177
FXUS62 KFFC 231032
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
632 AM EDT Thu May 23 2024



...New 12Z Aviation Discussion...

.SHORT TERM...
(Today through Friday)
Issued at 400 AM EDT Thu May 23 2024

As a strong low pressure system passes over the Great Lakes Region
today, the ridge axis aloft will dampen, giving way to quasi-zonal
flow across the forecast area. As a boundary stalls to our north
across parts of the Ohio River Valley, a disturbance embedded within
the 500mb flow will bring a broader area of convective activity to
our north. The southern extent of this activity is expected to
produce showers and thunderstorms in portions of north Georgia this
afternoon. While it appears that the bulk of the convective activity
is expected this afternoon and evening across north Georgia, how
storms play out remains a bit uncertain at this juncture. Some of
the Hi-Res guidance suggests a range of scenarios including a few
clusters of storms forming into a more organized MCS-like feature
that will ride the northern fringe of the ridge across northeast
Georgia where some models suggest more scattered activity.
Unfortunately, these situations are difficult to forecast and can
often hinge on the evolution of upstream activity. For now, it`s
expected that activity will mostly be confined to locations north of
the metro, but a low end chance for a few showers and an isolated
thunderstorm as far south as the I-20 corridor will be possible
today. Across far north Georgia where most of the activity is
expected to occur, a few storms could become strong to severe. With
surface temperatures in the mid to upper 80s and dewpoints in the
mid to upper 60s, SBCAPE between 1000-1500 J/kg and midlevel bulk
shear between 30-40kt, the environment will be capable of supporting
updrafts with the strongest storms producing damaging wind gusts.
Midlevel lapse rates are marginal, but instances of small hail could
occur in any healthy updrafts that are able to get going today. A
Marginal Risk (Level 1 out of 5) for severe weather is in place
today across portions of north Georgia. For now, QPF is running up
to a quarter inch across north Georgia through the overnight hours,
though with PWATS running between 1.5-2.0", locally higher amounts
may be possible in strong storms and/or if locations are repeatedly
affected.

As convective activity wanes briefly during the overnight hours due
to the loss of diurnal heating, another weak impulse within the flow
could bring another round of showers and thunderstorms to far north
Georgia early Friday morning. Confidence isn`t particularly high at
this point in time, so have relegated PoPs to a high end chance. The
biggest concern Friday will be associated with a stronger shortwave
impulse producing an MCS-type feature during the afternoon hours
that will bring scattered to numerous showers and thunderstorms to
locations primarily along and north of a line from Columbus to Macon
to Wrens. Parameters are looking a little more favorable for
embedded strong to severe storms on Friday with surface temperatures
in the mid 80s to low 90s, dewpoints in the upper 60s, SBCAPE
between 1000-2000 J/kg, steeper midlevel lapse rates of 6.0-6.5+
C/km, and 40-50kt bulk shear. Damaging wind gusts will be the
primary hazard, though hail up to 1 inch may be possible in the
strongest storms. A Marginal Risk (Level 1 out of 5) for severe
weather is currently in place for north Georgia and much of central
Georgia. QPF from Friday morning through Friday evening will be
running between a tenth to three quarters of an inch. Again, locally
higher amounts will be possible in locations that experience
repeated instances of storms and/or strong storms given the
sufficiently moist airmass (signaled by PWATS between 1.25-1.6").

KAL

&&

.LONG TERM...
(Friday night through Wednesday)
Issued at 400 AM EDT Thu May 23 2024

Much of the extended period will be characterized by a progressive
and active upper level flow pattern. Over the weekend, a longwave
trough will advance eastward over the Rockies and dig into the Great
Plains (this system will come into play later in the period).
Meanwhile, the southern tier of the CONUS will remain underneath
quasi-zonal flow aloft, with a parade of shortwave disturbances
quickly traversing the flow. The shortwave serving as the impetus
for shower and thunderstorm activity on Friday will be exiting the
area to the east as the period picks up on Friday night. Any lull in
precipitation will be brief, with another disturbance following
closely behind and moving through the Tennessee Valley region by
Saturday morning. As such, scattered showers and thunderstorms are
expected once again throughout the day in north Georgia and portions
of central Georgia, with the highest chances across the far northern
tier, closest to the shortwave disturbance. The coverage of
thunderstorms will be maximized in the afternoon, when diurnal
instability will be greatest. Speaking of diurnal instability,
high temperatures on Saturday are forecast to range from the upper
80s across much of far north Georgia (with the exception of
cooler temperatures in the northeast mountains) to the mid 90s in
east- central Georgia. These temperatures, combined with dewpoints
in the upper 60s to low 70s, will allow for SBCAPE values between
1500-2500 J/kg each afternoon. Furthermore, with deep-layer bulk
shear values between 30-40 kts, there is the possibility that a
few storms could become strong to severe, capable of producing
damaging winds, hail, and frequent lightning. Because of this, the
SPC has diagnosed a Marginal (level 1 out of 5) Risk for severe
weather across the majority of our area on Saturday.

