SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1255 AM CST Tue Dec 22 2020 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MIDDLE TX COAST EASTWARD ACROSS MUCH OF LA...MS...AL AND FL PANHANDLE... ...SUMMARY... Isolated severe thunderstorms are possible from the middle Texas Coast across much of Louisiana, Mississippi, Alabama, and the Florida Panhandle. ...Synopsis... A deep upper trough is expected to extend from the Canadian Prairie Provinces southwestward into the Four Corners early Wednesday morning. Several shortwave troughs will rotate through this parent upper trough, contributing to both eastward progression and continued deepening. Upper flow around the trough will also strengthen significantly throughout the period, with a corridor of 100+ kt 500-mb winds expected from the Lower MS Valley into southern Ontario by early Thursday morning. At the surface, low associated with the lead shortwave embedded within the larger upper trough will begin the period centered over east-central MN/northwest WI. A strong cold front will extend from this low southwestward through the Mid MO Valley and OK into southwest TX. Fast eastward/southeastward progression of this front is expected throughout the day, and the front will likely extend from eastern Lower MI south-southwestward into the western FL Panhandle by 12Z Thursday. Moisture return is anticipated ahead of this front, with low 60s dewpoints likely in place before frontal passage from the middle TX Coast eastward along the central Gulf Coast and into the FL Peninsula. Abundant cloud cover ahead of the front will limit heating and lapse rates will remain poor, resulting in only modest buoyancy. In addition, much of the pre-frontal activity will be induced by warm-air advection and elevated above a shallow stable layer. That be said, surface-based storms do appear possible along the coastal areas of the middle and upper TX coast eastward along the central Gulf Coast and into the FL Peninsula where dewpoints may reach the mid 60s. Low to mid-level wind fields will be strong, supporting stronger storms with any more persistent and deep updrafts. Any tornado threat will be confined to areas mentioned above where surface-based storms are most likely. Uncertainty is too high to introduce 5% tornado probabilities with this outlook, but two areas may merit an upgrade in later outlooks. One is along the middle/upper TX coast where mid 60s dewpoints and modest heating may result in greater instability. The other is over the FL Panhandle and adjacent southern AL where strong low-level flow is anticipated early Thursday morning. Additionally, damaging wind gusts are possible along and just ahead of the front as it moves across the Southeast. Much of this threat will be north of the warm front, but occasional gusts should be able to penetrate the shallow stable layer and manifest at the surface. ..Mosier.. 12/22/2020
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