SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1126 AM CST Fri Dec 18 2020 Valid 191200Z - 201200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MIDDLE/UPPER TEXAS COAST... ...SUMMARY... Isolated strong to severe thunderstorms may occur Saturday across parts of the middle/upper Texas Coast. ...Middle/Upper Texas Coast... A shortwave trough over the southern/central Plains Saturday morning is forecast to move eastward to the lower/mid MS Valley by Saturday evening. At the surface, a cold front will likely extend southwestward across central TX from a weak low near southeastern OK and northeastern TX at the start of the period. Generally elevated thunderstorms may be ongoing Saturday morning across parts of central/east TX in a modest low-level warm/moist advection regime. Weak MUCAPE (less than 500 J/kg) should preclude a severe risk along/north of the cold front through much of the morning. Ahead of the cold front, low to perhaps mid 60s surface dewpoints should advance northward into parts of the middle/upper TX Coast region by midday. Even though diurnal heating will likely be muted by widespread cloud cover and mid-level lapse rates should remain poor, there is some potential for MLCAPE around 250-500 J/kg to develop by early Saturday afternoon ahead of the front along/near the coast. Assuming sufficient boundary-layer destabilization, there will be enough deep-layer shear (40-50 kt) to support updraft organization. Isolated strong/gusty winds should be the main threat with any robust storms that can develop over land, before they move offshore fairly quickly early Saturday afternoon. Even though low-level flow is not forecast to be overly strong, around 100-150 m2/s of 0-1 km SRH may be present very near the coast. Accordingly, a brief tornado cannot be ruled out. Once storms move over the Gulf Saturday afternoon, the marginal severe threat across parts of the middle/upper TX Coast will end. A weak surface low may develop eastward along/near the LA Coast Saturday evening and overnight as the mid-level shortwave trough continues moving eastward. However, the inland advance of substantial low-level moisture appears unlikely, with generally elevated convection expected across LA and the lower MS Valley Saturday night. ..Gleason.. 12/18/2020
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