SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1148 PM CST Sat Dec 12 2020 Valid 131200Z - 141200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MIDDLE/UPPER TX COAST INTO SOUTHEAST TX AND CENTRAL/SOUTHERN LA... ...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 are the main threats. ...Middle/Upper Texas Coast into Southern/Central Louisiana... Shortwave trough currently moving through the Four Corners region is forecast to continue quickly southeastward, reaching the southern High Plains by later this morning. This shortwave is then expected to pivot more eastward across the southern Plains and Lower MS Valley, while also obtaining a more neutral tilt. This transition to a more neutral tilt will also be accompanied by strengthening mid-level flow as well as increasing low-level flow throughout the warm sector and surface cyclogenesis. Surface low resulting from this cyclogenesis will likely develop along the middle TX Coast before moving northeastward across central LA and into central MS. This path will limit the inland penetration of the warm sector, with low 60s dewpoints likely remaining confined from the middle TX coast in southeast TX during the day. Later this evening and overnight, low 60s dewpoints will likely reach central portions of the Lower MS Valley and Southeast states. Primary forecast concern is whether or not surface-based storms will be able to establish within the warm sector over southeast TX/Upper TX Coast. Based on forecast soundings, surface temperatures likely need to reach the low/mid 70s for surface-based storms, which appears most probable from the middle TX Coast into southwest LA in the 18 to 21Z time frame. Given the impressive kinematic profiles, the expectation is that any warm-sector storms that are able to persist and maintain updraft continuity should be able to organize into supercells. Primary threat would be damaging wind gusts, but a tornado or two is also possible. One additional factor working against tornadogenesis (in addition to limited instability and a potentially elevated storm structure) is the anticipated veering of the low-level winds during the afternoon ahead of the cold front. A strongly forced, but narrow line of storms is anticipated along the front in the wake of the earlier warm-sector activity. A few stronger gusts are possible from the middle TX coast into southern LA as this line moves through. Low-level stability will likely limit strong gusts at the surface across much of east TX and northern/central LA, but potential exists for a few gusts to be strong enough to penetrate the stable layer. Overnight, storms should have a tendency to become more elevated with eastern extent into the Southeast as the system outpaces the low-level moisture along the coast. ..Mosier.. 12/13/2020
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