Special Weather Statement, NWS Atlanta, GA

Area Forecast Discussion
National Weather Service Peachtree City GA
656 AM EST Sat Dec 11 2021

...12Z Aviation Area Forecast Discussion...

.PREV DISCUSSION... /Issued 432 AM EST Sat Dec 11 2021/

SHORT TERM /Today through Sunday/...

Throughout the night, we've watched from afar as a line of tornadic
and damaging storms caused havoc across portions of the mid-
Mississippi River Valley and Midwest, reminding us just how
dangerous and destructive the weather can be. Our thoughts go out to
all those impacted by last night's historic severe weather event.

Closer to home, depending on your location you'd never expect to be
in a pre-storm environment with the CAD wedge just now beginning to
relinquish its hold across the forecast region. A Dense Fog Advisory
has been issued and extended to 15Z across portions of the forecast
area, although visibilities are beginning to improve for Central
Georgia and portions of the far western CWA. Surface southerly flow
will begin intensifying ahead of the incoming frontal system
throughout the morning, forcing the wedge front back to the
northeast as a moist airmass with 60+ degree dewpoints flood into
the area and late morning and afternoon temps climb into the 70s.

This influx of warm, moist air will provide potential for a couple
isolated severe storms this afternoon into the early evening as the
cold front advances into Georgia. A line of storms has already
formed along the frontal system and looks to move into far NW GA
around 18Z this afternoon with a Slight Risk for severe storms for
far NW and west central Georgia. The biggest limiting factor may be
instability, with SBCAPE values progged to max out between 250-750
J/kg in north and western Georgia just ahead of the incoming QLCS,
while SFC-500 mb shear values should be excess of 50 kts. Storms in
this environment should struggle to maintain vertical continuity and
would more likely be sheared off, but momentum transfer and water
loading within downdrafts could pose a threat for some isolated
damaging winds gusts, especially where the QLCS bows toward the
east. Additionally, a couple weak, brief tornadoes cannot be ruled
out either within this environment. 0-1 km shear values are expected
to be around 30-40 kt, with 0-1 km SRH values over 200 m2/s2, should
create a strong zone of shear and vertical vorticity along the QLCS.
However, weaker instability will struggle to take advantage of this
potential, and lack of shear in the 2km-4km range will likely
prevent any long-lived updrafts from sustaining themselves and
instead regular cycling and collapsing of updrafts should be
expected. All in all, the low-level shear is enough by itself for a
couple tornadoes to develop, but any that do form should remain weak
and short-lived. These chances will be mostly likely in far NW and
west central GA, but limited chances are possible throughout the
CWA. As the line of storms move through, looks for kinks within the
line as evidence of enhanced vertical vorticity along the
storm front. Rainfall accumulations on average should be under an
inch.

However, it should be noted that these conditions are dependent on
the wedge retreating from any particular area of interest. The wedge
tends to hang around much longer that expected and has quashed
severe potential in the past. While erosion is forecast, the
location of the wedge front should be monitored as any areas in the
cooler air would have very limited severe potential and areas along
the wedge front could have an increased chance of tornado
development.

Behind the cold front, temperatures should drop quickly with
clearing skies. By Sunday morning most areas north and west of I-85
will see morning temps in the 30s with areas in the higher
elevations likely below freezing for a couple of hours. A sunny and
calm Sunday will follow and highs rebound to very seasonal 50s to
low 60s.

Thiem

LONG TERM /Sunday Night through Friday/...

Looks like a quiet long term period with an upper ridge dominating
the area through the middle of the week. A short wave moves along
the northern Gulf and off the east coast of FL by the start of the
week. However...the effects of this system should remain south of
our area. So we can expect dry weather with a warming trend. The
upper flow becomes more west to southwest Thursday through Friday
as a frontal boundary sinks into the Southern Appalachians. Models
generally agree that the front may reach the TN/GA border by the
end of the period. Have continued with low pops for the far north
late Thursday into Friday.

41

&&

.AVIATION...
12Z Update...
As the CAD wedge continues to erode, LIFR Cigs and VSBYs are
turning to MVFR from the south and west, advancing NEward. ATL
remains the last spot to erode in the metro region with MVFR Cigs,
rising VSBYs and a shift to SWerly winds expected in the next 2-3
hours. CIGs improvement expected to be more gradual between
14-19Z from SW to NW. Line of SHRA and possible TSRA then moving
into are from NW. Potential TSRA timing around ATL b/w 20-23Z,
with lingering -SHRA and MVFR cigs afterward and eventual
improvement to VFR after 00Z.

/ATL Confidence...12Z Update...
Low-Medium on timing of VSBYs and CIGs improvement.
Medium on timing of shift to SSW winds.
High on Precip timing, TSRA potential, and all other elements.

