Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Thu Oct 12 2023 08:20:00 ACUS01 KWNS 121251 SWODY1 SPC AC 121250 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Thu Oct 12 2023 Valid 121300Z - 131200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF NORTHERN/CENTRAL FLORIDA. AND OVER PARTS OF THE CENTRAL PLAINS... ....SUMMARY... Large hail, damaging gusts, and a tornado or two are possible today over parts of the central Plains. A few tornadoes and damaging gusts still may occur through midday over portions of northern/central Florida. ....Synopsis... The mid/upper-level pattern is dominated by a temporary Rex configuration over central/western North America, with a quasistationary anticyclone over north-central Canada, and a pronounced, synoptic-scale cyclone over the central/northern Rockies and eastern Great Basin. An omega pattern will redevelop by late in the period, as the western cyclone shifts eastward across the central Plains, while weakening somewhat. The associated 500-mb low should be near EAR by 00Z, moving slower overnight to a position over eastern NE. By that time, the accompanying trough should be positively tilted, extending southwestward to the TX Panhandle, with most (if not all) midlevel DCVA behind the surface cold front described below. For this outlook, surface synopses will appear in their geographic sections. ....FL... A few tornadoes and severe gusts remain possible across the outlook area today. For near-term guidance, see tornado watch 708 and related mesoscale discussions. A slow-moving warm front was drawn across north-central FL, extending westward into a weak frontal-wave low over the eastern FL Panhandle/coastal-bend region. The FL surface low initially analyzed near AAF may move only slightly eastward through the day, while the cold front to its south pivots eastward over the northeastern Gulf. The frontal zone to its east should become quasistationary over northernmost portions of FL today, with additional low development possible over Atlantic waters east of JAX. Then from mid/late afternoon onward, the frontal zone should sag southeastward over northern FL, aided by persistent/antecedent precip to its north and isallobaric effects related to the Atlantic cyclogenesis. As these processes occur, near-surface flow should continue to veer gradually with time, slowly reducing both hodograph size, low-level lift, and SRH. However, through the remainder of the morning into early afternoon, this will be concurrent with improved instability south of ongoing clouds/precip. Surface heating of a richly moist airmass south of the warm front, with 70s F surface dewpoints offsetting modest midlevel lapse rates, should yield 2000-3000 J/kg peak MLCAPE. As such, supercell/tornado threat is expected to linger into midday with only a slow decrease in potential as shear diminishes. The damaging-wind threat will last the remainder of the day and into early evening, and perhaps slightly farther south, on at least isolated basis. ....Central Plains... Scattered strong-severe thunderstorms, including supercells, are most likely this afternoon into early evening over central/eastern NE, building southward/eastward with time into parts of northern/ eastern KS, and persisting tonight into western IA and northwestern MO before weakening. Large hail, severe gusts and a few tornadoes will be possible. At 11Z, surface analysis showed a low near MCK, with cold front across western KS to north-central NM, and warm front over southern NE, northern MO and south-central IL. A dryline was drawn over the western TX Panhandle to the Llano Estacado near the TX/NM border, southward into the Big Bend region. This boundary should mix/advect eastward today to western OK, northwestern TX, and the lowest art of the Pecos Valley. Overnight, the cold front will overtake the dryline from north-south. By 00Z, the Plains low should move slowly to central NS and become very nearly stacked with the mid/upper- level vortex center, with which it should maintain vertical continuity through the rest of the period. The 00Z cold front should arc across central KS, northwestern OK, the TX South Plains, and southeastern NM, with warm front across southern IA and central IL. By 12Z, the cold front should extend across eastern KS, south-central OK and southwest TX, with warm front over north-central IL and central IA. A band or arc of thunderstorms, of mixed linear/supercellular character, is expected to develop by midday over NE, near the surface low and adjoining cold-frontal segment, where deep-layer forcing will be maximized. So will assorted measures of vertical shear (deep/effective shear, hodograph size, and vector shear in the boundary layer), especially near the warm front -- but still favorable southward into the warm sector. Forecast soundings suggest 200-400 J/kg effective SRH over much of central/eastern NE and northern KS, locally higher where parcels are still surface- based in the warm-frontal zone, and diminishing southward into southern KS. The eastern rim of the strongest cooling aloft, spreading atop a narrow segment of the warm sector and associated low 60s F surface dewpoints, should combine with limited diurnal heating to support a narrow pre-cold-frontal corridor of 500-1500 J/kg MLCAPE this afternoon. Convective/severe potential southward into OK is more isolated and conditional, given weak to neutral large-scale support, less low- level mass response to the cyclone aloft than farther north, and smaller midlevel lapse rates with southward extent. Still, several models extend enough frontal forcing into north-central/northeastern OK to support at least isolated sustained convection, in an environment that will be at least marginally supercell/severe- favoring. As such, the MRGL area has been extended southward for this cycle. ...Edwards/Broyles.. 10/12/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .