Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 09 2023 19:40:26 ACUS01 KWNS 091940 SWODY1 SPC AC 091938 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0238 PM CDT Sat Sep 09 2023 Valid 092000Z - 101200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON AND EVENING ACROSS PARTS OF SOUTHWESTERN THROUGH CENTRAL NEBRASKA...PARTS OF EASTERN WYOMING AND ADJACENT PORTIONS OF THE GREAT PLAINS...EASTERN PENNSYLVANIA AND ADJACENT PORTIONS OF THE MID ATLANTIC... ....SUMMARY... Widely scattered strong to severe thunderstorm development remains possible across parts of the northern Mid Atlantic states into southern New England late this afternoon, and across parts of the Great Plains to the east of the Rockies late this afternoon through this evening. ....20Z Update... Categorical and severe probabilistic outlook lines have been adjusted, mostly to account for the continuing gradual progression of synoptic and sub-synoptic scale features and their influence on trends concerning instability. East of the Mississippi Valley, the boundary-layer remains seasonably moist and characterized by moderately large CAPE, along and southeast of a weak surface frontal zone across parts of the Allegheny Plateau into southern Maine. Southwesterly deep-layer mean flow and shear in the vicinity of the front is rather modest (on the order of 20-25 kt or less), but this might still be enough to contribute to some convective organization and marginally higher probabilities for severe wind and hail than areas elsewhere across the east. To the lee of the Rockies, steep lower/mid-tropospheric lapse rates are contributing to moderately large mixed-layer CAPE, but mostly in a rather narrow corridor east of lee surface troughing, from the northwestern Texas Panhandle into the North Platte NE vicinity. For more details on the severe weather potential, please refer to the prior outlook discussion appended below, and the latest SPC mesoscale discussions. ...Kerr.. 09/09/2023 ..PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Sep 09 2023/ ....Nebraska/Kansas and northern High Plains... No changes warranted, with at least widely scattered severe storms including supercells expected across the region later today. Deep-layer wind profiles will be conducive to discrete supercells from late afternoon into this evening, focused along a surface front from central Nebraska to northwest Kansas and within a post-frontal weak low-level upslope regime to the northwest across the northern High Plains. A ribbon of around 1 inch PW values depicted in GOES imagery and sampled by the 12Z LBF sounding should be maintained from western Kansas into central Nebraska. This combined with surface temperatures warming through the 80s along with steep mid-level lapse rates will support a confined corridor of 1000-2000 J/kg MLCAPE. A few to several high-based supercells should develop with large hail as the primary hazard, along with isolated severe wind gusts. This will initially be across central Nebraska and then southwestward into northwest Kansas. A strengthening southerly low-level jet during the evening may support a small cluster evolving south over southwest Nebraska/western Kansas with a continued wind/hail threat. The northern High Plains portion should similarly see a few to several supercells developing off the higher terrain in Wyoming/far southern Montana/southwest South Dakota. While buoyancy will be weaker here and the boundary layer not as deep, 35-45 kt effective shear will be conducive to a few long-track cells capable of producing sporadic hail swaths up to around golf ball size, particularly across east-central/northeast Wyoming. ....Carolinas/Mid-Atlantic/Northeast States.. While overall regional severe coverage will be lesser after a couple of prior active days, along with increasingly meridional and weaker wind profiles, at least isolated damaging winds will again be possible across much of the region. One area of focus for the possibility of a few supercells and slow-moving multicell clustering will be downstream of an MCV over western Pennsylvania. Here, pockets of moderate insolation should support a plume of 1000-2000 J/kg MLCAPE centered on the Delaware Valley. As storms develop and impinge on this buoyancy plume this afternoon, coincident with a mesoscale belt of slightly stronger mid-level flow as sampled by recent KCCX VWP data (30+ kt in lowest 3km AGL), the potential for sporadic damaging winds along with isolated, marginally severe hail should increase. Farther south, a broad plume of weak to moderate buoyancy and steepened low-level lapse rates will support the potential for localized damaging wind gusts. With somewhat weaker mid-level lapse rates and slightly less deep-layer shear relative to farther north, potential for a more organized severe threat appears nebulous at this time. ....South-central/southeast Texas... Hot temperatures in excess of 100 F will again be common to the west of overnight convection outflow (now over the western Gulf of Mexico) and elevated thunderstorms that have redeveloped today across east-central/southeast Texas. While some initial large hail will be possible with storms near the coast, the primary threat should be sporadic severe wind gusts. ....Great Basin... Coincident with a disturbance or two embedded within low-amplitude westerlies, and along the leading periphery of gradually increasing PW values from the southwest, at least isolated high-based thunderstorms are expected to develop later this afternoon. With moderately strong mid-level winds, any of these high-based storms will be capable of producing dry microbursts with severe-caliber wind gusts. $$ = = = 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) .