SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0228 AM CDT Thu Apr 22 2021 Valid 241200Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHEAST... ...SUMMARY... Isolated to scattered severe thunderstorms may occur Saturday across parts of the Southeast. All severe hazards appear possible, including large hail, damaging winds, and a few tornadoes. ...Southeast... An upper trough should continue moving eastward from the lower/mid MS Valley across the Southeast and Mid-Atlantic on Saturday. A strong south-southwesterly low-level jet is forecast to advance quickly eastward from AL Saturday morning across GA and into SC by the afternoon. At the surface, a weak low over the lower MS Valley and Mid-South should develop northeastward towards the central Appalachians during the day, with some uncertainty whether it deepens substantially or not. Regardless, rich low-level moisture should move northward across AL/GA/SC, supporting a threat for surface-based thunderstorms. Strong to severe convection may be ongoing Saturday morning from portions of southern LA into MS and AL in association with the low-level jet. As this activity spreads eastward through Saturday afternoon, it may continue to pose at least an isolated severe threat so long as it does not outpace the low-level moisture return. A rather strong mid-level jet attendant to the upper trough will support similarly strong deep-layer shear. Forecast soundings across the warm sector in GA/SC from both the 00Z NAM and ECMWF show a veering/strengthening wind profile with height through mid levels, potentially supporting supercells. Some eastward advection of an EML from the Plains also appears possible across the warm sector, which combined with the increasing low-level moisture and diurnal heating should foster moderate to locally strong instability along/south of the warm front. All severe hazards, including the potential for a few tornadoes, appear possible given the favorable thermodynamic and kinematic environment forecast as thunderstorms move eastward across the Southeast through the afternoon and early evening. The main uncertainties are the possible limiting effect of morning convection on the development of instability, and predominant storm mode. Finally, there also appears to be a conditional threat for severe thunderstorms behind the initial morning activity across southern LA into MS/AL, as strong instability should develop ahead of an eastward-moving cold front. However, low-level flow is forecast to quickly veer to westerly behind the passage of the previously mentioned low-level jet. This should limit convergence along the front, and the most pronounced large-scale ascent associated with the upper trough should be mostly east of this region by Saturday afternoon. Even so, if convection can develop in this regime, then both isolated large hail and damaging winds would be possible. ..Gleason.. 04/22/2021
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