Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1123 AM CDT Sat Mar 25 2023 Valid 251630Z - 261200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR THE UPPER OHIO RIVER VALLEY...SOUTHEAST GEORGIA AND NORTHERN FLORIDA...AND ALABAMA... ...SUMMARY... Strong to severe thunderstorms capable of damaging winds, large hail, and brief tornadoes are possible across parts of the upper Ohio River Valley and southeast Georgia and northern Florida this afternoon. Another round of strong to severe storms is expected during the early morning Sunday hours across southern AL.
...Synopsis...
Latest water-vapor imagery shows a compact, well-organized upper low over the IL/IN region with a pronounced slot of dry air pushing north ahead of the main vorticity maximum. At the surface, a 994 mb surface low over southern lower MI is expected to gradually shift east/northeast towards the Northeast over the next 12-24 hours in tandem with the upper wave. Strong flow and ascent associated with this feature is expected to overspread the upper OH river valley and lower Great Lakes region, which will support the potential for strong to severe thunderstorms through the late afternoon. Across the Southeast, ongoing convection along a residual outflow boundary is expected to persist into the mid/late afternoon and intensify to severe limits. A late-night round of strong to severe thunderstorms is expected during the early morning hours Sundays across parts of MS/AL as the outflow boundary advances north as an effective warm front tonight.
...Upper Ohio River Valley... Considerable clearing is ongoing across parts of southern OH into far southwest PA as the aforementioned dry slot advances northward. This clearing has allowed temperatures to warm into the low to mid 60s ahead of an approaching cold front, which, as of 15:45 UTC, is slightly warmer than most 12 UTC guidance. Consequently, low-level lapse rates have already increased to around 7 C/km where warming has been maximized. The combination of warming surface temperatures, mid to upper 50s dewpoints, and cool temperatures aloft will support increasing buoyancy through the mid-afternoon hours. Shallow convection evident in visible imagery along the front across western OH is expected to intensify as it moves into the destabilizing air mass. Strong kinematic fields sampled by morning soundings and recent VWP observations will be favorable for organized convection, and the steep low-level lapse rates will allow for efficient mixing of 50+ knot boundary layer winds to the surface. As a result, damaging winds appear likely across eastern OH to western PA and portions of western NY, though a few instances of severe hail and perhaps a brief tornado are plausible.
...Southeast Georgia and northern Florida... GOES IR imagery has shown a slow intensification of ongoing convection across portions of central/southern GA. Although this region will become increasingly displaced from synoptic ascent and stronger mid-level flow through the day, regional VWPs show sufficient deep-layer shear for organized convection through peak daytime heating. Furthermore, quality low-level moisture (sampled by the 12 UTC TLH and JAX soundings) will migrate northeastward ahead of the convection, allowing for MLCAPE values to increase to near 2000 J/kg. As a result, the recent intensification trend will likely continue through the day and regionally augment the potential for damaging winds and hail.
...Alabama... The residual outflow boundary draped across the Southeast from prior convection over the past 24 hours is expected to gradually lift to the north through the day, eventually becoming draped from southeast LA into southern MS and central AL by late tonight. A weak mid-level perturbation is expected to move into the southern Plains/lower MS River Valley during the 00-12 UTC period, which will help strengthen southerly 850 mb flow and bolster isentropic ascent over the boundary. Despite some nocturnal cooling, profiles are expected to be weakly capped with MLCAPE values near 1000-2000 J/kg during the overnight period. Elongated hodographs featuring around 50 knots of effective shear should support organized cells, including splitting supercells, that will pose a severe wind/hail risk (though storm motions along the boundary may limit individual cell longevity and promote upscale growth into clusters). Timing of this convection remains uncertain with recent CAMs showing spread in the onset of convective initiation, but the probability of CI prior to 12 UTC has increased sufficiently to introduce higher risk probabilities. ..Moore/Hart.. 03/25/2023