Thiem

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          71  38  56  32 /  90  80   0   0
Atlanta         71  37  55  36 / 100  80   0   0
Blairsville     66  30  54  30 / 100  60   0   0
Cartersville    72  33  55  35 / 100  70   0   0
Columbus        75  42  60  39 /  90  90   0   0
Gainesville     69  37  55  35 /  90  70   0   0
Macon           76  43  62  35 /  70  80   5   0
Rome            72  35  56  33 / 100  60   0   0
Peachtree City  73  35  56  34 / 100  80   0   0
Vidalia         78  52  63  41 /  40  70  20   0

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM EST this morning for the
following zones: Baldwin...Banks...Barrow...Bartow...Butts...
Cherokee...Clarke...Clayton...Cobb...Dawson...DeKalb...Douglas...
Forsyth...Glascock...Greene...Gwinnett...Hall...Hancock...
Henry...Jackson...Jasper...Jefferson...Jones...Lumpkin...
Madison...Morgan...Newton...North Fulton...Oconee...Oglethorpe...
Paulding...Pickens...Putnam...Rockdale...South Fulton...
Taliaferro...Walton...Warren...Washington...White...Wilkes.

&&

SHORT TERM...Thiem
LONG TERM....41
AVIATION...Thiem

Hazardous Weather Outlook
National Weather Service Peachtree City GA
512 AM EST Sat Dec 11 2021

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-121015-
Baldwin-Banks-Barrow-Bartow-Bibb-Bleckley-Butts-Carroll-Catoosa-
Chattahoochee-Chattooga-Cherokee-Clarke-Clayton-Cobb-Coweta-
Crawford-Crisp-Dade-Dawson-DeKalb-Dodge-Dooly-Douglas-Emanuel-
Fannin-Fayette-Floyd-Forsyth-Gilmer-Glascock-Gordon-Greene-
Gwinnett-Hall-Hancock-Haralson-Harris-Heard-Henry-Houston-Jackson-
Jasper-Jefferson-Johnson-Jones-Lamar-Laurens-Lumpkin-Macon-
Madison-Marion-Meriwether-Monroe-Montgomery-Morgan-Murray-
Muscogee-Newton-North Fulton-Oconee-Oglethorpe-Paulding-Peach-
Pickens-Pike-Polk-Pulaski-Putnam-Rockdale-Schley-South Fulton-
Spalding-Stewart-Sumter-Talbot-Taliaferro-Taylor-Telfair-Toombs-
Towns-Treutlen-Troup-Twiggs-Union-Upson-Walker-Walton-Warren-
Washington-Webster-Wheeler-White-Whitfield-Wilcox-Wilkes-
Wilkinson-
512 AM EST Sat Dec 11 2021

This Hazardous Weather Outlook is for portions of North and Central Georgia.

.DAY ONE...Today and Tonight...

A Dense Fog Advisory will remain in effect for portions of north
and central Georgia until 10 AM this morning. Visibilities may
drop to a quarter of a mile or less in areas of dense fog.

Coverage of showers and thunderstorms should become more
widespread today into this evening as a cold front pushes across
the area. At this time...the best chances for thunderstorms should
be by early afternoon for northwest Georgia and late afternoon
into the evening for much of central. Some thunderstorms could be
strong to severe and capable of producing damaging wind gusts.
Severe thunderstorms could also be capable of producing a brief
tornado and locally heavy rain.

.DAYS TWO THROUGH SEVEN...Sunday through Friday...

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not requested but spotters are encouraged
to submit reports of severe weather through the web by going to
weather.gov/atlanta. Please relay any information about observed
severe weather to the NWS while following all local, state, and
CDC guidelines.

Special Weather Statement
National Weather Service Peachtree City GA
919 AM EST Sat Dec 11 2021

GAZ001-002-111445-
Walker GA-Dade GA-
919 AM EST Sat Dec 11 2021

...Strong thunderstorms will impact portions of northwestern Walker
and Dade Counties through 945 AM EST...

At 918 AM EST, a line of strong thunderstorms was along a line
extending from near Cole City to near Fabius, and moving east at 35
mph.

HAZARD...Winds up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Expect minor damage to tree limbs and blowing around of
         light, unsecured objects.

Locations impacted include...
Trenton, Lookout Mountain, Stephensville, Rising Fawn, Chattanooga
Valley, New England, Morganville, Hooker, Cloudland Canyon State
Park, Cole City and Wildwood.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People outdoors should seek shelter immediately.

&&

LAT...LON 3499 8530 3498 8530 3479 8543 3472 8556
      3498 8560
TIME...MOT...LOC 1418Z 281DEG 31KT 3501 8559 3479 8584

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH