000 ACUS01 KWNS 231258 SWODY1 SPC AC 231256 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0756 AM CDT Sat Jun 23 2018 Valid 231300Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS THROUGH THE SOUTHEAST STATES AND OVER THE MIDDLE ATLANTIC REGION... ...SUMMARY... Scattered severe thunderstorms are expected especially this afternoon and evening from the southern Plains to the lower Mississippi Valley and a portion of the Southeast States. Other severe storms are expected over the Middle Atlantic region. More isolated strong to severe storms might occur over a portion of the central and northern Plains. ...Southern Plains... Persistent regenerative convection and its related cold pool across Oklahoma into far north Texas has continued to reinforce a roughly west/east-oriented frontal zone across the region. This effective front may transition a little northward later today although its latitudinal location later today is a bit uncertain given the persistence of early day convection. Along/south of this boundary, and as far west as a weak surface wave and dryline/surface trough across west-central/western north Texas, the air mass should become moderately unstable by peak heating with 2000-4000 J/kg MLCAPE possible. Owing to hot surface temperatures and modest convergence, isolated to widely scattered thunderstorm development around late afternoon appears most probable across the Low Rolling Plains vicinity of west/north Texas and possibly into southwest Oklahoma, with greater uncertainties for surface-based/diurnally driven development north/northeastward into other parts of Oklahoma given unclear air mass characteristics/recovery. Additional storms may develop farther east-northeast within the frontal zone during the evening as the southerly low-level jet strengthens. A belt of modest winds aloft with 25-30 kt at 500 mb will result in 35-40 kt effective bulk shear near/north of the front where surface winds will remain backed to easterly. Weaker shear will reside in warm sector. Both multicell and some supercell structures will be possible with damaging wind and large hail the main threats from late afternoon into the evening. ...Deep South from the Mississippi River to Georgia/South Carolina... A MCV appears to be aiding the eastward-persistence of an MCS from eastern Arkansas into northern Mississippi/southwest Tennessee early this morning, while MCS-preceding storms have also increased across northeast Mississippi into northern Alabama. For short-term details, see Mesoscale Discussion 835. The MCV and the modest outflow-related cold pool that accompanies it should focus additional development during the day within a destabilizing boundary layer with up to 2500 J/kg MLCAPE possible. A belt of stronger winds aloft accompanying the MCV/shortwave trough will aid storm organization and the environment appears supportive of sub-regional corridors of damaging winds through the afternoon into early/mid evening, perhaps as far east as parts of South Carolina. ...Mid-Atlantic States... A warm front will lift north through Virginia into Pennsylvania during the day ahead of a cold front accompanying a shortwave trough. Diabatic warming of the moist warm sector will result in moderate instability with upwards of 2000-2500 J/kg MLCAPE possible especially from southeast Virginia through the Delmarva into southern New Jersey. A belt of stronger winds aloft will accompany the upper low as it shifts northeast and transitions to an open wave. Storms are expected to develop over the higher terrain with a lee trough across central Virginia also a focus for development. A few splitting supercells will be possible as effective bulk shear increases to 30-40 kt, with storms also organizing into broken bands as they develop east-northeastward. Damaging wind will be the main threat, but some hail will also be possible and a brief tornado cannot be ruled out, particularly with any storms interacting with the warm front where low-level/deep-layer shear will be regionally maximized. ...Wyoming/central High Plains to Middle Missouri River Valley... Ascent accompanying a shortwave trough moving southeast through the northern Rockies and diabatic heating will promote increasing thunderstorm development over the higher terrain of Wyoming into the broader north-central High Plains this afternoon. High based storms capable of downburst winds and severe hail appears to be the main threat. Farther east across South Dakota into eastern Nebraska, a surface trough accompanying a lead shortwave trough will provide a focus for storm development during the afternoon. Modest winds aloft will support multicell storm modes with a few instances of marginally severe hail and gusty winds possible. ..Guyer/Marsh.. 06/23/2018 $$