SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0158 PM CST Sun Dec 13 2020 Valid 132000Z - 141200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA... ...SUMMARY... A few damaging wind gusts and a couple tornadoes will remain possible across parts of southeast Texas and southwest Louisiana through the early evening. ...20Z Update... No changes have been made to the Slight Risk across parts of coastal southeast TX and southwest LA. A band of pre-frontal showers and thunderstorms should move northeastward across this area through the remainder of the afternoon. Any isolated damaging wind and tornado threat should remain focused along/near the coast, as widespread precipitation aided by low-level warm advection has hampered the northward advance of a warm front inland across southeast TX and southern LA. For more information on the near-term severe threat across this region, see Mesoscale Discussion 1845. It remains unclear whether sufficient destabilization will occur farther north into central LA and southwestern MS to support surface-based storms. Any strong/gusty threat across this area will likely remain marginal and quite isolated. Farther east, mid to upper 60s surface dewpoints should advance northward across southern AL and the western FL Panhandle late tonight into early Monday morning ahead of a surface low and related cold front moving generally eastward across the Southeast. Even though low-level moisture will be increasing across these areas, it appears that instability will be tempered by a low-level inversion and poor low/mid-level lapse rates. With stronger forcing for ascent attendant to a shortwave trough likely remaining to the north of this region, robust convective development late tonight may not occur. Have opted not to include low severe probabilities across southern AL and the FL Panhandle given these potentially limiting factors. ..Gleason.. 12/13/2020 .PREV DISCUSSION... /ISSUED 1023 AM CST Sun Dec 13 2020/ ...Southeast Texas into southwest Louisiana... Late this morning a warm front extends from a weak surface low in southeast TX, eastward to near Palacios TX and into the northwestern Gulf. The front will move north through the day, likely reaching the Houston metro early this afternoon and continuing into the southwest LA coastal area by late afternoon. Rich low-level moisture with upper 60s to 70 F dewpoints reside along and south of the warm front, and will contribute to MLCAPE from 800-1200 J/kg. Numerous showers and scattered thunderstorms are developing across southeast TX within corridor of isentropic ascent north of this boundary. This activity will remain elevated with minimal severe risk. A somewhat greater threat for severe storms should evolve this afternoon. Some CAMs suggest surface-based storms will develop along confluence boundaries just offshore. A couple of these storms might move inland and interact with the warm front where low-level hodographs with 200-400 m2/s2 storm relative helicity and strong effective bulk shear will support potential for supercells capable of producing a tornado or two. Otherwise, additional surface based storms will be possible as the cold front advances southeast and interacts with the moist warm sector. Storms might eventually evolve into linear structures along the cold front this evening as they spread east into LA with a threat for mainly a few strong to damaging wind gusts. The marginal thermodynamic environment with weak lapse rates and widespread low clouds, along with tendency for deeper forcing for ascent to remain north of warm sector, could potentially serve as limiting factors for a more robust severe threat.
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