Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 211723
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
123 PM EDT Sat Apr 21 2018



.PREV DISCUSSION... /Issued 1033 AM EDT Sat Apr 21 2018/

UPDATE...
High pressure will continue to shift offshore today. Low level
moisture is already on the increase. Latest vis imagery shows
clouds between 5-6kft already pushing northward across central
portions of the state. Have increased the sky cover for the
afternoon. Still think the northern two thirds of the CWFA will
have more sun than clouds, but the southern third of the CWFA may
go bkn by early/mid afternoon.

Otherwise, no major changes needed to the short term portion of
the forecast.

PREV DISCUSSION... /Issued 730 AM EDT Sat Apr 21 2018/

SHORT TERM /Today through Sunday/...

One more dry and mild day is expected as the upper ridge
persists over the southeast. Southerly flow will begin to
increase across the forecast area overnight as a strong
closed upper low starts to move eastward from the Plains.
This low should be in the vicinity of the lower MS Valley
by late Sunday afternoon. Strong southerly flow at 850mb
and increasing PW values will help to produce some moderate
to heavy rainfall rates...but the better chances for heavy
rain look to be just at the end of the short term into the
beginning of the long term. However...pops will be increasing
after 06z Sunday into the daytime Sunday hours. Also...a wedge
will be building over the area tonight into Sunday. This will
keep the air mass mostly stable. Some low CAPE values push into the
far west central area on Sunday afternoon. This could potentially
produce a few thunderstorms around the wedge boundary...but for now
have not included any mention of thunder. No fire weather issued
anticipated for today with RH values remaining above 25 percent.

41

LONG TERM /Sunday Night through Friday/...

Focus continues to be on the heavy rainfall potential from a slow
moving cutoff low interacting with a classical CAD wedge for
enhanced moisture overrunning. Heaviest period looks to be Sunday
night through Monday and updated WPC QPF is still upwards of 4
inches but has shifted the max zone to west central GA and lowered
somewhat in parts of the east. Model solutions are all over the
place as far as where the max zone could be, though at least
consistent on general totals of 3-4 inches (some a bit higher).
Thinking heavier development will be along and near the wedge
front and also enhanced with various upper vort maxes rotating
around the low. Hydrology section included below. Kept thunder
chances in parts of the south for Monday and added a zone farther
northward across eastern portions of the CWA into Monday night
given stronger dynamics with the evolution of the low.

Will also need to watch for some rather strong gradient winds
especially in north GA and higher elevations for Sunday night into
Monday, where models are indicating possible 15-20 kts sustained.
A Wind Advisory may be needed as we get closer.

Aforementioned cutoff low will dampen and lift north into the more
longwave energy by Wednesday, though there remains enough moisture
and shortwave potential to maintain chance pops in the north.
Models continue to have some discrepancies on timing and strength
of two other waves and attendant sfc fronts, though looks to have
the first sometime Thursday and second on Friday. At least the
regime remains mostly stable so not looking at much thunderstorm
potential.

For temps, went decently cooler than guidance for Monday across
the north given strong wedge and the low likely reinforcing. We
should moderate back closer to normals by Wednesday, then more
question late week based on what disturbances may impact the area.

Baker

HYDROLOGY...

Conditions will continued to be monitored for heavy rainfall
potential, most so Sunday night and Monday. The area could receive
amounts of 2 to 4 inches Sunday through Monday night. There is
still some question as to which part of the area is more likely to
see the higher amounts. A flood or flash flood watch could be
needed with future forecasts if confidence increases.

Baker

AVIATION...
12Z Update...
Clear skies will start this TAF set with increasing clouds toward the
late afternoon and into the evening. Clouds already developing in
southeast GA this morning. Think clouds will first start at VFR level
and lower into MVFR this evening. Expect showers to move into the
KATL area after 12z Sunday. Winds will remain on the east side.
Speed should range 10kt to 15kt today and into the evening.


//ATL Confidence...12Z Update...
Confidence high on all elements.

41

&&

.AVIATION...
18Z Update...
Warm front will begin to push northward across the state overnight
and into Sunday. Low level had begun to increase, as noted by the
cu field across south central GA. Do expect MVFR cigs to settle
across the area late tonight/early Sunday as the potential for
shra increases. Think the best thunder chances remain just outside
of the TAF period.

//ATL Confidence...18Z Update...
Med confidence all elements.
NListemaa

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          72  51  66  52 /   0  10  50 100
Atlanta         71  54  64  54 /   0  40  80 100
Blairsville     67  46  60  47 /   0  20  60  90
Cartersville    72  53  64  52 /   0  40  80 100
Columbus        74  58  70  59 /   5  40  90 100
Gainesville     69  51  63  51 /   0  20  60 100
Macon           73  55  70  57 /   5  40  70 100
Rome            73  53  65  52 /   0  40  90 100
Peachtree City  72  53  66  55 /   0  40  80 100
Vidalia         73  57  72  61 /   5  20  50  90

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...NListemaa
LONG TERM....Baker
AVIATION...NListemaa



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