On Sunday, a more robust shortwave will develop on the southeast
periphery of the aforementioned longwave trough. At this point, a
surface low will quickly develop near the Ozarks region, quickly
deepening over the course of the day as it advances through the
Midwest towards Lake Michigan. Ahead of this system, another hot and
humid day is in store for Sunday, with highs once again ranging from
the upper 80s to mid 90s (5-10 degrees above climatological
normals), and dewpoints in the upper 60s to near 70. As such, there
will be ample instability for the development of scattered
thunderstorms during the daytime on Sunday. The highest coverage is
once again expected to be focused in north Georgia, closest to the
southern extent of the shortwave moving across the midwest. High
SBCAPE values and remaining deep-layer bulk shear values will once
again be favorable for the development of strong to severe
thunderstorms on Sunday afternoon. By Sunday evening, a cold front
extending southward from the surface low will extend into the Deep
South. As it advances southward towards the forecast area, this
front will provide a focus for more organized convective activity on
Sunday evening and into Monday. While some model uncertainty remains
with the progression and timing of the frontal boundary, the
unstable environment combined with increasing 0-1 km shear, 0-1 km
helicity values, and deep layer bulk shear ahead of the front
suggest the potential for severe thunderstorms capable of producing
all threats. Considering precipitable water values increasing to 1.5-
1.8 inches ahead of the front, locally heavy rain will count as one
of these threats with stronger storms that develop. The evolution
of this system will need to be monitored as we get closer to the
weekend.

Slight chance to chance PoPs are forecast to linger on the back side
of the front on Tuesday. However, thunder chances appear that they
will be confined to the far southern portion of the forecast area
where some marginal instability may be present in the afternoon.
Elsewhere across the forecast area, precipitation that occurs is
expected to be light showers. Tuesday into Wednesday, the upper
level flow pattern over the CONUS will become more amplified, with a
broad ridge developing roughly over the Rockies as deep troughing
advances towards the Atlantic Coast. Dry, surface high pressure
associated with the ridge will build into the Southeast CONUS
underneath northwesterly flow at the mid and upper levels. This will
promote benign weather across the forecast area on Wednesday.
Ambient conditions will also be noticeably drier and "cooler," with
dewpoints dropping to the low 50s by Wednesday afternoon and high
temperatures primarily in the low 80s in north Georgia and mid 80s
in central Georgia.

King

&&

.AVIATION...
(12Z TAFS)
Issued at 622 AM EDT Thu May 23 2024

VFR conditions expected throughout the TAF cycle. BKN/SCT cumulus
field expected to develop with cigs at 3kft lifting to 5kft by
the afternoon. Have introduced PROB30 for TSRA at the northern
TAF sites this afternoon and evening. Light SW winds at 5-6KT or
less will become VRB03KT/calm overnight. KAHN will see brief
period of IFR cigs tomorrow morning between 08-09Z. SHRA may be in
the vicinity of KATL during the mid morning hours Friday.

//ATL Confidence...12Z Update...
Low confidence on TSRA. Medium confidence on IFR cigs at KAHN.
High confidence on remaining elements.

KAL

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          67  87  66  91 /  20  30  30  20
Atlanta         69  87  68  89 /  20  40  30  30
Blairsville     62  78  61  84 /  40  60  50  40
Cartersville    66  85  65  89 /  30  50  30  40
Columbus        68  90  70  92 /   0  20  10  20
Gainesville     67  84  67  89 /  20  50  30  30
Macon           68  90  69  92 /   0  10  10  20
Rome            66  84  66  89 /  30  60  40  40
Peachtree City  67  88  67  90 /  10  30  20  30
Vidalia         70  91  71  92 /   0  10  20  20

&&

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

$$

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