Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Sun Dec 03 2023 09:42:00 ACUS01 KWNS 031243 SWODY1 SPC AC 031241 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0641 AM CST Sun Dec 03 2023 Valid 031300Z - 041200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER WESTERN PENNSYLVANIA AND SMALL PARTS OF ADJOINING STATES... ....SUMMARY... Isolated, marginally severe thunderstorms are possible over western Pennsylvania and small parts of adjoining states this afternoon. ....Synopsis... In mid/upper levels, a series of shortwaves will contribute to eastward movement of a broader-scale trough across the central CONUS and into the Great Lakes/Mississippi Valley region. The two main shortwave troughs involved will be: 1. A leading perturbation -- evident in moisture-channel imagery over parts of IA, eastern MO, and the OK/AR border area. This feature should deamplify somewhat and accelerate east-northeastward away from the mean trough, reaching Lake Erie, western PA and WV by 00Z, then moving offshore from New England around the end of the period. 2. A trailing perturbation -- initially apparent over central/ eastern parts of MT/WY/CO -- and forecast to reach the Mid Mississippi Valley and Mid-South as a strong, compact shortwave trough by 12Z tomorrow. At the surface, 11Z analysis showed a low near PKB, with occluded front southeastward to near LYH, warm front from there across the Hampton Roads area, and cold front over the western Carolinas, western GA, southeastern AL, and western FL Panhandle. That initial low should shift/redevelop poleward over western NY through the afternoon, at the head of the occluded front, while another low forms and shifts along the northeast-moving triple point to near the NJ shore by 18Z, heading seaward thereafter. By 00Z, the cold front should extend from that low across portions of the Carolinas, southern GA, the eastern FL Panhandle, and the northeastern Gulf. ....Western PA and vicinity... A swath of multilayered clouds and precip now over this region is being supported by warm advection and elevated moisture transport. This activity should move east-northeastward into the northern Mid-Atlantic and New England regions through the day. In its wake, a roughly north-south corridor of convection, including a few thunderstorms, should develop this afternoon and move east- northeastward over the region, offering isolated damaging to marginally severe gusts, marginally severe hail, and a conditional/ brief tornado threat. Although the leading mid/upper-level shortwave trough will be weakening as it approaches the area this afternoon, it still should be preceded by a well-developed field of DCVA/ascent aloft. This should combine with low-level warm advection and short window of muted diabatic heating to steepen lapse rates from the surface to midlevels and remove MLCINH, near the occluded front where weak boundary-layer lift will be present as well. This all should support scattered to widely scattered convection with embedded thunderstorms, in an environment characterized by modest buoyancy and intense mid/upper winds. Forecast soundings suggest surface dewpoints generally in the mid-40s to low-50s F supporting MLCAPE in the 200-500 J/kg range. Though flow should be nearly unidirectional through most of the troposphere, 40-50 kt effective-shear magnitudes are possible. Long, nearly straight hodographs may support storm splitting. Activity should weaken as it moves into a more-stable air mass across western/central NY and north-central PA by late afternoon and early evening. ...Edwards/Kerr.. 12/03/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .