SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1030 AM CST Wed Dec 30 2020 Valid 301630Z - 311200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS EAST-CENTRAL TO DEEP SOUTH TX... ...SUMMARY... Isolated severe hail and damaging winds, along with a brief tornado will be possible through tonight across parts of east-central to Deep South Texas. ...East-central to Deep South TX... No appreciable change appears needed to the cat 1/MRGL risk area, although an adjustment has been made to expand the underlying wind/tornado probabilities for this afternoon's convective threat in east-central/southeast TX. A shortwave trough over western Chihuahua will gradually progress east-southeast towards the Coahuila/Durango border area through 12Z tomorrow. In the wake of a northern stream shortwave trough, a surface cold front will move southeast across eastern to south TX through the period. The movement of the front will slow later tonight in response to weak cyclogenesis near the lower TX, in the zone of ascent downstream from the northern Mexico trough. This pattern will also maintain a broad southerly low-level jet across the TX coast that should diurnally weaken through sunset before strengthening again late tonight, with a continued inland transport of mid to upper 60s boundary-layer dewpoints. The severe threat will probably occur within two phases, one this afternoon across a portion of east-central/southeast TX and the other overnight towards the middle TX coast. A pre-frontal confluence arc of convection is ongoing just ahead of the impinging cold front across central TX. A few cloud breaks ahead of this arc should yield thin MLCAPE increasing to between 500-1000 J/kg. While guidance generally suggests low-level flow will subside somewhat this afternoon (with the RAP appearing more aggressive than the NAM/ECMWF), modest hodograph curvature might prove sufficient for a lower-end supercell or two capable of producing all hazards. The undercutting nature of the front will further limit longevity of any surface-based supercell. After a potential lull in the severe threat this evening, the risk for a severe storm or two should slowly increase after 06Z tonight as deep-layer and low-level shear gradually strengthen in the confined warm sector near the lower to middle TX coast. The bulk of a greater tornado threat should still await until after 12Z in the D2 period. ..Grams/Dean.. 12/30/2020
There’s more click here.