SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1238 AM CST Wed Dec 30 2020 Valid 311200Z - 011200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF FAR SOUTHEAST TEXAS...THE LOWER MISSISSIPPI VALLEY AND CENTRAL GULF COAST STATES... ...SUMMARY... Severe thunderstorms associated with a tornado threat and wind damage will be possible Thursday into Thursday night from far southeast Texas into the lower Mississippi Valley and across the central Gulf Coast States. ...Far Southeast Texas/Lower Mississippi Valley/Central Gulf Coast States... An upper-level low will move from northern Mexico into central Texas on Thursday. The associated upper-level trough will become negatively-tilted as a 70 to 90 kt mid-level jet rounds the base of the system. During the day, the moist sector will extend from the far southeast Texas eastward across Louisiana, southern Mississippi and southern Alabama. A surface low will move north-northeastward across the far western edge of the moist sector. Near the surface low, a large cluster of thunderstorms will be ongoing in the Texas Coastal Plain at the start of the period. This convection will be supported by large-scale ascent associated with the nose of the mid-level jet. The cluster of storms will move east-northeastward to the upper Texas Coast by afternoon and into the lower Mississippi Valley by early evening. Ahead of the cluster of storms, model forecasts increase MLCAPE into the 500 to 1000 J/kg range over much of the moist sector. In spite of the weak instability, the mid-level jet will create strong deep-layer shear profiles, which will be favorable for severe storms. A severe threat is forecast to first develop in far southeast Texas early Thursday afternoon as a 50 to 60 kt low-level jet moves inland across southwestern Louisiana. The severe threat should be the greatest along and ahead of a pre-frontal trough, which will progress eastward across southern Louisiana during the late afternoon and early evening. At that time, low-level shear is forecast to become maximized due to the presence of the 850 mb jet. The jet will create 0-3 km storm relative helicities of 300 to 400 m2/s2, which will support a tornado threat with the more dominant rotating storms. The tornado threat may become maximized in southeastern Louisiana during the late afternoon and early evening, near a pocket of moderate instability. Wind damage will also be possible with the stronger thunderstorms embedded in the cluster. The severe threat is expected to continue across southern Mississippi and southern Alabama during the mid to late evening. The threat may persist into the early overnight period, especially if a line of strong thunderstorms can persist. ..Broyles.. 12/30/2020
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