Subj : MESO: Mesoscale Discussion 1968 To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 12 2023 19:57:12 ACUS11 KWNS 121957 SWOMCD SPC MCD 121956=20 NEZ000-SDZ000-WYZ000-122200- Mesoscale Discussion 1968 NWS Storm Prediction Center Norman OK 0256 PM CDT Sat Aug 12 2023 Areas affected...west-central SD and the vicinity Concerning...Severe potential...Watch possible=20 Valid 121956Z - 122200Z Probability of Watch Issuance...60 percent SUMMARY...Continued thunderstorm development is expected this afternoon/evening. Severe wind gusts and large hail will be the primary threats. Watch issuance is possible. DISCUSSION...Convective development is underway near the Black Hills northward through northwestern SD. These thunderstorms are located to the northeast of a surface low -- centered over eastern WY -- at the periphery of a low-level warm, moist axis extending northward through western NE and SD. A belt of west-southwesterlies aloft overspreads the northern Plains, with 30-35 kt 500-mb flow currently analyzed over west-central SD. Large-scale ascent in the right-entrance region of this mid-level jet, as well as enhanced surface convergence to the northeast of the surface cyclone, are expected to support continued updraft development and intensification this afternoon in the delineated area. The richest low-level moisture resides to the south, with 60s-F dewpoints reaching to around the SD/NE border. However, temperatures in the lower 80s F and dewpoints generally in the mid-50s F are contributing to MLCAPE around 1000-1500 J/kg in southwest SD. Continued diurnal heating into the mid-80s F should promote sufficiently deep boundary-layer mixing to erode remaining inhibition and support thunderstorm development. Forecast profiles depict rather dry air near the top of the boundary layer and at mid-levels, suggesting realized updraft buoyancy will be tempered somewhat by entrainment. However, straight hodographs with 0-6-km shear around 40 kts should be sufficient to support supercell development with successful initiation attempts. The shear profile will favor updraft splitting early in individual storms' lifecycles, with both flanks offering a threat for severe wind gusts and large hail. Given relatively dry boundary layers and weak low-level shear, individual supercells/clusters should grow upscale by the evening, yielding more of a severe-wind threat thereafter. A Severe Thunderstorm Watch will likely be needed sometime this afternoon to address these threats. ...Flournoy/Smith.. 08/12/2023 ....Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!8IwwZGZ_pfEy1LwgMbBqVCY4iAIwPpS50fAhtoXXPOmT66Kvq9CjOwRgJ8q-WAIKKPzNMDber= pW4cLDIva7CzEIab2Q$ for graphic product... ATTN...WFO...ABR...LBF...UNR...CYS... LAT...LON 43410404 44060433 44640428 44990378 44990227 44650087 43999973 43289960 42700011 42550193 42800335 43410404=20 =3D =3D =3D 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) .