Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Feb 11 2023 12:54:24 ACUS01 KWNS 111254 SWODY1 SPC AC 111252 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0652 AM CST Sat Feb 11 2023 Valid 111300Z - 121200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN FLORIDA PANHANDLE ACROSS NORTHERN FLORIDA... ....SUMMARY... Damaging thunderstorm winds and a couple of tornadoes are possible from the eastern Florida Panhandle across northern Florida this afternoon and evening. ....Synopsis... In mid/upper levels, a progressive, split-flow pattern will persist through the period, with the splitting features being two similarly sized cyclones somewhat detached from the prevailing northern stream. The first -- initially centered over east TX -- is forecast to move across the southeastern CONUS through the period, with its center reaching southern MS by 00Z and then turning northeastward toward northwestern GA by 12Z tomorrow. Associated height falls already are underway over the northern Gulf and most of the mainland Southeast, and will spread eastward to the southern Atlantic Coast and southeastward over the FL Peninsula. Upstream synoptic-scale ridging aloft -- now over the Rockies -- will deamplify slightly as it moves eastward across the Plains States, ahead of both a northern-stream perturbation digging southeastward from northwestern BC across the western Canadian Prairie Provinces, and the other cyclone -- centered over northwestern CA at present. The latter's associated 500-mb low will move south-southeastward along the north-central CA Coast today. The low then will move obliquely offshore from southern CA by the end of the period, but with associated cyclonic/difluent flow spreading across much of northwestern MX and the desert Southwest. At the surface, a frontal-wave low was evident in satellite imagery over the northeastern Gulf, roughly south of PNS and west of PIE, with warm front drawn northeastward to just offshore AAF, then eastward over the northern FL Peninsula. A cold front extended south-southwest of the low to the south-central Gulf. The low is forecast to curl northward over the eastern FL Panhandle and into extreme southwestern GA or southeastern AL by 00Z, with warm front eastward across extreme southern GA, and cold front arching across Apalachee Bay, parts of northwestern FL, just off the west-central FL coastline, to the east-central Gulf. The initial low should wrap back and occlude over AL tonight, then move eastward toward western GA. Meanwhile the triple point should slide eastward over southeastern GA, then northeastward near the Atlantic Coast, accompanied by a newer low that should reach the MYR area by 12Z. At that time, the cold front will have passed offshore from all but perhaps the immediate coastal areas of south FL along the PBI/FLL/ MIA/HST urban corridor. ....FL Panhandle/North FL and vicinity... Scattered to numerous showers and widely scattered to scattered thunderstorms are expected to develop near the cold front over the northeastern Gulf today, moving inland across the eastern Panhandle and coastal bend regions of FL. Meanwhile, additional, mid/late- afternoon convection may form farther east over the northern FL, focused in a weak-MLCINH environment along residual boundaries from morning clouds/precip. Wherever sustained/mature storms can access surface-based inflow, supercells and/or small bowing/LEWP segments are possible, offering damaging gusts and a threat of a couple tornadoes. Considerable mesoscale uncertainty still exists regarding the location and extent of diurnal destabilization and remnant boundaries behind a plume of precip now moving out of northern FL, as well as a trailing swath of broken multilayered clouds extending back across the Gulf. This will influence convective coverage, and strongly regulate potential for sustained/discrete supercells. As such, no substantial changes are warranted to the previous outlook, which remains rather conditional. Mass response to the approaching cyclone aloft, with the deepening surface low, should lead to low-level warm advection that can destabilize some areas in the northern part of the outlook now still under the influence of earlier outflow/precip -- though favorable destabilization all the way north to the warm front is quite uncertain. The low's inland penetration also should outrun the surface-based warm sector inland into AL/GA. Sufficient diabatic heating and warm advection should support 500-1000 J/kg preconvective/prefrontal MLCAPE across much, if not all of the outlook area. As the day progresses, strengthening deep-layer flow will lead to greater vertical shear, with forecast soundings indicating 45-55-kt effective-shear magnitudes common across northern FL and the FL/GA line region by around 21Z. Long, somewhat curved hodographs with 200-300 J/kg effective SRH (most of it in the lowest 1/2 to 1 km) are possible, suggesting tornado potential with any sustained/ discrete supercells that can form. As the front proceeds eastward toward the northwestern/west-central peninsular coast early this evening, associated thunderstorms also may move ashore. Greater buoyancy is expected, with 1000-1500 J/kg MLCAPE possible, but weaker deep-layer lift and low-level shear. As such, severe potential becomes more marginal with southward extent. ....Coastal Carolinas overnight... As the triple-point low moves past the CHS area, surface-based buoyancy (which will be greatest over offshore Atlantic waters) may brush the immediate coastline from there northeastward toward ILM in the 09-12Z time frame. The buoyancy/shear parameter space favors supercells in forecast soundings not far offshore. At this time, too much uncertainty remains to introduce an unconditional outlook area in that corridor that would link to the early day-2 area for the southern Outer Banks, but only very minor northward shifts in progs and/or mesobeta-scale trends would be needed to introduce a threat. This scenario will be monitored closely throughout the remainder of the period. ...Edwards.. 02/11/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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