SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1225 AM CST Sat Dec 04 2021 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF COASTAL/EAST TEXAS TO THE MID-SOUTH AND LOWER OHIO VALLEY... ...SUMMARY... Isolated strong to severe thunderstorms appear possible mainly Sunday evening and overnight from parts of coastal/east Texas to the Mid-South and lower Ohio River Valley. ...Synopsis... An upper trough initially over the north-central CONUS will likely undergo substantial amplification on Sunday as it digs east-southeastward across much of the Midwest and Great Lakes. A weak upper low over the Baja California vicinity is forecast to move little through the period. Still, low-amplitude perturbations within the southern branch of the mid-level westerlies downstream from the upper low may also aid the amplification of the large-scale upper trough over the lower/mid MS Valley by Sunday night. A surface low initially over the Dakotas Sunday morning will develop eastward towards the Upper Great Lakes by late Sunday night. An attendant cold front is forecast to sweep east-southeastward over much of the Plains, Midwest, and mid MS Valley through the period. ...Coastal/East Texas to the Mid-South and Lower Ohio River Valley... Modest low-level moisture emanating from the western Gulf of Mexico should return northward through the day across much of the southern Plains, lower MS Valley, Mid-South, and perhaps a small part of the lower OH Valley ahead of the advancing cold front. Various model forecast soundings across this region suggest this moisture will likely remain fairly shallow away from the Gulf Coast. Residual low-level capping will probably tend to inhibit robust convective development through much of the day across the warm sector. Still, thunderstorm initiation looks increasingly likely by Sunday evening along or just ahead of the front from parts of eastern OK to the Mid-South vicinity as ascent associated from the amplifying upper trough overspreads these areas. Regardless, MLCAPE should remain fairly weak, generally in the 250-1000 J/kg range, with mid to upper 50s and lower 60s surface dewpoints prevalent. But, both low-level and deep-layer shear are forecast to strengthen quickly Sunday evening and through the overnight hours with the approach of the upper trough. This should foster some convective organization, and isolated strong to damaging winds may occur with thunderstorms that form along the front and quickly become linear while moving east-southeastward. Given the expected strength of the boundary-layer flow and favorable low-level shear as a southwesterly low-level jet strengthens through the evening, a tornado or two also appears possible. The lack of stronger forecast instability currently limits confidence in the potential for a more robust severe threat. There also appears to be some chance for open warm-sector development from parts of east/coastal TX and southeastern OK into AR and western LA Sunday evening/night. Steepened mid-level lapse rates and slightly greater low-level moisture across these areas should support MUCAPE up to 1000-2000 J/kg. Isolated severe hail may occur with any discrete storms that can form given the strong effective bulk shear, in addition to gusty downdraft winds and perhaps a tornado. The convection that develops farther north along the front should outpace the modest low-level moisture return late Sunday night into early Monday morning, especially with eastward extent across the Mid-South into the TN and OH Valleys. Accordingly, these thunderstorms should gradually weaken in this time frame. ..Gleason.. 12/04/2021 Read more LIVE: spc.noaa.gov
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