LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Sat Apr 29 2023
Valid 291200Z - 301200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN
GEORGIA INTO THE FLORIDA PENINSULA...
...SUMMARY...
Two rounds of strong to severe thunderstorms are expected across
portions of Florida and southern Georgia this afternoon and
overnight tonight with damaging winds, large hail, and a few
tornadoes possible. More isolated severe storms are possible across
parts of Mississippi and Alabama with an attendant damaging
wind/hail threat.
...Synopsis...
An organized, but slowly decaying, MCS is noted moving off the TX
Gulf Coast ahead of an upper-level wave over the southern Plains.
This MCS is forecast to migrate eastward across the Gulf of Mexico
as a convectively augmented MCV along a diffuse baroclinic/buoyancy
gradient noted in recent analyses (and supported by 00 UTC soundings
along the Gulf Coast and maritime observations). This feature should
reach the FL coast by mid-afternoon, well ahead of the slower
upper-level wave. The first round of convection is expected this
afternoon as the MCS/MCV reaches the FL coast, while a second round
of storms is anticipated during the early morning hours Sunday as a
cold front associated with the synoptic wave moves across the FL
Peninsula.
...Florida to southern Georgia...
00 UTC soundings along the FL Peninsula sampled an unstable air mass
featuring MLCAPE values on the order of 1500-2000 J/kg. Little
change is anticipated to the temperature profile through
mid-afternoon, and surface temperatures warming into the low to mid
80s should result in similar buoyancy values by peak heating.
Thunderstorm development will likely be focused along 1) a
diurnally-driven sea-breeze boundary along the eastern FL/southeast
GA coast and 2) along and ahead of the approaching MCS/MCV.
Nearly-straight hodographs featuring nearly 40 knots of effective
bulk shear should support organized discrete cells, including a
couple of supercells, along the east coast with an attendant
large-hail risk. More clustered storm modes associated with the
MCS/MCV across western FL, the FL Panhandle, and southern GA should
primarily pose a damaging-wind threat. This first round of storms
should migrate into the Atlantic during the 00-03 UTC period.
A surface low and attendant cold front (currently pushing across the
TX Coastal Plain) is forecast to meander eastward in tandem with the
upper trough, reaching the western FL coast and parts of southern GA
during the 08-12 UTC period. Low and mid-level wind fields will
strengthen ahead of the front, enlarging low-level hodographs in the
process. Wind magnitudes will likely be dependent on how rapidly the
surface low deepens over the Gulf states during this period, but
most solutions hint at 0-1 km SRH values on the order of 200-250
m2/s2. Fast storm motions off the front should favor semi-discrete
cells with a few supercells possible, and the favorable low-level
hodographs will support a nocturnal tornado threat with more robust
cells.
Despite these factors, the degree of destabilization between the two
rounds of convection is very uncertain. Most hi-res solutions
suggest adequate destabilization along Florida's west coast is
probable, and sporadic maritime observations from the southeastern
Gulf of Mexico (the source region of this recovering air mass) show
high-quality low-level moisture (dewpoints in the mid 70s). However,
the lack of diurnal warming and uncertainties pertaining to prior
convective overturning cast some doubt into this scenario.
...Mississippi into southern Alabama...
While low-level moisture across MS and AL is somewhat meager for
late April (mid 50s dewpoints), the offsetting effects of colder
temperatures aloft associated with the upper-trough and diurnal
warming should support MLCAPE values near 1000 J/kg this afternoon.
Lift associated with the wave combined with elongated hodographs
above 2 km may support a few more intense updrafts with an attendant
hail and damaging wind risk. Confidence in the coverage or longevity
of convection within this regime is low, but the scenario appears to
be depicted well by many 00z CAM solutions in the form of transient
updraft helicity swaths over the region.
..Moore/Kerr.. 04/29/2023
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