Subj : DAY1SVR: Enhanced Risk To : All From : Mike Powell Date : Wed Aug 09 2023 08:22:00 ACUS01 KWNS 091251 SWODY1 SPC AC 091249 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0749 AM CDT Wed Aug 09 2023 Valid 091300Z - 101200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OZARKS TO THE TN VALLEY... ....SUMMARY... Multiple rounds of significant severe thunderstorms with tornadoes, and damaging winds/hail are possible from the Ozarks to the Tennessee Valley this afternoon into tonight. ....Ozarks to the TN Valley... A complex severe weather scenario is anticipated through tonight with multiple rounds of intense severe thunderstorms possible. Within a high ceiling but low floor setup, the middle risk level (3 of 5) remains appropriate given the degree of uncertainty/failure modes at this outlook cycle. Primary adjustments are to add significant severe areas across the hazards to indicate the potential of a higher-end outcome. Extensive elevated convection is ongoing across parts of the Ozarks to an MCV evident in east KS. This activity may decay somewhat but will likely persist through midday amid a robust low-level warm theta-e advection regime downstream of the primary shortwave trough over the central High Plains. Along the southern extent of this regime, convection may transition to becoming surface-based over parts of the Mid-South towards midday as the leading edge of mid 70s surface dew points advects northeast from the Ark-La-Miss. CAM guidance consensus suggests potential for relatively pronounced 2-5 km UH within a favorable wind profile for mid-level updraft rotation. Significant severe hail should be the primary initial threat with discrete supercells along the leading edge of steep mid-level lapse rates. Damaging winds and a couple tornadoes will also be possible as activity congeals into clusters across the TN Valley through the afternoon. A second round of severe thunderstorms should develop near/ahead of the surface cold front/inverted trough across parts of central to southern MO into eastern OK during the late afternoon. Guidance depicts wide variation in the northern extent of air mass recovery today along the trailing outflow/differential heating corridor. The gradient across the baroclinic zone will be quite pronounced owing to hot temperatures across TX into southern OK exceeding 100 F versus low 70s holding in parts of MO. 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 MO and northern AR. This could foster potential for a couple strong tornadoes, but will likely be highly dependent on the evolution of the low-level thermodynamic fields in the wake of earlier convection. ARW-based CAMs and the 06Z RRFS are insistent on prominent upscale growth occurring tonight as low to mid-level flow fields strengthen ahead of the aforementioned shortwave trough tracking towards the Mid-MS 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 forecast soundings, there is conditional potential for a more widespread damaging wind threat with embedded significant severe surface gusts and QLCS tornadoes amid bowing structures/mesovortices. ....U.P. of MI to the eastern Dakotas... Isolated thunderstorms developing along a diffuse cold front will mature in an environment with only modest buoyancy (MLCAPE between 500-1000 J/kg), but effective shear values between 30-35 knots. Given storm motions and deep-layer shear vectors largely off the front, discrete to semi-discrete storms appear probable. A similar environment yesterday supported isolated severe storms, and this should be the case again today farther south and in a bit wider corridor over the Upper Midwest. ...Grams/Dean.. 08/09/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .