SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1128 AM CST Sat Dec 12 2020 Valid 131200Z - 141200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE UPPER TEXAS COAST INTO SOUTHERN/CENTRAL LOUISIANA... ...SUMMARY... Isolated strong to severe thunderstorms may impact parts of the Upper Texas Coast and southern/central Louisiana on Sunday. Damaging wind gusts and perhaps a tornado or two should be the main threats. ...Upper Texas Coast into Southern/Central Louisiana... A southern-stream shortwave trough is forecast to dig across the southern Plains on Sunday, eventually reaching the Southeast late Sunday night. Strong mid-level height falls preceding this shortwave trough will encourage surface cyclogenesis along/near the Upper TX Coast through Sunday afternoon, with this weak low gradually deepening as it moves northeastward across the lower MS Valley and Southeast through the period. A warm front extending to the east/northeast of the surface low should make some northward progress across portions of coastal southeast TX and southern/central LA by Sunday evening. A small warm sector should develop through the day across this area, as modest diurnal heating and surface dewpoints in the low to mid 60s support MLCAPE generally in the 250-500 J/kg range. This weak instability, which will extent through the near-surface layer, will probably be sufficient to support surface-based thunderstorms. A strong wind profile through the troposphere associated with the shortwave trough will likely support 40-50+ kt of effective bulk shear over the warm sector. This will be more than sufficient for supercell structures, although weak mid-level lapse rates may limit more vigorous updrafts to some extent. Isolated to scattered convection should develop by early Sunday afternoon as a low-level jet strengthens, and this activity will move quickly east-northeastward into LA by Sunday evening along/ahead of a cold front. Occasional damaging straight-line winds should be a concern given the strength of the low/mid-level flow, and with the potential for storms to grow upscale into a small bowing line segment. A tornado or two also appears possible, as a veering low-level wind profile and related shear appear sufficient for rotating updrafts. Convection should have a tendency to become elevated into MS/AL as it outpaces the greater low-level moisture in LA, with a lower severe threat Sunday night across the Southeast. Weak forecast instability precludes greater severe wind/tornado probabilities at this time. ...Coastal Alabama into the Western Florida Panhandle... There may be a narrow corridor of surface-based storm potential along the immediate coastal portions of AL and the western FL Panhandle late Sunday night as mid to perhaps upper 60s surface dewpoints return northward. However, the stronger forcing for ascent attendant to the shortwave trough will likely remain to the north of this area. Forecast soundings from various guidance also suggest that a low-level inversion may inhibit robust thunderstorm development with southward extent across the Southeast. ..Gleason.. 12/12/2020
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