Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 31 2022 12:56:46 ACUS01 KWNS 311256 SWODY1 SPC AC 311255 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0655 AM CST Sat Dec 31 2022 Valid 311300Z - 011200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHEAST TODAY... ....SUMMARY... Isolated strong to severe thunderstorms are possible across parts of the Southeast today. ....Synopsis... A mid/upper-level synoptic-scale trough -- initially over the central CONUS -- will move eastward and weaken through the period. This will occur as a basal shortwave trough -- initially evident in moisture-channel imagery over portions of AR/LA -- moves east- northeastward and deamplifies, reaching GA and easternmost TN by 00Z, then moving offshore NC around 06Z. Well upstream, a strong, highly progressive, positively tilted shortwave trough was noted over the northeastern Pacific, west of CA, roughly between 132W-136W. Positively charged lightning consistently has been detected in the cold-core convective region of this perturbation since at least yesterday afternoon, indicating strong midlevel destabilization/ascent to support thunderstorms over cool waters. This trough will amplify further and become nearly neutrally tilted as it crosses all of northern and much of central/ southern CA between 00-12Z tonight. Associated large-scale ascent and moisture will support general thunder potential over parts of the Sierra and vicinity. At the surface, 11Z analysis showed a weakening cold front extending from a low over northwestern OH southwestward across western parts of KY/TN to southwestern LA and the northwestern Gulf. Substantial convective potential today should remain well removed to the southeast of this boundary. ....FL Panhandle to SC Lowcountry... Isolated to widely scattered thunderstorms are possible this afternoon in a prefrontal, southwest/northeast-oriented band of weakly forced convection that should move east-northeastward over the outlook area. A marginal and conditional threat exists for a severe gust or tornado. Though the mid/upper-level shortwave trough will be deamplifying as it approaches, location-relative increases will occur in large-scale ascent, winds aloft and deep-layer shear. 40-50-kt effective-shear magnitudes, with relatively straight hodographs, are expected over the outlook area, suggesting some supercell potential, though weakness of both buoyancy and forcing (below) cast uncertainty on the size and longevity of any storm-scale rotation. CAM UH progs reasonably are consistent with this conceptual model as well, showing only short-lived, weak streaks. Low-level mass response will be muted, with modest increases in (but veering of) 850-mb flow, while surface winds remain weak and gradually veer with time. With regard to low-level lift, that veering tendency will reduce convergence with time. Still, as an offsetting factor, weak ambient MLCINH is expected this afternoon, as the boundary layer undergoes subtle diurnal heating (with considerable cloud cover lingering) and theta-e advection behind the morning precip plume. Though midlevel lapse rates will be modest, enough theta-e should characterize the boundary layer to support around 500 J/kg MLCAPE, locally/briefly approaching 1000 J/kg where any cloud breaks can foster some sustained insolation. ....West-central FL... Episodes of thunderstorms should occur offshore today, including an ongoing convective west of the west-central FL coastline. As this activity moves east, it will encounter an environment of at least marginally favorable low/level and deep shear, but less-favorable thermodynamic profiles. Weak low/middle-level lapse rates and buoyancy, sampled by the 12Z TBW sounding. Diabatic heating should steepen overland lapse rates; however, the shallow moist layer in that sounding suggests enough mixing where heating does weaken MLCINH to keep CAPE from getting large. Also, large-scale support may peak before activity reaches the coast, as the shortwave trough to the northwest continues to deamplify. While strong convection may reach the coast before dissipating, the severe threat still appears too conditional/isolated to introduce an area. However this scenario will be monitored through the day for shorter-fused mesobeta-scale trends (such as near-surface veering not currently forecast that may increase moist-layer depth and potential inland convective survival). ...Edwards/Broyles.. 12/31/2022 $$ = = = 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) .