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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0751 AM CDT Fri Sep 27 2024

Valid 271300Z - 281200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
EASTERNMOST SOUTH CAROLINA OVER PORTIONS OF SOUTHERN/EASTERN NORTH
CAROLINA...

...SUMMARY...
Tornadoes will be most likely through midday and remain possible
into afternoon across parts of the Carolinas and Virginia.

...Synopsis...
In mid/upper levels, a zonal to west-southwesterly belt of flow will
persist from the northwestern CONUS and western Canada into central
Canada, well-removed from a cut-off, cold-core low now evident in
moisture-channel imagery over northern MS.  This low is expected to
pivot slowly northeastward into middle TN by 00Z, then wobble
erratically over that area and/or south-central KY through the night
as it absorbs the remnant vorticity max from what is now Tropical
Storm Helene.

...SC/NC/VA...
The path of center of Tropical Storm Helene finally has turned
northward.  See SPC Tornado watch 688 and associated mesoscale
discussions for near-term coverage of the tornado threat over the
region.  Refer to NHC advisories for the latest track/intensity
guidance on Helene.

The NHC forecast shows that the center should bend northwestward
across southwestern NC, eastern TN and into southern KY through
tonight, weakening greatly and beco*ing more closely conjoined with
the mid/upper cyclone.  For several more hours, into at least
midday, a broad area of strong low-level flow above the surface, and
related large low-level shear/hodographs, should extend well east
and northeast of center across the outlook area, superimposed over:
1.  Relatively maximized low-level convergence, in an arc initially
located over eastern SC into southern NC, preceded by well-backed
surface winds, and forecast to shift northward to northeastward
today;
2.  A richly moist, high-theta-e and weak-MLCINH boundary layer
advecting inland from the Atlantic and characterized by surface
dewpoints co*monly in the 70s F.
These conditions will yield a favorable environment for tornadoes
from any supercells that can cross it, whether within or ahead of
the main spiral/convergence band.  The most probable area for
several supercells to interact with this favorable airmass is over
the 10%/"enhanced" tornado-risk area, with potential decreasing
westward and northward from there due to weaker instability. 

Although the supportive low-level airmass will continue to shift
northeastward over eastern NC and south-central/southeastern VA this
afternoon, tornado potential will diminish with time from
midafternoon into early evening.  This will occur as convection
decreases in coverage and intensity across the area due to a
co*bination of weakening lift and shear, as the remnants of Helene
decay rapidly and back well westward away from the area.  This
process will decouple the remaining stronger low-level flow and
isallobaric forcing away from the most-favorable boundary layer near
the coast, where hodographs should shrink by the hour this afternoon
into evening.

..Edwards/Broyles.. 09/27/2024