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
