Administrators NorthGeorgiaWX Posted December 10, 2023 Administrators Share Posted December 10, 2023 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0654 AM CST Sun Dec 10 2023 Valid 101300Z - 111200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE EASTERN CAROLINAS AND SOUTHEASTERN VIRGINIA...AND NEAR THE NORTHEASTERN GULF COAST... ...SUMMARY... Damaging gusts and a few tornadoes are possible mainly over portions of the eastern Carolinas and southeastern Virginia, and the next few hours near the northeastern Gulf Coast. ...Synopsis... In mid/upper levels, high-amplitude synoptic troughing will shift eastward across the eastern CONUS through the period. This will be influenced substantially by a strong, basal perturbation apparent in moisture-channel imagery from southern IL across AR to south-central TX. This feature should assume a less-positive tilt through the day as it pivots eastward, reaching from eastern KY across AL and the western FL Panhandle by 00Z. Thereafter, the shortwave trough will eject northeastward, become more negatively tilted, and after 06Z, weaken substantially -- reaching eastern VA by 12Z tomorrow. At the surface, 11Z analysis showed a cold front from western PA through WV, near TRI, then across eastern/southern AL to the central Gulf. The front should proceed eastward across the central/southern Appalachians today. By 00Z, an elongated area of low pressure (and perhaps one or more discrete, weak lows) should develop along the front, expected to extend from northern New England to southeastern PA, then approximately down the Piedmont into southern GA, to the eastern Gulf. By 12Z tomorrow, a deepening low should consolidate on the front over or near RI, with the boundary extending across Atlantic waters to the FL Keys vicinity. ...Southeast CONUS... A broken band of thunderstorms may continue to pose a threat for a tornado or two and damaging gusts for a few hours, as it shifts eastward through the FL Panhandle and southwestern GA, toward a region of more-stable boundary-layer air over and north of Apalachee Bay. The TLH sounding at 12Z sampled the eastern rim of the moist-unstable low/middle-level profiles well, atop a shallow/stable near-surface layer that may modify somewhat more favorably before the convection moves through the area. Effective SRH in the 150-200 J/kg range was noted, consistent with recent VWP there, and at Eglin AFB before flow veered. For near-term concerns, refer to the remainder of tornado watch 719 and associated mesoscale discussions. A relative minimum in severe probabilities (though not zero) is expected over portions of GA into western SC, where only partly modified, overland trajectories from FL and GA will render inflow- layer instability weak and marginal, at best. However, as the zone of strongest deep-layer ascent shifts eastward today, it will encounter a boundary layer destabilizing from both cloud-muted overland/diabatic heating and low-level theta-e advection off the Atlantic. This will ramp up wind and tornado probabilities again, as thunderstorms reorganize and intensify -- potentially in two episodes: 1. A zone of strengthening low-level convergence preceding the original convective band over easternmost SC, eastern NC and parts of southeastern VA, with activity forming in the warm sector over water and land and moving north-northeastward; 2. The initial main band of lift/convection reaching the same area late afternoon into this evening. In the destabilizing plume, surface dewpoints (already in the low 60s F) should increase to the mid/upper 60s by afternoon as the over-water airmass continues to modify favorably. Low/middle-level lapse rates will be modest but sufficient to support MLCAPE in the 500-1000 J/kg range, in an environment of strengthening deep shear and somewhat enlarged low-level hodographs. A few supercells and small bows will be possible with the warm-sector convection, amidst weak forcing but also weak CINH. The main band of convection may contain embedded supercells and/or LEWP/bowing circulations. Surface-based buoyancy will decrease northward and narrow in lateral extent over the Chesapeake Bay/eastern VA/MD region, but with some severe still possible. Farther south across FL, a line of thunderstorms ahead of the front will offer isolated damaging-wind potential as it crosses from the Gulf into parts of western/northern FL, with some preconvective buoyancy maintained by veering winds off the Gulf. However, that veering will reduce vertical shear and convergence with time this evening, as instability weakens nocturnally, reducing severe potential eastward and southward over the peninsula. ..Edwards/Gleason.. 12/10/2023 Read more View the full article Quote Link to comment Share on other sites More sharing options...
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