Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Apr 13 2023 12:53:37 ACUS01 KWNS 131253 SWODY1 SPC AC 131252 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Thu Apr 13 2023 Valid 131300Z - 141200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHERN GEORGIA AND EXTREME SOUTHEASTERN ALABAMA... ....SUMMARY... A few tornadoes, along with damaging gusts and isolated large hail, are possible today across parts of the Southeast. Isolated severe gusts also are possible this afternoon over the central High Plains. ....Synopsis... In mid/upper levels, pattern blockiness over the south-central/ southeastern CONUS will erode, as a synoptic-scale trough progresses slowly but steadily across the Intermountain West and Great Basin. Related height falls will spread eastward across the Rockies and adjoining High Plains from MT to west TX. As that occurs, a 500-mb cyclone -- centered initially over southern LA -- will accelerate northeastward, reaching northern AL by the end of the period. At the surface, 11Z analysis showed the low related to the LA cyclone aloft, moving northward near the AL Coast. A warm front was drawn from the low east-southeastward along the FL Panhandle Coast past AAF, then across Apalachee Bay and the north-central FL Peninsula. The surface low should move northwestward across southwestern AL, occlude over southeastern MS, and unite with the mid/upper cyclone center over central MS, around 00Z. By that time, the warm front should reach central AL, south-central GA, and northeastern FL, with a hybrid sea-breeze boundary and broader-scale low-level convergence line southward down Atlantic coastal counties of the peninsula. Overnight, the surface low should fill and take a wobbly path across northern MS. The warm front should moves northward to northern parts of AL/GA and central/southern SC, and weakens somewhat. Meanwhile, under the height falls, a lee trough will become better- defined across the High Plains south of a low analyzed at 11Z near LAR. A wavy front was drawn from the low across western NE, to another weak low between HON-ATY, to southern MN and northern WI. This front should remain quasistationary into this evening. Overnight cyclogenesis over MN will lead to the boundary shifting southeastward as a cold front over northeastern CO, central/ southwestern NE and southeastern SD by 12Z tomorrow. ....Southeast... At least a couple bands of scattered thunderstorms are expected today across the outlook area, with embedded supercells offering the greatest tornado potential, along with sporadic hail. Damaging nontornadic gusts are possible as well. For the near-term threat across the central/eastern FL Panhandle and adjacent parts of southeastern AL and southwestern GA, refer to SPC tornado watch 133 and related mesoscale discussions. The greatest tornado potential will exist locally wherever a sustained, mature supercell can interact with a narrow, northward- shifting corridor in the warm-frontal zone featuring the overlap of: 1. Locally maximized low-level lift, 2. Relatively maximized boundary-layer vorticity, 3. Backed surface flow beneath the southern rim of an easterly to southeasterly LLJ, leading to enlarged hodographs and 150-300 J/kg effective SRH, 4. The northern fringe of a richly moist, surface-based, warm-sector boundary later characterized by upper 60s to low 70s F surface dewpoints, underlying 5. Steep midlevel lapse rates, especially in closer proximity to the cold-core mid/upper low. Diurnal heating, by contrast, may be stronger and longer-lasting with eastward/southeastward extent from the low. The net result should be a northwestward-narrowing corridor of warm-sector MLCAPE extending just into the frontal zone, and ranging from about 1000- 1500 J/kg across most of FL and southern GA, to around 500-1000 J/kg shifting northward over southern/central AL and extreme eastern MS, east of the low. A relative concentration in both convective coverage and CAPE/shear parameter-space overlap has become apparent across parts of southeastern AL and south-central GA, supporting an upgrade in tornado probabilities. Vertical shear farther south down the convergence/sea-breeze zone in eastern FL will lead to messier, more multicellular mode, but with isolated supercells still possible (especially near localized boundary intersections). The overall severe threat should diminish this evening and overnight as the deep-layer cyclone penetrates further inland, the surface low and lift each weaken, and the air mass relative to the warm-front position stabilizes. ....Central High Plains... Isolated to widely scattered thunderstorms are expected to develop this afternoon near the lee trough, in a zone of overlap between favorable diurnal heating (to near convective temperature) and low-level convergence. Activity will form atop a marginally moist, deep boundary layer, with steep low/middle-level lapse rates and generally 40s F surface dewpoints. The main concern will be locally strong-severe downdrafts accelerating through the well-mixed subcloud layer. Diabatic, low-level stabilization should reduce the convective/severe potential with time during early evening. ...Edwards/Smith.. 04/13/2023 $$ = = = 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) .