Subj : DAY2SVR: Nws Storm Predic To : All From : Mike Powell Date : Mon Jul 17 2023 15:41:00 ACUS02 KWNS 171731 SWODY2 SPC AC 171729 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1229 PM CDT Mon Jul 17 2023 Valid 181200Z - 191200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF THE LOWER-MISSOURI/MID-MISSISSIPPI VALLEY... ....SUMMARY... Thunderstorms associated with large hail and damaging wind gusts will be possible Tuesday evening into the overnight across parts of the mid Mississippi/Lower-Missouri Valley. Other strong to severe storms will also be possible in various parts of the CONUS from the Great Basin and the Plains to the Midwest and East Coast. ....Synopsis... The upper level pattern on Tuesday will feature a flat ridge across the western CONUS with a mid-level shortwave trough crossing Montana, another mid-level shortwave trough across the Corn Belt and a broader trough across the Great Lakes into the Northeast. The surface pattern will more nebulous with a diffuse surface front extending from the Northeast across the southern Great Lakes and into the Plains. Across the Plains, it will be a more defined warm front with a surface low across Kansas. This front will extend north from that surface low into the northern Plains. ....Lower Missouri Valley/Mid-Mississippi Valley/Lower Ohio Valley and Vicinity... Thunderstorms will likely be ongoing at the beginning of the period in one or more locations along a zone of mid-level frontogenesis extending from southeast South Dakota to northern Arkansas. Mid level height falls and the associated low-level jet response are expected to overspread the frontal zone between 06 and 12Z, but forecast soundings along this zone show varying low-level moisture which likely explains the variance in convective coverage along this zone from 12Z CAM guidance. This morning convection will have a significant impact on the forecast in the region. More widespread morning convection and development of a cold pool could support a severe weather threat tomorrow morning and continuing through the afternoon. However, if this does not occur, the warm sector would likely remain mostly capped during the day. Regardless of the evolution of morning convection, the signal remains strong for elevated convection along the Mississippi River near St. Louis during the overnight period as a 40-50 knot low-level jet develops across eastern Missouri amid 2000+ J/kg MUCAPE and 45-50 knots of mid-level flow. This will support the potential for elevated supercells along this zone starting between 04Z and 07Z late Tuesday night. Eventually these storms may grow into a forward propagating MCS with a severe wind threat into portions of western Kentucky/northern Tennessee early Wednesday morning. ....Northern Plains... Thunderstorms are expected across the northern Plains on Tuesday afternoon as cyclonic vorticity advection overspreads the region near peak heating. MLCAPE around 2000 to 2500 J/kg amid 35 to 40 knots of effective shear should support supercells developing along the frontal zone. Boundary normal flow should keep convection discrete and perhaps somewhat isolated. If more widespread storm coverage is anticipated, a slight risk may be needed for this region in later outlooks. ....Central High Plains... A few thunderstorms are possible late Tuesday afternoon as low-level flow veers from northeasterly to easterly and becomes more upslope with low-level moisture advection on the northern periphery of the surface cyclone. The favorable period may be relatively short lived since moisture arrives late, but a favorable environment may develop with 2000+ J/kg MLCAPE and a supercell wind profile. ....Eastern Carolinas to the Northeast... A broad region of weak ascent is expected from the Appalachians eastward as a mid-level trough translates eastward. Ahead of this trough, pockets of strong instability are expected to develop with the greatest instability across the eastern Carolinas. The most favorable shear is expected across portions of the Northeast where long, straight hodographs could support some supercells capable of large hail and damaging wind gusts. ....Great Basin... A deeply mixed airmass is expected Tuesday across the Great Basin with ample instability for scattered thunderstorms across much of the region. A belt of stronger mid-level flow around 30 knots will exist from east-central Nevada and across north-central Utah. This may support some storm organization with the potential for isolated severe wind gusts given the deeply mixed sub-cloud layer. ...Bentley.. 07/17/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .