Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 09 2023 19:54:42 ACUS01 KWNS 091954 SWODY1 SPC AC 091953 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0253 PM CDT Wed Aug 09 2023 Valid 092000Z - 101200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN OKLAHOMA EASTWARD ACROSS THE TENNESSEE VALLEY... ....SUMMARY... Severe thunderstorms capable of producing damaging winds, large hail, and a few tornadoes remain possible from the Ozarks to the Tennessee Valley this afternoon into tonight. ....Discussion... Aside from minor line adjustments -- including a slight southward shift of the risk areas across the Ozarks/Arkansas area and also over northern Lower Michigan -- no appreciable changes appear necessary to the ongoing outlook at this time. ...Goss.. 08/09/2023 ..PREV DISCUSSION... /ISSUED 1141 AM CDT Wed Aug 09 2023/ ....Ozarks/Mid-South/Tennessee Valley... Today's severe-weather scenario remains rather complex, largely owing to persistent regenerative precipitation through midday across the Ozarks southwestward into eastern Oklahoma. Short-term guidance appears to be reflecting typical biases/tendencies regarding later-day destabilization, with the 12z NAM likely too aggressive in destabilization (especially with northward extent), with recent RAP runs much more muted buoyancy-wise and southward focused. Regardless of some uncertainties as far as thermodynamic details and meso-beta spatial preferred severe corridors, rather active severe-weather potential still appears likely across the region later today into tonight, especially in deference to seasonally strong wind fields. Initially, ongoing convection across the Mid-South, in vicinity of far eastern Arkansas and western Tennessee at late morning, may intensify and gradually become surface-based this afternoon as it progresses generally eastward across the Tennessee Valley, especially on the southwest flank of these storms in proximity to the warm front. A favorable wind profile, increasing low-level moisture, and the eastern edge of steeper lapse rates aloft (reference 12z observed soundings from Little Rock and Jackson) will support some supercells capable of large hail, along with some tornado potential. Damaging winds will also be possible as activity congeals into clusters across the Tennessee Valley through the afternoon. For additional short-term details (through early afternoon), see Mesoscale Discussion 1914. After a relatively short convective lull (a few hours at most), a secondary round of severe thunderstorms is expected to initiate near/ahead of the surface cold front/inverted trough across parts of central to southern Missouri into eastern Oklahoma during the late afternoon, with outflow/meso-beta zones of differential heating influential as well. As related to the previously discussed thermodynamic uncertainties, the northward-extent (namely across Missouri) of the more intense/higher-coverage severe storms will be highly dependent upon relatively quick/substantive clearing this afternoon. Deep-layer shear vectors will be at least semi-orthogonal to the initiating front and should support initially discrete supercells amid 45-60 kt effective bulk shear. Strengthening low-level southwesterlies during the evening will further enlarge hodograph curvature across southern Missouri and northern Arkansas. This could foster potential for a couple strong tornadoes, but some of this depends on the evolution of the low-level thermodynamic fields in the wake of early day convection. Where storms intensify/mature, upscale growth is likely this evening as low to mid-level flow fields strengthen ahead of the shortwave trough tracking towards the middle Mississippi Valley. This should result in an MCS tracking southeast along the baroclinic zone trailing northwest in the wake of the early-day storms. The spatial extent and amplitude of severe wind gusts will be modulated by cold pools from prior convection and background nocturnal stabilization to some degree. But given 65-80 kt rear-inflow low-level winds depicted in some guidance, there is conditional potential for a more widespread damaging wind threat with embedded significant severe surface gusts and QLCS tornadoes amid bowing structures/mesovortices. ....Upper Midwest from eastern Dakotas to northern Michigan... Thunderstorms are expected to develop/increase by late afternoon along a southward sagging front across a broad west-to-east expanse, likely in a very isolated manner across the Dakotas with a bit more of a concentration (scattered) across eastern Minnesota into northwest/north-central Wisconsin, and possibly northern Michigan. These storms will mature in an environment with only modest buoyancy (MLCAPE between 500-1000 J/kg), but effective shear values between 30-35 kt. Given storm motions and deep-layer shear vectors largely off the front, discrete to semi-discrete storms are probable. Isolated instances of severe hail and wind are possible, mainly late this afternoon through early evening. $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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