Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 212331
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
631 PM EST Tue Nov 21 2017



.UPDATE...
Updated for the 00Z Aviation Discussion.

&&

.PREV DISCUSSION... /Issued 252 PM EST Tue Nov 21 2017/

SHORT TERM /Tonight through Wednesday Night/...

Weak high pressure off the southeast coast will continue to build
away from the forecast area, and surface winds will shift to the
north and northwest overnight.  The tail end of a longwave trough
will shift across north Georgia through tomorrow afternoon.  The
trough will help pull an inverted surface wave just south of the
forecast area through early tomorrow evening.  These features will
bring a quick shot of increased moisture across the area tonight,
with some clearing beginning in the northwest by mid morning
tomorrow as cool high pressure builds into north Georgia.  Only
limited rain chances through the period, slight chance tonight with
isolated pockets of light rain showers.  Best chances, albeit low
chance, will be across central Georgia tomorrow night as surface
wave moves across south Georgia.  With good moisture tonight, and
winds diminishing to near calm before increasing out of the
southwest tomorrow morning, we could see patchy fog develop by
midnight or shortly after.  We should see fog burn off quickly
tomorrow as drier air filters into the forecast area.  Short term
models are in good agreement with the overall pattern and guidance
temperatures are also close through the period.  Expect overnight
lows to be near normal across much of the area, although north
Georgia my be just below normal Wednesday night into Thursday
morning.  Afternoon temperatures will moderate into the upper 50s
north to lower 70s southeast.

Atwell

LONG TERM /Thursday through Tuesday/...

Have made no changes to the long term. Models still on track for
low pressure developing in the Gulf during the Thursday/Friday
time frame. ECMWF still is farther south with the low than the GFS
and the the northern extent of the rain into the forecast area is
still the question. So for now the pops have not been changed. The
low pulls rapidly to the east and the remainder of the forecast
looks dry. However...another front drops into GA late Saturday
with an accompanying band of moisture which appears limited. So
have not added any pops for Saturday or Saturday night for now.
Previous discussion is included below.

41

PREV DISCUSSION... /Issued 302 AM EST Tue Nov 21 2017/

LONG TERM /Wednesday Night through Monday/...

Models in the long term continue to vary from run to run on the
evolution of Thanksgiving Day system but fortunately have more
agreement among themselves than at any point in the last several
days. Both indicate a developing area of low pressure by the start
of the extended period over the Gulf of Mexico. The GFS is
slightly stronger and further north with the system than the ECMWF
but overall deep moisture profiles are very similar with this run.
By Wed night, precipitable water values in excess of 1.4 inches
are moving into portions of Central GA in increasing favorable
isentropic upglide environment.

Given the good model agreement, will go with likely pops for the
extreme southern tier but give a sharp gradient to pops with less
than 20 for the Atlanta Metro. it should be noted though that it
would take very little in surface low displacement northward to
go from nothing to near washout for areas along I20 on
Thanksgiving.

Model differences continue through Friday with GFS faster with the
progression of low and ECMWF remaining displaced southward
although both models show a Florida peninsula track. This should
allow drier air to be drawn in on the north side of the system
Friday into the weekend effectively ending rain chances. Fairly
benign pattern thereafter with just a dry front to contend with
before high pressure builds in for the remainder of the period.

Deese


&&

.AVIATION...
00Z Update...
Scattered showers across the ATL/CSG are coming to an end. Rain
over south GA should stay out of the TAF sites. Cigs will slowly
fall through this evening, becoming IFR after 06Z most areas. Dry
air will spread rapidly into the forecast area Wednesday morning
making skies become VFR rapidly after sunrise. Winds will be light
to near calm tonight, becoming north northwest 8 to 10 kts
Wednesday.

//ATL Confidence...00Z Update...
Medium on cigs tonight.
High on remaining elements.

17

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          47  67  41  56 /  10   5   5  10
Atlanta         47  62  42  58 /  30   5   5   5
Blairsville     41  59  33  55 /  30   0   0   0
Cartersville    41  59  36  58 /  30   0   5   0
Columbus        49  67  47  62 /  30   5  10  10
Gainesville     45  62  40  55 /  30   5   5   5
Macon           50  70  47  59 /  20   5  20  30
Rome            40  58  34  58 /  10   0   5   0
Peachtree City  44  63  41  60 /  30   5   5   5
Vidalia         55  70  49  58 /  20  10  40  60

&&

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

$$

SHORT TERM...17
LONG TERM....20
AVIATION...17



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