-- Discussion containing changed information from previous version are highlighted. --
877
FXUS62 KFFC 181759
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
159 PM EDT Wed Sep 18 2024

...New 18Z Aviation Discussion...

.UPDATE...
Issued at 1148 AM EDT Wed Sep 18 2024

Forecast is generally on track. However, have bumped up cloud
coverage for today starting with satellite derived coverage, then
interpolating through an NBM/NBM 90th percentile blend, then back to
the original forecast by 00Z. /SEC

&&

.SHORT TERM...
(Today through Thursday)
Issued at 443 AM EDT Wed Sep 18 2024

This morning, the post tropical low has drifted over eastern
Tennessee. Calm winds within the relatively moist airmass may produce
areas of patchy dense fog that will last until daybreak. Later
today, a surface low is expected to spin up across central Georgia
along a boundary. Diurnally driven showers and possibly a
thunderstorm are expected this afternoon across far northeastern
Georgia and far central eastern Georgia. The best chance for
precipitation will be in northeast Georgia, while the best
instability, and thus thunderstorm chances, will be focused further
south across eastern central Georgia. However, there remains some
uncertainty over how far west storms could fire this afternoon in
this area. Temperatures will be a bit cooler across north Georgia
where more cloud coverage is expected to linger today. Temperatures
in this area will max out in the low 80s while areas further south
will climb into the upper 80s.

To our west, ridging aloft will begin to build in this evening and
into early Thursday. As the ridge helps usher the low pressure off
the eastern seaboard, skies will begin to clear overnight. Overnight
lows will drop into the 50s in the northeast Georgia mountains with
60s elsewhere. Tomorrow is expected to be dry with a low end chance
of rain in our furthest northeast counties. Under mostly sunny skies,
high temperatures will climb into the upper 80s for most locations
outside of the north Georgia mountains where temperatures will remain
generally in the 70s to low 80s.

KAB

&&

.LONG TERM...
(Thursday night through Tuesday)
Issued at 443 AM EDT Wed Sep 18 2024

Key Messages:

  - Long term remains dry. Very little opportunity for rain until
    the end of the forecast period, and chances still remain low.

  - Increasingly looks like the end of the week into the weekend
    could be quite warm, with temps reaching into the upper 80s
    and even 90s.

Forecast Discussion:

The largest driver of change over the past 24 hours of the long term
seems to be the difficulty the models seem to be having with the low
pressure system over the area. This isn`t surprising - for all
intents and purposes, this is behaving like a cut off low, and models
will always struggle with these features in the absence of strong
upper level flow to push them along. Both the EPS and the GEFS
(alongside their deterministic counterparts) have seen a shift
towards bringing this low and surface low off the coast and then
developing a bit as it pushes towards the northeast. Without anything
to change our airmass, it is allowed to sit for several days and
continue to modify and heat, bringing day time highs into the 80s and
90s by the weekend.

With this low off the coast, a bit more uncertainty has been
introduced over the weekend. The surface high expected to develop to
the north takes a bit more time to push into the area if the surface
low off the northeast is in place, which in turn prevents us from
being "wedged" as fast. The EPS is more in favor of this scenario,
keeping us warmer. The deterministic GFS and some of the GEFS members
also show this, but some of the GEFS hangs on to the idea of the
wedge coming in a bit faster, which would certainly cool us a bit
more than what is in the forecast for Sunday and Monday. This
forecast package will lean towards the wedge being delayed a bit, as
the guidance of late has struggled with the amplitude of these lows
off the coast being a bit underdone, so forecast temps into Sunday
remain in the upper 80s and 90s.

Temps cool down after this as it does still look like a CAD airmass
will move in. Rain chances with this still appear low. After this,
attention may turn to the tropics depending on how development of a
feature there begins in the next few days. Want to note that despite
what one model is showing, there is still considerable spread among
the wider ensemble, showing anything from almost no development to
systems that are just about anywhere in the Gulf. Uncertainty remains
very high overall.

Lusk

&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 150 PM EDT Wed Sep 18 2024

Mostly VFR conditions are expected through the period. However,
thick CU and SC clouds continue across the Atlanta metro area and
AHN. There are some areas of 2500 ft cigs near these terminals, but
cigs should continue to slowly lift through the remainder of the
afternoon. The best chance of MVFR to IFR cigs tonight will be at
AHN, where a tempo 600 ft cig has been included later tonight.
Rain-wise, a few showers are possible later this afternoon around
the Atlanta metro area and AHN. However, models indicate a weak
subsidence inversion at around 750mb, very limited CAPE, and waning
dynamic forcing from the Carolina upper low should keep any activity
to a minimum. Winds will be light, with ATL veering from NW to NE
during the evening hours before possible backing to NNW Thu morning.

//ATL Confidence...18Z Update...
Medium to high for cig heights, high for other elements.

SEC
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          62  85  64  87 /  10  10   0   0
Atlanta         64  87  66  88 /   0   0   0   0
Blairsville     59  80  58  83 /  10  10   0   0
Cartersville    62  87  62  90 /   0   0   0   0
Columbus        66  88  68  90 /   0   0   0   0
Gainesville     63  84  64  86 /  10  10   0   0
Macon           65  87  66  88 /  10   0   0   0
Rome            63  88  62  91 /   0   0   0   0
Peachtree City  62  86  64  88 /   0   0   0   0
Vidalia         67  87  67  86 /  10  10   0   0

&&

.FFC WATCHES/WARNINGS/ADVISORIES...None.

$$

SHORT TERM...SEC
LONG TERM....Lusk
AVIATION...SEC