Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Wed Aug 16 2023 07:25:00 ACUS01 KWNS 160558 SWODY1 SPC AC 160556 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1256 AM CDT Wed Aug 16 2023 Valid 161200Z - 171200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE UPPER MISSISSIPPI VALLEY... ....SUMMARY... Strong to severe thunderstorms are expected across parts of the Upper Mississippi Valley during the late afternoon into evening hours. Severe wind and hail are the main threats, though a tornado is also possible. ....Synopsis... A mid-level trough will traverse the Northeast as an upper ridge remains in place across the Interior West today. Across the northern Plains into southern Canada, an upper trough will amplify, prompting rapid deepening of a surface low across Manitoba/Ontario. Strong lee troughing and an associated cold front will trail the surface low and sweep across the Upper MS Valley late this afternoon through the overnight. Ahead of this cold front, adequate boundary-layer destabilization will occur amid strong vertical wind shear, supporting the development of strong to severe thunderstorms, especially by late afternoon onward. ....Upper MS Valley... Though high-level cloud cover may overspread much of the Upper MS Valley during the day, adequate surface heating should still support surface temperatures rising into the 80s F amid low to perhaps mid 60s F dewpoints. 8+ C/km mid-level lapse rates overspreading the warming boundary layer will boost SBCAPE to 2500-4000 J/kg in spots. The cold front will be preceded by a 50+ kt southwesterly 850 mb jet as a 70+ kt west-northwesterly 500 mb speed max approaches the Upper MS Valley, contributing to strongly curved and elongated hodographs and well over 50 kts of deep-layer shear. However, relatively strong capping will also precede the cold front, with strong forcing along the front itself serving as the primary focus for convective initiation. Some brief, transient supercellular development is possible, with large hail and perhaps a tornado possible with any storms that can avoid being undercut by the cold front for any appreciable period of time. However, the strong forcing will likely encourage linear convective development by late afternoon into early evening, with severe wind and occasional bouts of hail being the primary concerns. ....Southeast into the FL Peninsula... Strong heating of a boundary layer, characterized by deep and rich moisture, will encourage the development of pulse-cellular storms and perhaps multicellular clusters (where cold-pool mergers can occur) during the afternoon. Vertical wind shear will be weak, with mid-level lapse rates expected to be mediocre (i.e. at or under 6.5 C/km). Nonetheless, mid to upper 80s/70s F surface temperatures/dewpoints will support SBCAPE over 2000 J/kg. PWATS may exceed 2 inches in locations, and when considering appreciable CAPE density profiles, some of the more intense storms may produce water-loaded downdrafts. A couple of damaging gusts are possible, warranting the introduction of Category 1 (Marginal Risk) probabilities. ....Southwest... Monsoon-driven thunderstorm development is expected by afternoon peak heating across the Lower Colorado River Basin into the Four Corners region. Enough instability may encourage strong storm development, with a severe gust or two possible. At the moment, severe-gust coverage is expected to be too sparse to warrant severe probabilities this outlook. ...Squitieri/Lyons.. 08/16/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .