SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1255 AM CST Tue Nov 24 2020 Valid 251200Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE LOWER/MID MISSISSIPPI VALLEY INTO THE OHIO/TENNESSEE VALLEYS AND SOUTHEAST... ...SUMMARY... Isolated strong to severe thunderstorms may occur Wednesday across parts of the lower/mid Mississippi Valley into the Ohio/Tennessee Valleys and Southeast. Locally damaging winds should be the main threat, although a tornado or two also appears possible. ...Lower/Mid Mississippi Valley into the Ohio/Tennessee Valleys and Southeast... A closed upper low with associated mid-level southwesterly jet should be centered over the lower/mid MS Valley at the start of the period Wednesday morning. These features are forecast to track eastward across the OH/TN Valleys and Southeast through the day. At the surface, a low initially over northern MO should develop east-northeastward towards the lower Great Lakes by Wednesday evening while gradually weakening. A trailing cold front is expected to move generally eastward across the lower/mid MS Valley, OH/TN Valleys, and parts of the Southeast through the day. A line of showers and thunderstorms should be ongoing along or just ahead of the cold front Wednesday morning across parts of the lower MS Valley into the Mid-South. Only weak destabilization is forecast ahead of this line as low-level moisture gradually increases across these areas. Still, the presence of around 40-50 kt of effective bulk shear and enhanced low-level southwesterly flow suggests a continued threat for isolated damaging winds with the line as it moves eastward through the morning. A tornado or two also cannot be ruled out. The more pronounced large-scale forcing for ascent associated with the upper low is forecast to gradually shift away from the Southeast and TN Valley regions through the day. Additional robust storm development Wednesday afternoon/evening appears uncertain, with low-level convergence along the front providing the main source of lift. If additional storms can form Wednesday afternoon across parts of MS/AL and perhaps middle TN, they could be strong to severe given at least weak instability and sufficient deep-layer shear. Strong/gusty winds would remain the primary threat with this activity through early Wednesday evening. Farther north across parts of the mid MS Valley into the OH Valley, low-level moisture should remain more limited, with mainly mid to upper 50s surface dewpoints possible. These regions will be in close proximity to both the surface and upper low, with somewhat stronger low/mid-level wind fields compared to locations farther south. Cool mid-level temperatures (around -18 to -20 C at 500 mb) associated with the upper low combined with modest diurnal heating ahead of the cold front may support weak surface-based instability by early Wednesday afternoon. A broken, low-topped line of storms may develop across parts of the Midwest into the OH Valley in this high shear/low instability environment. Given the strength of the low-level flow, isolated damaging winds would be the main threat if adequate destabilization occurs. ..Gleason.. 11/24/2020
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