Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 22 2023 12:50:59 ACUS01 KWNS 221250 SWODY1 SPC AC 221249 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0749 AM CDT Sat Apr 22 2023 Valid 221300Z - 231200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN PARTS OF THE CAROLINAS...MID-ATLANTIC AND SOUTH TEXAS... ....SUMMARY... Severe thunderstorms are possible today over parts of the Carolinas into the Mid-Atlantic region, and this afternoon and evening over portions of south Texas. ....Synopsis... In mid/upper levels, moisture-channel imagery reveals an elongated cyclone with two primary centers: one over far northwestern ON, the other over the western Lake Superior region. A series of shortwave troughs is embedded in the extensive swath of associated cyclonic flow from the Rockies to the Atlantic Coast, with the leading perturbation now evident from the southwestern Lower MI area southward to middle TN. The southern of the two lows should shift/ redevelop southeastward toward MKG by 00Z, while the basal shortwave trough pivots east-northeastward, reaching the upper Ohio Valley, VA Blue Ridge area, and the NC/TN border. By 12Z tomorrow, the southern mid/upper low will weaken and eject over the neck of ON, while the primary cyclone center aloft takes over just north of the MN/ON border. The lead shortwave trough should stretch and weaken over NY/NJ, as an upstream perturbation follows it across the upper Ohio Valley. At the surface, 11Z analysis showed a triple-point low near PIT, with warm front east-southeastward over southern NJ, and cold front across WV, southwestern VA, higher terrain of western NC/SC, to central GA, the FL Panhandle, and north-central Gulf, becoming quasistationary to warm across the northwest Gulf to near BRO. A separate frontal zone was drawn from the Arklatex region across north-central TX, through a low near MAF. The Northeast low should move northward over southwestern QC by 00Z, with cold front across central NY, eastern parts of PA/MD/VA/NC/SC, near the GA Coast, and across northern FL. Farther southwest, the TX low is expected to meander to the Edwards Plateau through 00Z, as the reinforcing frontal zone shifts southward slowly over north TX, the northern Hill Country, and the Permian Basin. The western limb of the gulf front will move diffusely northward over deep south TX toward the southern part of the Balcones Escarpment today. ....Carolinas to Mid-Atlantic... An ongoing, near-frontal convective band has crossed portions of AL/GA and the western Carolinas to southwestern VA during the prior overnight period into early this morning, remaining largely elevated and producing no known severe (50+ kt) gusts. However, as the accompanying swath of low-level lift continues to shift eastward/ northeastward, it will encounter progressively more-favorable boundary layer through the remainder of the morning and into the afternoon, and gradually become better organized, with increasing potential for damaging to severe gusts and a few tornadoes. See SPC mesoscale discussion 591 for near-term guidance in parts of NC/VA. With the southern part of this activity getting ahead of the front, and continued moist/warm advection expected from the Atlantic, additional rounds of thunderstorms may occur ahead of or behind the initial band over parts of the Carolinas. Foregoing destabilization already is underway in the form of theta-e advection extending at least a marginally buoyant, surface-based effective-inflow layer into much of eastern SC and south-central NC. This process will spread northward through the eastern Carolinas and Mid-Atlantic into the afternoon, with associated destabilization augmented by erratically paced diurnal heating under cloud cover. As this occurs, a northward-narrowing corridor of preconvective MLCAPE should develop, ranging from around 500 J/kg or less over southern NY and eastern PA to 1000-1500 J/kg in the eastern Carolinas. Deep-shear vectors will be modest (e.g., effective-shear magnitudes of 25-35 kt being common) and oriented nearly parallel to the convective band, though some veering/strengthening of low-level flow with height will enlarge hodographs slightly over parts of VA/NC. Embedded supercells/mesovortices and bow/LEWP formations will augment wind, hail and perhaps tornado threat locally. Severe potential should diminish and shift offshore after about 00Z. ....South TX... Isolated to widely scattered thunderstorm development is possible by mid/late afternoon over two main areas -- each potentially prone to large/damaging hail and strong-severe gusts. A tornado is possible as well, mode dependent on storm-scale processes. The areas of convection: 1. A southward-shifting frontal zone near the surface low, where low-level convergence will be maximized in and above the boundary layer, and 2. Higher terrain (Serranias del Burro) of northern Coahuila, where enough easterly component to near-surface flow will exist to provide orographic lift, augmenting the strong diurnal heating of the higher terrain in supporting convective initiation. Activity in both areas may persist into the evening to early overnight hours before weakening. The near-frontal convection should be the primary concern over the outlook area, with enough low-level shear (effective SRH around 150-300 J/kg) and deep shear (effective-shear magnitudes 50-70 kt) to support supercells. With surface dewpoints only in the 50s to low 60s F over much of the projected inflow region of this activity, buoyancy will be somewhat limited at first, especially for this area and time of year, with MLCAPE in the 500-1500 J/kg range over northern parts of the outlook area. However, moisture and low-level instability will increase with southward extent over south TX, so that 2000-3000 J/kg MLCAPE will be possible south of the escarpment and near the Rio Grande in the DRT-LRD corridor. This will be east of any Mexican development and south of any upscale growth of Hill Country/Edwards Plateau storms that can survive that far south. In this flow regime, right-moving supercells from MX likely will stay southwest of the Rio Grande, but any left splits or outflow- driven/upscale clustering may cross into TX with associated hail/ wind potential. Since this is a more isolated and uncertain threat than the development farther north, unconditional probabilities are kept marginal -- acknowledging potential for significant hail under optimal circumstances (a discrete supercell in this favorable CAPE/shear parameter space). ...Edwards/Jewell.. 04/22/2023 $$ = = = 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) .