-- Discussion containing changed information from previous version are highlighted. --
921
FXUS62 KFFC 181742 AAC
AFDFFC

Area Forecast Discussion...UPDATED
National Weather Service Peachtree City GA
142 PM EDT Sat May 18 2024



...New 18Z Aviation Discussion...

.UPDATE...
Issued at 1015 AM EDT Sat May 18 2024

The forecast is on track thus far this morning, so minimal edits
have been made.

Water vapor satellite imagery and radar imagery depict a fetch of
moisture and embedded convection stretching from south-central GA
through the FL Panhandle to the northern Gulf. Strong to severe
storms have generally remained south of the CWA thus far this
morning, where MLCAPE is greatest, although a strong storm cannot
be ruled out across our southern counties. Gusty winds and small
hail would be the primary threats. Otherwise, moderate to heavy
rainfall will persist across our southern counties for the next
several hours as the moisture axis shifts to the south and east.

The shortwave/concentrated area of vorticity currently over the
shared borders of AR/MS/TN will track eastward through the day,
acting as an impetus for scattered to widespread convection across
north GA and portions of central GA. The progression of
scattering/clearing cloud cover will have a major influence on
when/where convection initiates as the day goes on. See the below
short term forecast discussion for information on the anticipated
storm hazards today.

Martin


&&

.SHORT TERM...
(Today through Sunday)
Issued at 411 AM EDT Sat May 18 2024

Much of the Southeast CONUS remains under enhanced southwesterly
upper level flow ahead of a shortwave trough advancing into the
Lower Mississippi River Valley region. Meanwhile, a strong upper
level jet streak is present within the southwesterly flow aloft,
which extends from the central Gulf Coast into the Appalachians.
Showers and thunderstorms have developed across portions of
central and south Alabama and underneath the right-rear quadrant
of this upper jet. These storms will advance eastward, and more
convection will fire near remnant outflow from the MCS that
decayed over south Georgia last night. As such, rain chances will
steadily from southwest to northeast through the early morning
hours, with likely PoPs forecast in portions of west-central
Georgia and chance PoPs elsewhere across the forecast area this
morning and into the early afternoon.

Low cloud ceilings and patchy are in place across much of the
forecast area as the morning begins. Low temperatures and
dewpoints will start the morning primarily in the mid 60s. With
ample moisture the boundary layer, thunderstorms this morning will
have MLCAPE values of as high as 1000-1500 J/kg to work with in
portions of central Georgia. Furthermore, the influence of the jet
streak will contribute to deep layer bulk shear values of 40-60
kts. 0-1 km shear values are also anticipated to range from 20-25
kts. These environmental parameters, along with the orientation of
the aforementioned shear in association with the jet streak, will
allow some thunderstorms to become organized into linear clusters
capable of producing damaging wind gusts. This is anticipated to
become more likely after sunrise, with diurnal heating leading to
increasing surface-based instability.

Speaking of afternoon heating, broken to overcast cloud coverage
is forecast to persist across the majority of the forecast area
today. As such, high temperatures are expected to remain confined
to the mid to upper 70s across the majority of the area. Still,
with dewpoints increasing into the upper 60s by this afternoon,
SBCAPE values are forecast to increase to 1500-2500 J/kg during
the peak heating hours this afternoon. Later this afternoon, the
axis of the shortwave will approach north Georgia, which will
provide forcing for another round of showers and thunderstorms
starting in the far northern tier. With similar shear profiles
from this morning, and also mid-level lapse rates of 6.5-7 C/km, a
few of these storms will also have the potential to become strong
to severe, capable of producing damaging wind gusts and hail.
These storms are forecast to advance southward during the late
afternoon and into the evening, at which point they will begin to
diminish in coverage after sunset with the loss of diurnal
heating.

