small cluster or two could evolve this evening.

   Farther north, air mass recovery should gradually occur across far
   north Texas into parts of Oklahoma. Thunderstorms may develop this
   evening as warm advection increases. Convection should tend to
   cluster relatively quickly but large buoyancy and 30-35 kt effective
   shear should support a risk for large hail and severe wind.

   ...Middle/Upper Mississippi Valley...
   Ahead of a weak front, a broad portion of the middle/upper
   Mississippi Valley region will become modestly unstable this
   afternoon. Scattered thunderstorm redevelopment and intensification
   is expected this afternoon across a fairly broad region. Effective
   shear of 20-30 kt will support some semi-organized multicell
   clusters, with an attendant risk of locally damaging wind and
   marginally severe hail.

   ...South Atlantic Coastal Plain...
   As an upper low slides southeast across eastern North Carolina, a
   belt of enhanced mid-level northwesterly winds around 25 kt should
   be centered on the Savannah Valley. Isolated to scattered
   thunderstorms are expected along the sea breeze with a few cells
   capable of locally damaging wind and marginally severe hail.

   ..Guyer/Nauslar.. 06/20/2020

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