SPC AC 300552

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1252 AM CDT Sun Apr 30 2023

   Valid 301200Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE CAROLINAS AND MID ATLANTIC AS WELL AS INTO CENTRAL AND SOUTHERN
   FLORIDA...

   ...SUMMARY...
   Severe thunderstorms will be possible across parts of the Carolinas
   into the Mid Atlantic, and also across parts of central and south
   Florida. Damaging winds and a few tornadoes will be the primary
   hazards, though isolated hail will also be possible.

   ...Synopsis...
   In the mid levels, 00z RAOB data showed an incipient omega block
   developing over the west-central CONUS with a broad cyclone over the
   eastern Great Lakes occupying the eastern node of the block. To the
   south of the closed low, a southern stream shortwave trough and
   accompanying jet streak were observed along the upper Gulf Coast.
   The shortwave and jet streak are forecast to move north across
   Southern and Mid Atlantic Seaboard through the day with an
   accompanying surface cyclone and trailing cold front. As the front
   and low move eastward, strong lift and deep moisture will support
   thunderstorm development ahead of the front from the Carolinas,
   southward across FL, before shifting offshore. By early evening, the
   deepening upper cyclone should absorb the shortwave as the omega
   block becomes established across much of the CONUS, and a second
   cold front crosses the Appalachians.

   ...Carolinas to the southern Mid Atlantic...
   By 12z, the sub-1000mb surface low should be located near the middle
   NC/SC border with the cold front tailing south over the western
   Piedmont. Widespread rain and cloud cover are expected over the
   Carolinas in the wake of previous day's convection. Pockets of
   insolation may support MLCAPE near 1000 J/kg given surface dewpoints
   the mid 60s F. Scattered thunderstorms are expected to form early in
   the morning and persist through midday ahead of the cold front.
   Strong meridional flow will support elongated, but mostly straight
   hodographs. Several bands or clusters of linear storms and a few
   supercells will likely organize with a risk for damaging wind gusts.
   A couple tornadoes will also be possible given enhancement of the
   low-level shear by a 40-50 kt low-level jet.

   As the surface low lifts northeastward through the morning, strong
   southerly low-level flow will quickly veer as the front sweeps
   eastward. Storms will shift northward into the Mid Atlantic by late
   morning and early afternoon. Strong vertical shear will remain in
   place as the shortwave and jet streak lift northward, supporting a
   continued risk for damaging gusts and perhaps a tornado. However,
   much weaker buoyancy is expected with northward extent, owing to
   weaker insolation and the northern limit of deeper surface moisture
   over southern VA with surface dewpoints in the upper 50s to low 60s
   F. Storms should gradually weaken through the late afternoon and
   early evening, as they cross into the cooler and more stable air
   mass. The cold front and surface low should finally move offshore
   early in the evening, ending the severe threat.

   Isolated severe storms may also develop in the lee of the central
   Appalachians across western NC/SC and VA ahead of the second polar
   front moving eastward. Confidence in severe coverage here is much
   lower owing to weaker buoyancy from previous convection and veered
   surface flow. Strong mid-level westerlies may still support the risk
   for a few damaging wind gusts with marginally organized short line
   segments or multicell clusters through the afternoon.

   ...South Florida...
   Along the southern end of the front, moist inland flow is expected
   through the morning hours across portions of South FL. Frontal
   forcing should support scattered to numerous thunderstorms from
   early to mid morning as the front moves southeast. Mid 70s F surface
   dewpoints and modest mid-level lapse rates near 6 C/km will support
   inhibition-free, 1500-2000 J/kg of MLCAPE early in the day. 50-60 kt
   of 500mb flow behind the departing shortwave will linger over the
   southern peninsula, supporting elongated hodographs and sufficient
   mid-level shear for storm organization. Short linear segments and or
   supercell structures may evolve with a risk for damaging gusts and
   isolated hail ahead of the front. A few tornadoes are also possible
   with any sustained supercells. Though low-level shear will be
   strongest early in the period before it gradually weakens through
   the day as low-level flow veers along the front. Storms should
   continue to move east/southeast with a risk for wind and hail
   through the early afternoon. The severe risk should end by late
   afternoon/early evening as storms and the front move completely
   offshore by 20-22z.

   ..Lyons/Kerr.. 04/30/2023

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