SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0152 PM CST Thu Dec 24 2020

Valid 242000Z - 251200Z


Severe risk -- which includes potential for locally damaging winds
and a few tornadoes -- continues across portions of the Carolinas
and Mid-Atlantic region, and to a lesser degree southward into

Few changes appear necessary to the ongoing outlook at this time, as
convection continues to evolve as expected.  The primary change has
been to remove the SLGT risk area centered over the Florida
Panhandle, as the main convective band has now moved through the
area of relatively greater CAPE.  Though isolated severe risk will
continue across Florida and southeastern Georgia, greater risk
remains farther to the north across the eastern Carolinas and
southeastern Virginia.  Bands of pre-frontal convection will
increase over the next few hours, with an associated uptick in
severe/tornado potential expected.  Later, a frontal band of
convection is forecast to organize and shift eastward across this
region, accompanied by risk for damaging winds and a tornado or two
before moving offshore.

..Goss.. 12/24/2020

.PREV DISCUSSION... /ISSUED 1030 AM CST Thu Dec 24 2020/

...Eastern/central Carolinas and Mid-Atlantic States...
Multi-round severe convection is possible across parts of the region
this afternoon into tonight, particularly for the eastern
Carolinas/southeast Virginia, where semi-discrete warm sector storms
this afternoon/early evening could be followed by a well-organized
convective line late this evening and early in the overnight.

Multi-layer cloud cover remains prevalent at midday across the
region with air mass modification occurring near the coastal
Carolinas where low/middle 60s F surface dewpoints are becoming more
prevalent. North/northeastward-racing bands of convection over the
eastern Carolinas will persist through the afternoon where the
convection should gradually intensify as it becomes rooted within
the increasingly moist/unstable boundary layer, although the
persistent cloud cover and the possibility of a lingering warm layer
aloft leads to some temporal uncertainty. Regardless, extremely
strong low-level/deep-layer shear, accentuated by 55-60 kt in the
lowest 1 km AGL and 300+ 0-1 km SRH, will be supportive of
fast-moving supercells capable of a tornado/damaging wind risk,
particularly late this afternoon through early evening. Given the
magnitude of the vertical shear/SRH, a strong tornado cannot be
ruled out.

Otherwise, as previously mentioned, an additional round of regional
severe risk will likely occur this evening into the overnight as a
strongly forced convective line evolves and spreads
east-northeastward across the Carolinas and coastal
Mid-Atlantic/Delmarva. Damaging winds are the most probable severe
hazard, although a QLCS-related tornado risk may exist as well.

A northeast/southwest-oriented composite convective line across
southern Georgia/Florida Panhandle at late morning immediately
precedes an eastward-moving cold front. Some additional
moistening/diurnal destabilization will occur across the Florida
Peninsula into far southern Georgia ahead of the front/convective
line, with surface-based destabilization otherwise remaining minimal
farther north into central/eastern Georgia. Low-level/deep-layer
winds will further strengthen across the region, although low-level
winds will tend to slowly veer with wind profiles trending more
unidirectional over time. Even with relatively modest buoyancy, this
scenario will support further organization and development of
upscale-growing quasi-linear convective bands this afternoon. An
isolated damaging wind/tornado risk will exist across the region
through the afternoon, with the overall severe risk shifting
eastward/tending to diminish toward and after sunset.

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