Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 22 2022 13:00:45 ACUS01 KWNS 221300 SWODY1 SPC AC 221259 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0659 AM CST Thu Dec 22 2022 Valid 221300Z - 231200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE EASTERN CAROLINAS AND PARTS OF THE FLORIDA PENINSULA... ....SUMMARY... Isolated, marginally severe thunderstorms are possible today over the eastern Carolinas and this evening into tonight across parts of the Florida Peninsula. ....Synopsis... The mid/upper level pattern over the CONUS will amplify through the period, related largely to a broad, deepening cyclone now centered over northern ND. The associated 500-mb low should pivot roughly eastward to northern MN today, while a strong, basal shortwave trough amplifies across the central Plains. By 00Z, the latter feature should reach the Ozarks, then pivot northeastward up the Ohio Valley. That will occur in the left-exit region of an intensifying speed max, with core winds near 150 kt at 500 mb and 160-170 kt at 250 mb by 12Z, around the broader cyclone's southern semicircle. Ahead of that process, a subtle, positively tilted, southern-stream shortwave trough was apparent in moisture-channel imagery from WV southwestward across AL. This trough's southern vorticity lobe over AL is expected to move east-northeastward across the Carolinas this afternoon, amidst large-scale height falls related to the deepening synoptic cyclone. Still farther south: a weak, elongated vorticity banner initially over the western/central Gulf should move eastward across FL overnight. The 11Z surface analysis depicted a low over northeastern WI, with seasonably intense arctic cold front extending across northwestern IL, central MO, south-central OK, the TX South Plains, and east- central/northeastern NM. A frontal-wave low was analyzed along an older baroclinic zone over the Atlantic, just S of CHS, with warm front east-northeastward across SC/southern NC shelf waters, then eastward over the open Atlantic. A trailing cold-frontal segment extended south-southeastward to near MIA then west-northwestward over the northeastern Gulf to a weak low well south of PNS. By 00Z, the northern low will be occluding/filling over Lake Superior, with cold front surging across central KY, middle TN, MS, southern LA, and across TX coastal/shelf waters to near BRO. Meanwhile a second low should organize over the eastern IN/western OH area, then eject northward to Lake Huron by 12Z tomorrow as the center of a rapidly deepening surface cyclone. By then, the arctic cold front should reach the coastal Mid-Atlantic and NC Outer Banks, then arc across Atlantic waters to central FL and the central/southwestern Gulf. ....Eastern Carolinas... Widely scattered to scattered thunderstorms should develop the next few hours in a band extending roughly north-south near the surface cold front now over the region. This activity then should move northeastward across the outlook area, offering isolated damaging gusts. Marginally severe hail also is possible, given steep mid/ upper-level lapse rates and supercell-favorable wind profiles; a 2D hail model and several sounding analogs indicate 1-1.5-inch hail possible. A tornado cannot be ruled out, given the low LCL and presence of sufficient shear for supercells. As the leading southern-stream perturbation approaches, the Atlantic low should move inland in the next few hours, then north- northeastward across the eastern Carolinas. The warm front, and a partly modified marine/warm sector following it across cool near- coastal shelf waters, will shift somewhat more slowly northward. This should spread higher-theta-e, surface-based effective-inflow parcels somewhat inland in support of strong-severe convective potential. Forecast soundings suggest temperatures and dewpoints around 65 and 63 F respectively may support minimal CINH and MLCAPE around 500 J/kg, with higher values near the northeastern NC and southern NC coastline potentially fostering a brief/narrow wedge of better-modified warm-sector air with MLCAPE near 1000 J/kg. Along and south of the warm front, effective-shear magnitudes of about 30-40 kt are expected, along with enough backing of near-surface flow to support 150-200 J/kg effective SRH. Convective potential should diminish rapidly from late afternoon onward as the mid/upper perturbation and eastern cold front pass, and the combination of cold advection and diabatic/nocturnal stabilization occur. ....FL... Widely scattered thunderstorms should develop by late this afternoon along and south of a remnant frontal segment over the Gulf, and ahead of the southernmost shortwave perturbation. Activity then should move across central/southern parts of the peninsula, offering an isolated severe-gust threat, and perhaps a brief tornado potential, from late afternoon into tonight. Some convection may become supercellular for at least brief interludes. At the southern periphery of the broader-scale height falls, increasing midlevel winds across the northeastern Gulf, then FL, will enhance deep shear over the region -- especially near the West Coast of FL where relatively backed surface winds may persist into the evening. Effective-shear magnitudes of 45-60 kt are present in some forecast soundings. Though low-level flow will not be particularly strong, enough hodograph curvature will exist to support 150-200 J/kg effective SRH. Meanwhile, gradual increases in theta-e are expected over the southern/central peninsula as the remnant front becomes somewhat more diffuse, supporting inland development of around 1000 J/kg MLCAPE. Buoyancy then may increase further this evening -- especially over west-central/southwestern FL -- as veering low-level winds herald moist advection off the Gulf (though the veering also reduces shear and lift somewhat). Convective coverage is uncertain, but greater confidence in sustained/multiple supercells may support an upgrade in a succeeding outlook, given the favorable wind profiles for a few hours. ...Edwards/Kerr.. 12/22/2022 $$ = = = 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) .