SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1257 AM CDT Mon Oct 25 2021 Valid 251200Z - 261200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE CENTRAL APPALACHIANS INTO VIRGINIA...NORTH CAROLINA...AND SOUTHERN MARYLAND... ...SUMMARY... Thunderstorms associated with mainly isolated wind damage are possible over parts of the southern and central Appalachians into the Carolinas and Middle Atlantic region today. ...Synopsis... A progressive mid-level trough will traverse central Appalachia today, accompanied by a surface low which will impinge on the Mid-Atlantic Seaboard and merge with another surface low traveling up the Atlantic coastline. The initial surface low is expected to weaken with time. However, a 50-70 kt mid-level jet, along with 20+ kts of 850 mb south-southwesterly flow, is expected to overspread a modestly mixed boundary layer across eastern portions of the Ohio Valley towards the Mid Atlantic and Carolinas, supporting scattered strong to severe thunderstorm development. ...Eastern OH Valley into the Mid Atlantic/Carolinas... Severe potential is expected to develop within a broad confluence zone ahead of the cold front across the central Appalachians into Virginia/North Carolina during the afternoon, progressing towards the Mid Atlantic later in the evening. Modest veering of the surface-850 mb winds flow beneath the aforementioned 50-70 kts of mid-level flow will promote 40-50 kts of effective bulk shear. As scattered thunderstorms mature, line segments and transient supercell structures may develop given the presence of 500-1000 J/kg MLCAPE. Damaging gusts are expected to be the main threat, especially across Virginia and northern North Carolina, though a brief tornado could occur with the strongest, longest lasting updrafts. A second area of scattered strong to potentially severe storms may develop across portions of central/eastern OH into WV with a second band of low-topped convection immediately ahead of the surface low/cold front and 500 mb vorticity maxima. These storms will be strongly forced within a region of 30+ kt effective bulk shear, with organization into small line segments/supercells likely despite meager buoyancy (i.e. less than 500 J/kg MLCAPE). Nonetheless, damaging gusts and perhaps a brief tornado or two are possible with the stronger storms in closest proximity to the 500 mb vorticity maxima, and co-located with locally stronger buoyancy. The very modest buoyancy contained within a narrow spatial corridor suggests that the severe threat will be too localized and brief to support an upgrade to Slight Risk this outlook. However, an upgrade may be needed in future outlooks if low-level moisture recovery and boundary-layer destabilization appear more favorable than currently anticipated. ..Squitieri/Mosier.. 10/25/2021 Read more LIVE: spc.noaa.gov
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