SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1137 PM CST Wed Dec 23 2020

Valid 241200Z - 251200Z


Severe thunderstorms are expected across the Carolinas and Mid
Atlantic region later this afternoon and evening. A few severe
thunderstorms are also possible across portions of southeast
Alabama, southwest Georgia, and Florida.

...Middle Atlantic/Southeast...

Late-evening water-vapor imagery depicts an expanding/thickening
band of cloudiness across the Arklatex region, indicative of
increasing large-scale ascent ahead of a strong short-wave trough.
Intense mid-level height falls will spread across the Gulf States/TN
Valley region during the day as 130kt 500mb speed max translates
across northern AL into the southern Appalachians by 25/00z. While
the surface reflection in response to this feature will not be
particularly deep, a surface low should track north-northeast from
GA into the eastern WV Panhandle by early evening. As this occurs,
low-level trajectories will become more favorable for Atlantic
moisture to advance inland across Coastal Carolinas as a warm front
lifts to near the VA/NC border at 25/00z, then into the Delmarva
later in the evening. This warm sector advancement will allow for
modest destabilization that will support robust updrafts ahead of
the surging cold front.

Early in the period, a frontal squall line should be ongoing from AL
to extreme southeast LA. This activity may be severe at daybreak,
but higher buoyancy will be noted south of the FL Panhandle which
may ultimately lead to the strongest storms gradually focusing
offshore with time. However, by mid-late afternoon, instability
should improve markedly along the SC/NC Coast as intense southerly
low-level flow strengthens ahead of the short wave. Forecast
soundings depict 1km flow on the order of 60kt with MUCAPE in excess
of 1000 J/kg at ILM by evening. Intense shear and modest
surface-based buoyancy suggest there is a concern for tornadoes with
supercells later this afternoon/evening. Latest high res guidance
support a considerable amount of pre-frontal warm-advection
convection with supercell structures spreading inland by 21z.
Otherwise, some tornado threat will be noted with embedded
circulations along the frontal squall line. Damaging winds are also
expected with the linear MCS as it spreads east.

..Darrow/Gleason.. 12/24/2020

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