Subj : DAY1SVR: Marginal Risk To : All From : Mike Powell Date : Sat Oct 28 2023 09:37:00 ACUS01 KWNS 281247 SWODY1 SPC AC 281246 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 AM CDT Sat Oct 28 2023 Valid 281300Z - 291200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF WEST TEXAS AND EXTREME SOUTHEASTERN NEW MEXICO... ....SUMMARY... Isolated severe thunderstorms may develop late this afternoon into the evening over parts of west Texas and extreme southeastern New Mexico. ....Synopsis... In mid/upper levels, a positively tilted longwave trough will persist from Baffin Island in Arctic Canada, southwestward across south-central Canada to the Great Basin and central/southern CA. This feature will be sharpened somewhat in definition, as several shortwave troughs traverse the associated cyclonic flow near the mean trough. Though all of the shortwaves will remain well north and northwest of the outlook area discussed below, broad, low-end height falls are expected to occur ahead of the longwave trough, from northern MX, west TX and the southern Rockies across the central/northern Plains to the Great Lakes. At the surface, a cold front was analyzed at 11Z from Lake Ontario across the lower Ohio Valley to central/southwestern AR, with a weak low in the DEQ area, and the front becoming quasistationary southwestward over central TX to the Permian Basin and southeastern NM. A dryline was drawn from a frontal intersection just east of GDP southward near PRS, and should move only slightly eastward today. The cold front should proceed eastward/southeastward across the northeastern CONUS and Ohio Valley today, moving to near the southern New England Coast, northern VA, eastern KY, western TN, and central AR by 00Z. The low should ripple north-northeastward along the boundary and over western AR today, while the front to its southwest remains quasistationary. By 12Z tomorrow, the front should extend from the southern Delmarva/Chesapeake Bay area across southern WV to a relocated/redeveloped frontal-wave low over northern KY, then southwestward across the Arklatex and central/west TX. ....Portions of west TX and southeastern NM... Isolated to widely scattered thunderstorms are possible this afternoon, developing initially over higher terrain or the dryline, in the Guadalupe/Davis Mountains vicinity and moving northeastward to eastward across the outlook area. Large hail will be the main concern. Although large-scale support will be weak at best, the combination of modest MLCINH (due to lack of more-substantial EML), lift from diurnal heating, a weak upslope-flow component, and vertical circulation of the dryline all will foster potential for development and maintenance of convection by mid/late afternoon. A narrow warm sector, with surface dewpoints commonly in the 60s F, should support MLCAPE in the 1000-1500 J/kg range, amidst weak near-surface shear but favorable boundary-layer and effective shear (35-50-kt values by both measures). Despite small hodographs below about 1 km, their size above that yields effective SRH of 150-300 J/kg, with highest values along the front. Given a sharp transition to cold air northeast of the front, cells moving over the boundary should become elevated quickly and likely weaken substantially. 30-40-kt nocturnal LLJ development is progged over the lower Pecos Valley region, which may support additional strong thunderstorms this evening and tonight over the cold side of the front. However, hail potential with that episode looks very conditional and marginal at this time, given weaker buoyancy aloft and potentially quick transition to messy storm mode. ...Edwards/Goss.. 10/28/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .