163 
FXUS62 KFFC 182025
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
425 PM EDT Fri Jun 18 2021


.SHORT TERM /Tonight through Saturday Night/...

A transition in the pattern is ongoing today as the upper level 
ridge influencing the dry and benign weather conditions moves 
northeastward away from the region and a tropical disturbance 
continues to move northward through the central Gulf of Mexico. High 
temperatures this afternoon will range from mainly 2-6 degrees above 
climatological normals, in the low to mid 90s across the majority of 
north and central Georgia. Southwesterly low level flow has allowed 
for gradual moisture return over Georgia throughout the day today, 
with dewpoints climbing back into the 60s and precipitable water 
values approaching 1". As the short term period begins, isolated 
light showers have begun to develop near the far southern tier of 
the forecast area. Slight chance to low-end chance PoPs are expected 
across south-central Georgia through the remainder of the afternoon 
and into the evening hours today. SBCAPE values of 1000-1500 J/kg in 
that area will be sufficient to support the development of isolated 
thunderstorms. However, severe weather is not anticipated with any 
storms that occur. 

Tonight the focus will shift to the tropical disturbance in the Gulf 
of Mexico. Although uncertainty remains, latest guidance continues 
to trend east with the track of the system. It is forecast to make 
landfall on the eastern Louisiana coastline after midnight Saturday 
morning, then steered northeastward by a weak mid/upper level trough 
it moves inland Saturday morning. Copious moisture will spread over 
Georgia on the east side of this lopsided storm, especially in 
central Georgia, where PWATs will increase to 1.75 to 2+" overnight, 
then areawide during the day Saturday. Cloud cover and rain chances 
will significantly increase over west-central Georgia overnight then 
spread northeastward during the day Saturday and Saturday night. The 
axis of the heaviest precipitation is expected to extend from 
southwest to northeast Georgia during this time period. QPF amounts 
have furthermore trended higher during this forecast cycle and the 
favored time for heavy rain appears to be Saturday night through 
Sunday morning. The Flash Flood Watch has been updated with the 
latest QPF amounts and extended further east. Details on the Flash 
Flood Watch and QPF are included in the Hydrology section below.

SBCAPE values of 1000-1500 J/kg will support the development of 
scattered thunderstorms along with the heavy rain on Saturday and 
Saturday night as the system approaches. Furthermore, 0-1 km shear 
values are anticipated to be between 25-30 kts and 0-1 km storm 
relative helicity values could approach 200 m2/s2. As a result, 
there is a chance for isolated tornadoes on the eastern, "dirty" 
side of the storm Saturday and into Sunday. Heavy rain, 
thunderstorms, and the Flash Flood watch will persist into the 
extended period.

King


.LONG TERM /Sunday through Friday/...

The start of the long-term forecast period bisects the wettest time 
frame as the remnants of the tropical system lift northeastward 
across the area. Sunday morning, the degrading center looks to be 
passing across the CWA, bringing heavy rainfall as it does so. A 
Flash Flood Watch remains in effect for much of the area through 
Sunday given expected widespread QPF in the 2-5" range with locally 
higher totals from Saturday through Monday morning. Flooding 
concerns will thus be at the forefront on Sunday, though a secondary 
threat will be an isolated severe risk given increasing SRH on the 
eastern side of the circulation, particularly across the 
southeastern half of the CWA.

By Sunday evening into Sunday night, the slug of heaviest moisture 
will be exiting eastward with rainfall rates and coverage falling 
off from west to east. With that said, we won't be done with the 
threat for additional heavy rain as the incoming cold front will be 
diving southeastward into the Tennessee Valley on Monday. As we 
remain situated ahead of the front, additional shower and 
thunderstorm development is expected Monday. With a very moist and 
tropical airmass remaining in place, PW values around 2" will 
continue to allow for efficient rainfall rates and at least a 
localized heavy rainfall threat. 

On Tuesday, the front will drop farther southeastward near or into 
the CWA with widespread convection again expected. There remains 
some model discrepancy regarding the extent of the frontal passage 
Tuesday night into Wednesday with the GFS continuing to favor drier 
postfrontal airmass working into north Georgia while the ECMWF hangs 
the front across the center of the area. At this point, continue to 
favor a drier solution across particularly far north Georgia by 
Wednesday into Thursday with PoPs lingering just to the south given 
uncertainty. 

RW

&&

.HYDROLOGY...

The latest WPC forecast continues to favor a widespread 
area of 3 to 5 inches of rainfall over portions of northern and 
central Georgia with localized maxima near 6 inches possible within 
this swath roughly bisecting the County Warning Area near the I-85 
corridor from Saturday through Monday. Much of the forecast area thus 
continues to be included in the Moderate Risk within the WPC's 
Excessive Rainfall Outlook, which does include portions of the 
Atlanta metro area. Given the eastward extension to the heavier 
swath of rainfall, the Flash Flood Watch was extended to include a 
number of counties to the north and east of the earlier extent from 
18Z Saturday to 00z Monday. An additional 1 to 1.5" of rainfall will 
be possible from Monday into Tuesday in association with the 
incoming cold front, with the highest additional amounts more 
probable over northwest Georgia.

&&

AVIATION...
18Z Update...
Primarily VFR conditions are expected through the remainder of the 
day and through the overnight hours. Mid to upper level clouds will 
steadily increase from the south during this time period, lowering 
to SCT-BKN MVFR level clouds by about 12-15Z Saturday morning. 
Some patchy IFR may also be observed where precip occurs. Rain 
chances will also increase from the southwest on Saturday, with a 
PROB30 for SHRA being maintained at ATL from 16-22Z and prevailing
SHRA to begin at 22Z. Winds are expected to be SW through the 
period at mainly 5-10 kts.

//ATL Confidence...18Z Update...
Medium confidence on ceilings during the daytime Saturday.
High confidence on all other elements.

King

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          70  84  68  79 /   0  40  80  80 
Atlanta         71  81  69  77 /   5  60  80  80 
Blairsville     63  81  64  77 /   0  30  70  70 
Cartersville    68  82  68  81 /   5  50  80  80 
Columbus        71  80  70  81 /  30  90  90  80 
Gainesville     70  83  68  77 /   0  40  80  80 
Macon           70  82  69  82 /  10  80  80  80 
Rome            70  83  69  84 /   5  40  70  70 
Peachtree City  69  80  68  78 /  10  70  80  80 
Vidalia         72  84  71  83 /  10  60  70  80 

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from Saturday afternoon through Sunday evening 
for the following zones: Baldwin...Barrow...Bibb...Butts...
Carroll...Chattahoochee...Clarke...Clayton...Cobb...Coweta...
Crawford...DeKalb...Douglas...Fayette...Greene...Gwinnett...
Hancock...Haralson...Harris...Heard...Henry...Jackson...Jasper...
Jones...Lamar...Macon...Madison...Marion...Meriwether...Monroe...
Morgan...Muscogee...Newton...North Fulton...Oconee...
Oglethorpe...Paulding...Peach...Pike...Polk...Putnam...
Rockdale...Schley...South Fulton...Spalding...Stewart...Talbot...
Taliaferro...Taylor...Troup...Upson...Walton...Warren...Webster.

&&

$$

SHORT TERM...King
LONG TERM....RW
AVIATION...King