SPC AC 210600

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Thu May 21 2020

   Valid 211200Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN AND CENTRAL HIGH PLAINS...

   ...SUMMARY...
   A few severe thunderstorms are expected this afternoon and evening
   in the southern and central High Plains. Other marginally severe
   thunderstorms may occur in the Carolinas and Florida.

   ...Southern and Central High Plains...
   An upper-level trough will move into the Four Corners area today as
   cyclonic southwest mid-level flow remains over the southern and
   central High Plains. At the surface, a low will deepen today across
   the Texas Panhandle as a surface trough sharpens across west Texas.
   To the northeast of the surface low, winds will remain backed to the
   east-southeast in northwest Oklahoma and southwest Kansas. Surface
   dewpoints along this southeast-to-northwest corridor will be in the
   60s F resulting in moderate instability by afternoon. RAP forecast
   soundings increase MLCAPE to near 3000 J/kg along this corridor by
   late afternoon. The forecast wind profile in southwest Kansas has
   veering winds with height below 700 mb with speed shear present in
   the mid-levels. This will likely result in 0-6 km shear values near
   40 kt, which combined with 700-500 mb lapse rates approaching 8.0
   C/km, will be favorable for supercells with large hail. The more
   dominant supercells may be able to produce hailstones greater than 2
   inches in diameter. A tornado or two will also be possible with the
   greatest potential in far southwest Kansas and the eastern Oklahoma
   Panhandle.

   Further to the south across west Texas, a dryline will be present
   along the eastern edge of the Caprock. Surface dewpoints to the east
   of the dryline in the 60s F will contribute to moderate instability
   by afternoon. Low-level convergence is expected to be weak but
   perhaps should be enough for convective initiation of multiple
   cells. The instability combined with steep mid-level lapse rates and
   0-6 km shear of 30 to 40 kt will be sufficient for a severe threat.
   Supercells could form with any cells that can initiate and grow
   upscale. These storms would have potential for large hail. However,
   much of west Texas will be free of convection due to the weak
   low-level convergence. Although some uncertainty still exists
   concerning the spatial distribution of convection, confidence is
   great enough that convective initiation will occur to add a slight
   risk into parts of west Texas.

   ...Carolinas...
   An upper-level low will move slowly north-northeastward today across
   the lower Ohio River Valley. To the east of the upper-level low,
   cyclonic south to southwest mid-level flow will be in place across
   the Carolinas. At the surface, a mesolow is forecast to develop in
   South Carolina with winds to the northeast of the low backed to the
   southeast. In response, a corridor of enhanced low-level moisture
   and instability should be in place by afternoon from eastern South
   Carolina into southern North Carolina. Thunderstorms that form in
   this airmass may have marginally severe wind gusts, especially as
   low-level lapse rates steepen during the early to mid afternoon.

   ...Florida...
   A moist airmass will be in place today across the Florida Peninsula.
   Surface dewpoints from the mid upper 60s F into the lower 70s F
   should result in a pocket of moderate instability across the central
   Florida Peninsula by afternoon. Thunderstorms will develop across
   the eastern Florida Peninsula as a sea breeze boundary moves inland
   from the eastern coast. Marginally severe wind gusts will be
   possible with the stronger multicells during the mid afternoon.

   ..Broyles/Moore.. 05/21/2020

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