141
FXUS62 KFFC 241936
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
336 PM EDT Tue Sep 24 2024


...Afternoon Area Forecast Discussion...

.SHORT TERM...
(This evening through Wednesday)
Issued at 334 PM EDT Tue Sep 24 2024

Highlights:

-Increasing rain chances overnight into Wednesday, mainly across
North and north-central GA as far south as metro ATL in response to
an approaching frontal boundary

-Locally heavy rainfall and potential for flooding concerns across
northwest GA on Wednesday

Isolated showers and storms will be possible through the afternoon
today aided by a surface trough in Central GA and southwesterly flow
aloft. Temperatures this afternoon are expected to remain the upper
80s to low 90s. The presence of clouds has tapered temperatures ever
so slightly compared to the previous few days.

Looking ahead to Wednesday -- a 500mb ridge currently of the
northern Gulf will inch eastward as a midlevel trough swings through
the Mid-MS Valley/Mid-South Region. At the sfc, this will bring a
frontal boundary towards the northwestern portions of the forecast
area. As a result, we can expect increasing clouds and increasing
rain chances in our northern zones overnight into early Wednesday
along and ahead of the frontal boundary. Per HREF and hi-res
guidance, rain showers look to begin around sunrise, increasing in
coverage especially through the afternoon. Additionally,
thunderstorm chances increase through the afternoon persisting
through the evening. The biggest thing to note compared to the
previous forecast is increasing confidence on heavy rainfall leading
to flash flooding across much of North GA including the ATL metro
tomorrow (Wednesday) afternoon. Tropical moisture will be on the
increase and will set up ahead of the frontal boundary moving in
from the northwest. Thus, PWs will be upwards of 2+ inches per
latest guidances. An upgrade (from WPC) will be forthcoming for
northeast GA down south including Metro ATL for a Moderate Risk (3
out of 4) of Excessive Rainfall -- i.e. the greatest risk for
rainfall intense enough to cause flash flooding. Latest forecast
totals (for Wednesday only) ranges from 2 to 3 inches with locally
higher amounts. Heavy rainfall and flash flooding potential will be
the main concern for tomorrow (Wednesday) -- note: this is ahead of
anything tropical related. As a result of increasing confidence in
hydro related issues, we have opted to issue a Flood Watch for much
of North and Central GA. This will encompass the threat for
Wednesday and then the evolving threat for the Thursday-Friday
timeframe in association with Tropical Storm Helene. For details
about Tropical Storm Helene please see the long term discussion
below.

Temperatures through the short-term will trend slightly cooler
especially across the north as clouds and rain increase.

07

&&

.LONG TERM...
(Thursday morning through next Monday)
Issued at 334 PM EDT Tue Sep 24 2024

Tropical Storm Helene is forecast to be a major hurricane by the
time it is landfalling along the Big Bend region of Florida late
Thursday. Significant impacts are also expected to be overspreading
the local forecast area by this time as Helene rapidly moves
northward through Thursday night. While model consensus remains
quite good, at this juncture there is still some spread between
ensemble members regarding the exact track of the center of Helene
across our forecast area. A slightly more westerly track would
expose the bulk of the area to more substantial impacts while a
slightly more easterly track would shift the core of the strong wind
and severe threat to eastern zones. Regardless, confidence continues
to increase in substantial impacts for north and central Georgia as
the storm is certain to push into the area in some capacity.

Rainfall: Concern continues to mount for very significant rainfall
totals that would lead to substantial flash flooding and flooding
concerns. Given the expectation that a significant rainfall event is
likely to occur in the short term on Wednesday in advance of the
rainfall associated with Helene, conditions will be well primed for
flooding concerns to become exacerbated on Thursday into Thursday
night. Additional widespread forecast rainfall totals 3.5 to 5" with
locally higher amounts occurring on top of potential 2-3+" rainfall
amounts in some areas on Wednesday. A Moderate Risk for excessive
rainfall is in effect for Thursday across the entire area with some
potential for an upgrade for portions of the area if antecedent
heavy rainfall verifies on Wednesday. A Flood Watch will be in
effect for the entire area.

Winds: The rapid inland progression of Helene will contribute to a
substantial threat for strong winds within the local area. The
strongest winds and gusts will be nearest and just to the east of
the center of circulation, and thus this peak wind area will be
dependent on the eventual track of the center. With that said, gusty
winds will still affect the bulk of the forecast area well away from
the storm`s center as this system will be broad and encompassing.
The time frame within which the strongest winds and gusts are
expected is from late Thursday evening into early Friday morning as
the center of Helene quickly lifts northward. Widespread 35-50 mph
gusts would be increasingly likely for much of the area with higher
gusts anticipated near and east of the center. Higher 50+ mph gusts
will be expected for areas closer to the center.

Tornadoes: A Marginal Risk remains from the Storm Prediction Center
for portions of central GA on Thursday within the eastern quadrant
where tornadoes would be favored. This risk area will likely
fluctuate based on the eventual track of Helene with areas east of
the center favored for short-lived tropical tornadoes.

Thanks to the very quick northward movement, Helene will fortunately
depart the area quickly Friday morning with a drying trend from
south to north. The remnants of Helene will then get absorbed into a
broad closed low over the Mississippi and Ohio Valleys through the
weekend. Isolated to scattered PoPs will hold into early next week.

RW

&&

.AVIATION...
(18Z TAFS)
Issued at 152 PM EDT Tue Sep 24 2024

Latest radar shows widely sct shra this aftn. Iso tsra cannot be
ruled out with marginal instability in place. SCT to BKN cu field
expected through 02z with high clouds increasing. Lower MVFR to
FEw/SCT BKN deck starts to move in ahead of a frontal boundary in
northwest GA after 06z settling in through the metro closer to
12z. Additionally, VCSH starts as early as 14z with onset of -SHRA
between 16-18z. Did introduce a PROB30 for tsra at ATL tomorrow
afternoon. Winds start off from the southwest, become light/vrb
overnight <5kts, and then switch over to the SE side 08z-10z and
stay on this side through 18z.

//ATL Confidence...18Z Update...

Medium confidence on all elements.

07

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          68  83  67  75 /  30  60  70  90
Atlanta         70  81  68  73 /  40  80  80  90
Blairsville     63  73  62  70 /  60  80  80  90
Cartersville    68  79  65  74 /  60  90  80  90
Columbus        72  85  69  75 /  30  80  80  90
Gainesville     68  78  67  72 /  40  80  80  90
Macon           70  87  69  77 /  20  50  70 100
Rome            68  80  66  75 /  70  90  80  90
Peachtree City  68  82  66  73 /  40  80  80  90
Vidalia         70  89  72  80 /  10  20  60  90

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Wednesday afternoon through Friday afternoon
for GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-
078>086-089>098-102>113.

&&

$$

SHORT TERM...07
LONG TERM....RW
AVIATION...07