SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1250 AM CST Sat Nov 28 2020 Valid 291200Z - 301200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY...SOUTHEAST...AND CAROLINAS... ...SUMMARY... Isolated strong to severe thunderstorms may occur Sunday into Sunday night across parts of the lower Mississippi Valley, Southeast, and Carolinas. Damaging winds and perhaps a couple of tornadoes should be the main threats. ...Lower Mississippi Valley into the Southeast and Carolinas... A closed upper low centered over the southern Plains Sunday morning will move eastward through the day. This upper low should begin to merge with a positively tilted, northern-stream upper trough over the eastern states Sunday evening into early Monday morning. A weak surface low initially near the coast of southwestern LA is forecast to develop northeastward across parts of LA/MS/AL through the day while gradually deepening. Additional deepening of this surface low should occur from Sunday night through the end of the period as it continues developing northeastward along/near the spine of the southern/central Appalachians. A warm front attendant to the surface low will lift northward across parts of the Southeast and Carolinas, while a trailing cold front sweeps eastward across these regions through the period. Most guidance indicates that storms will be ongoing Sunday morning over the northern Gulf of Mexico near the LA Coast. Low-level warm advection should be the primary forcing mechanism for this activity, with the low-level jet forecast to shift northward across MS/AL through the day. Some concern remains regarding how much low-level moisture will be able to return inland given the potential for numerous to widespread storms over the northern Gulf of Mexico Sunday morning. If mid to upper 60s surface dewpoints can develop inland across parts of southern LA/MS/AL and the FL Panhandle in tandem with the deepening surface low and northward-advancing warm front, then only modest diurnal heating would be needed to support weak instability and surface-based storms. Strong effective bulk shear of 45-60 kt will easily support organized convection, with supercells possible along/ahead of the cold front. Isolated strong to damaging winds should be a concern given the strength of the low/mid-level flow and potential for storms to grow upscale into a low-topped line along the cold front by Sunday evening. Low-level shear also appears strong enough for updraft rotation, with a couple tornadoes possible across the warm sector with any semi-discrete storms. This isolated severe threat will probably continue across parts of GA into the Carolinas Sunday night and early Monday morning (end of the Day 2 period), as low-level moisture return occurs from the western Atlantic, and as a south-southwesterly jet rapidly strengthens over these areas. However, even though the low-level flow will likely be quite strong, instability is forecast to remain rather weak (generally less than 500 J/kg of MLCAPE). The northern extent of any meaningful damaging wind/tornado threat across the Southeast remains unclear, as there is uncertainty in how far north the mid 60s to upper surface dewpoints will advance. If confidence increases in a narrow corridor of greater instability developing across the warm sector on Sunday, then a Slight Risk for damaging winds and/or tornadoes may be included across some portion of these regions in a later outlook. ..Gleason.. 11/28/2020
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