Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Dec 20 2022 12:58:29 ACUS01 KWNS 201258 SWODY1 SPC AC 201256 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0656 AM CST Tue Dec 20 2022 Valid 201300Z - 211200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE FLORIDA KEYS AND COASTAL EVERGLADES... ....SUMMARY... Multiple thunderstorm episodes may affect the Florida Keys and coastal Everglades through the period, with isolated damaging to severe gusts possible in the most intense cells. ....Synopsis... The mid/upper-tropospheric pattern begins the period nearly zonal across the CONUS -- perturbed mainly by two shortwaves: one in the northern stream and the other in the southern. The former is located over coastal BC, southwest of a weak/elongated cyclone centered over AB. Merging and amplification of the combined features will lead to the major cyclone forecast to affect the northern CONUS in the next few days. Meanwhile, the more directly influential southern-stream perturbation is evident in moisture-channel imagery over portions of AR, northwestern LA, east and south TX, and northern Coahuila. This feature should maintain positive tilt as it moves eastward over the Gulf Coast and northern Gulf, extending southwestward from southern AL by 00Z and crossing northern/central FL overnight. The associated surface low was analyzed at 11Z south of the Louisiana Coast, with cold front arching southeast through southwest of the low over the west-central Gulf, and warm front east- southeastward to the western Straits between the lower FL Keys and Cuba. The warm front should move slowly northward through the Keys today, perhaps reaching parts of the coastal Everglades of mainland FL. By 12Z tomorrow, the western segment of the warm front will bend to a more northwest/southeast alignment just west of the central/southwestern FL coastline, as the low moves eastward to a position in the northeastern Gulf roughly west of PIE and south of AAF. Northeast of the warm front, a surface trough and weakly frontogenetic confluence zone should form across south-central FL (roughly between FMY-SUA after 06Z, connected to a newer low forming over the Atlantic well east of JAX. ....Southwestern FL and Keys... Multiple episodes of thunderstorms are possible across parts of south Fl and the Keys through the period, with the greatest potential for surface-based, strong to isolated severe convection being over the Keys and perhaps coastal Everglades region. While the outlook remains nearly as conditional as described before, confidence has increased enough in the threat for a marginally severe gust or two to introduce such a probability to this area. The complex surface pattern described above may be made more so by mesoscale precip/convective and marine influences. A strand of convection along the warm front, with widely scattered embedded thunderstorms, already is evident south and southwest of the Keys, and is expected to pivot northeastward into at least the lower/ middle and perhaps upper Keys today. An MCS is apparent over the central Gulf well south of MOB, near the surface low/front, maintained by a combination of favorable large-scale lift/ destabilization ahead of the mid/upper trough, low-level convergence, and favorable low-level theta-e in the well-modified marine layer. This activity, or succeeding convection in the same UVV plume, may reach the outlook area this evening into tonight, encountering a favorable air mass south of the warm front and south of an area of cooler shelf-water sea-surface temperatures farther north up the southwest FL coast. The boundary layer along and south of the front, and away from outflows, will be characterized by surface dewpoints commonly in the 70s F, offsetting modest mid/upper-level lapse rates (especially stable layers between 600-750 mb) enough to support MLCAPE in the 500-1500 J/kg range. The easterly components to boundary-layer flow will help to maintain elongated hodographs and favorable deep shear (35-45-kt effective-shear vectors), though hodograph size will remain small due to weak low-level speeds. Flow ahead of the MCS should veer to a more-southerly component with time this afternoon into evening in isallobaric response to the motion of the Gulf low, but still may maintain supportive storm-relative winds ahead of the MCS. Air-mass recovery farther northeast into mainland southern/ central FL is more improbable, due to clouds/precip and likely upstream near-surface trajectories through more-stable air. ...Edwards/Kerr.. 12/20/2022 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .