SPC Jan 12, 2024 1300 UTC Day 1 Convective Outlook

[NorthGeorgiaWX]

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0650 AM CST Fri Jan 12 2024

Valid 121300Z - 131200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
CENTRAL/NORTHERN MISSISSIPPI AND WESTERN ALABAMA...

...SUMMARY...
Severe thunderstorm winds and a few tornadoes are possible across a
large part of the Southeast through early this evening.  The most
intense gusts (potentially above 70 mph) are possible through midday
over parts of the Mid-South and Tennessee Valley regions.

...Synopsis...
Broadly cyclonic flow in mid/upper levels will cover most of the
CONUS through the period, except for shortwave ridging on either
side of a strong lead trough now over the central/southern Plains. 
That perturbation will be the primary upper-air influence on
convection today.  The southern part -- initially located over
portions of OK and north TX -- should eject northeastward to the
IN/MI border area by 00Z, while the northern part moves more slowly
across IA toward the Quad Cities.  Overnight, these will combine
into a 500-mb cyclone over Lower MI to Lake Huron, increasingly
stacked on the surface cyclone described below. 

The 11Z surface analysis showed an area of low pressure over central
MO, along the northern segment of a cold front extending across
parts of central/western AR to central TX.  A synoptic warm front
was drawn from the low across the lower Ohio Valley.  A prefrontal
trough/wind shift and remnant of a Pacific front was evident over
central LA southwestward to deep south TX.  The surface low should
occlude and move northeastward to near ORD by 00Z, then across Lower
MI overnight.  The main/Arctic cold front is forecast by 00Z to
overtake the Pacific boundary and reach WV, the western Carolinas,
northern/western GA, central/eastern FL Panhandle, and the central
Gulf.  The front should move offshore from the Mid-Atlantic,
Carolinas and GA by 12Z, extending southwestward over central/
southwestern peninsular FL. 

...Southeastern CONUS...
Ongoing lines of strong to severe thunderstorms near the Mississippi
River should consolidate and sweep eastward across parts of the Mid
South toward the Tennessee Valley region through midday -- in and
near the 30% wind/"enhanced" area.  This activity will pose a threat
for severe gusts (some significant/65+ kt), a few embedded
tornadoes, and isolated, marginally severe hail.  See SPC tornado
watch 10 and related mesoscale discussions for near-term coverage of
this convective stage. 

Though peak intensity of the main thunderstorm line is likely to be
in the next several hours, as it encounters the greatest warm-sector
theta-e, some severe-wind and tornado threat may persist eastward
across portions of AL/GA today and into the Carolinas this evening
following very strong low-level warm/theta-e advection.  Additional
strong-severe thunderstorm development is possible over the warm
sector throughout today into this evening, as convergence lines
produce showers that can grow gradually deeper and upscale.  Given
the strength of the wind fields projected to spread over the warm
sector and ahead of the main line, some of this activity may become
supercellular, also with a tornado/damaging-wind/marginal-hail
threat. 

Dewpoints generally reaching the 50s to mid 60s F just prior to cold
frontal passage, and sufficient surface-based instability, should
develop today in the warm sector to offset weak midlevel lapse rates
and support 500-1500 J/kg MLCAPE -- more southward, and mainly south
of I-20 in AL/GA and from the Piedmont eastward in SC/NC.  Forecast
soundings suggest hodographs will be straightening/losing size, but
remaining very long, as the buoyant layer lowers closer to the
surface and the main belt of convection approaches.  Still, that
supports effective SRH locally exceeding 400 J/kg, amidst 60-80-kt
effective-shear magnitudes.  The main limiting factor for areal
severe potential will be lack of greater instability.  Given the
strength of ambient flow, a broad 15% wind area is maintained, with
the understanding that localized pockets of denser wind/tornado
potential may quickly evolve within. 

Farther north across northern TN/KY to southern VA, though MLCAPE
will be weak, intense wind fields and associated convective momentum
transfer still will support some potential for convective gusts to
penetrate near-neutral stability layers and reach the surface.  A
broad area of 60-110-kt winds in the 850-700-mb layer will shift
northeastward across parts of TN/KY and the southern Appalachians
today.  The severe potential in such scenarios is rather spotty and
nebulous, and may extend well northward within cool surface air on
an isolated basis.

..Edwards/Dean.. 01/12/2024

Read more

View the full article