A caveat to keep in mind is that the behavior and evolutions of
this round of storms will depend on how the airmass recovers after
storms earlier in the day. Furthermore, with precipitable water
values expected to range from 1.5 to 1.8 inches, stronger storms
that occur today are expected to be efficient rainmakers, which
could cause localized flooding concerns where storms train over a
common location. During the overnight hours, the trough axis
itself will move southeastward through Georgia, with the best
forcing and dynamics remaining ahead of the trough. By Sunday
morning, the trough will begin to move offshore of the Georgia
coast and into the Atlantic. The associated vorticity couplet will
still be positioned over eastern Georgia. Combined with a weak
moisture axis, this will result in showers once again on Sunday,
with the highest coverage focused over the eastern portion of the
forecast area. Lift in the vicinity of the trough axis, combined
with diurnal instability, will be sufficient for the development
of scattered thunderstorms among the showers on Sunday. At this
time, severe weather is not expected on Sunday, although an
isolated storm cannot be ruled out.

King


&&

.LONG TERM...
(Sunday night through Friday)
Issued at 411 AM EDT Sat May 18 2024

Sunday evening, we should be seeing the end of our active and wet
weather coming to an end as any remaining showers and
thunderstorms should be tapering off. As the upper level trough
and surface low push off the eastern seaboard, a ridge axis aloft
will begin to orient itself along the spine of the Appalachians
and a surface high will settle in along the lee of the mountains.
As the ridge axis shifts east to become established Monday, a few
terrain induced afternoon showers and thunderstorms may fire
across the northeast Georgia mountains. Otherwise, generally
benign and dry weather conditions are expected outside of these
location`s. There`s still model spread (~5 degrees) in the
guidance over the maximum daytime temperature on Monday,
particularly across eastern Georgia where temperatures will be
moderated depending on how far southwest the extent of the wedge
can become established and whether or not any afternoon storms can
get going in the mountains. Temperatures Monday will be the
coolest of the week with highs in the low to mid 80s for most
locations outside of higher elevations. Temperatures will become
more summer-like by Tuesday with highs in the mid 80s nearly
areawide. A gradual warming trend will continue through the end of
the forecast period into the upper 80s with some locations across
southern central Georgia reaching the 90 degree mark. While the
first half of the long term forecast will be largely dry, a low
amplitude shortwave traversing the Plains will push a weak and
diffuse boundary towards north Georgia, bringing the chance for
rain back into the fold. Chance PoPs are introduced for north
Georgia Wednesday where showers and a few thunderstorms will be
possible. As the weak boundary sags south and becomes quasi-
stationary, showers and thunderstorms will develop along the
boundary across north and much of central Georgia as some weak
disturbances in the quasi- zonal flow pass through. While no
severe weather is expected at this time, instability around
500-1000 J/kg, steep midlevel lapse rates and modest shear could
produce a few strong storms Thursday and Friday.

KAL


&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 122 PM EDT Sat May 18 2024

Expect CIGs to generally improve to low-VFR over the next couple
hours. The main forecast challenge for the afternoon/evening is
timing out convection and thus TEMPOs. Have opted to not do TEMPOs
for MCN and CSG as the atmosphere is quite worked over from SHRA
this morning. For the remaining sites (including ATL), have gone
with TEMPOs for TSRA for either 20z-00z or 21z-01z. Expect
conditions to deteriorate again overnight with widespread IFR and
patchy LIFR expected, as well as fairly widespread MVFR VIS.
Current SW winds will go LGT to calm overnight, then pivot to NE
tomorrow (Sunday) morning.

//ATL Confidence...18Z Update...
Medium confidence on convection timing.
High confidence on all other elements.

Martin
-- End Changed Discussion --


&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Athens          63  78  59  82 /  60  40  10   0
Atlanta         64  79  62  83 /  50  30  10   0
Blairsville     59  75  57  79 /  60  50  10  20
Cartersville    62  80  60  84 /  60  30   0   0
Columbus        65  83  64  84 /  50  20  10   0
Gainesville     63  78  61  81 /  60  50  10  10
Macon           65  80  62  83 /  50  40  10   0
Rome            61  83  61  85 /  60  20   0   0
Peachtree City  64  80  61  83 /  50  30  10   0
Vidalia         68  81  64  81 /  50  60  20  10
-- End Changed Discussion --

&&

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

$$

SHORT TERM...King
LONG TERM....KAL
AVIATION...Martin