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FXUS62 KFFC 172315
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
715 PM EDT Tue Jul 17 2018



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

&&

.PREV DISCUSSION... /Issued 335 PM EDT Tue Jul 17 2018/

SHORT TERM /Tonight through Wednesday Night/...

The forecast area remains under a general northwest flow through
the short term. Models are consistent with a front pushing into
north GA late tonight and early Wednesday...and a weak low forming
on the front over central GA. Drier air gradually spreads into
north GA during this time as forecast soundings show PW values
decreasing steadily through Wednesday evening. Have continued
with diminishing pops overnight tonight and leaving them out
altogether across the far north tomorrow and tomorrow night.
Instability should be better with deeper moisture continuing for
central GA...so have left pops in for that area through the
period.

41

LONG TERM /Thursday through Tuesday/...

Model guidance is in agreement that an elongated frontal system
stretched through central/southern Georgia will start off the long
term period on Thursday morning, with enough forcing to focus
thunderstorm development in the southern half of the state.
Differences in the spatial coverage of these storms will be the
biggest question regarding POPs on Thursday. Most models have a weak
low pressure forming along the baroclinic boundary, somewhere around
southern GA but only a few models, like the GFS, wraps enhanced
moisture around the northern side of the cyclone. this will most
likely be the difference between scattered showers/thunderstorms
or pleasant conditions for north GA on Thursday.

Friday, the forecast area gets back into a northwest flow pattern as
a strong mid-level low pressure system moves across the western
Great Lakes area. Along with it, a surface high pressure system off
the New England coast looks to enforce a weak wedge into the forecast
area. This effect should push most of the thunderstorm initiation
further south at the start of Friday, propagating outwards along
outflow boundaries from there. Furthermore, some models are showing
signs that an MCS may develop within the NW flow pattern and move
into NW GA by Thursday afternoon. With that said, models are
notoriously bad at handling NW flow MCSs over a day in advance, so
we will need to see how high-res models evolve this potential system
closer to Thursday night/Friday morning.

Saturday looks to be the best day for severe chances as of right
now. The mid-level low pressure system near the Great lakes will
continue to move eastward with a mid-level trough access stretching
down into the Carolinas. Both the GFS and the Euro have a shortwave
trough moving through GA. The enhanced shear and forcing given from
the shortwave offer the best chances for organized severe convection
we`ve had in several weeks. Afterwards, models diverge with the
evolution of the longwave trough over the area. The Euro teases
pleasant summertime conditions with limited precip and drier air,
the GFS keeps the mid-level low just north of the area enhancing
diurnal showers through the beginning of next week.

22

PREV LONG TERM DISCUSSION... /Issued 337 AM EDT Tue Jul 17 2018/

LONG TERM /Wednesday Night through Monday/...

Beginning of the extended forecast sees moisture returning northward
across the region. Upper-level flow continues to amplify as the
eastern U.S. upper trough deepens. Good short wave energy in the
northwesterly flow drives another sharp surface frontal boundary into
the forecast area Saturday. Combined with moderate instability and
mid-level winds, the threat for at least slightly more organized
strong to severe storms cannot be ignored. By the beginning of next
week, the upper flow begins de-amplifying some as the eastern trough
lifts and the western ridge builds back toward the region. not seeing
enough to eliminate POPs, but we are likely to see less coverage and
a return to a more diurnal convective cycle.

20


&&

.AVIATION...
00Z Update...
Convection will dissipate this evening. A cold front will drift
into north GA tonight and slowly push into central Georgia
Wednesday. This will keep most of the convection over CSG/MCN
Wednesday afternoon. Not out of the question for an isolated TSRA
in the ATL/AHN areas. MVFR cigs will spread into central Georgia
late tonight. Cu field will develop late Wednesday morning and
continue into the afternoon.

//ATL Confidence...00Z Update...
Medium on showers this evening.
Medium on convection Wednesday after 18Z.
High on remaining elements.


17

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          72  91  72  88 /  30  20  20  30
Atlanta         73  91  73  89 /  30  20  10  30
Blairsville     65  85  64  83 /  30  10  10  30
Cartersville    71  90  69  90 /  40  10  10  30
Columbus        75  93  74  93 /  40  50  20  40
Gainesville     71  89  71  87 /  30  20  10  30
Macon           74  92  73  90 /  40  50  30  40
Rome            71  91  68  91 /  40  10  10  20
Peachtree City  72  92  71  90 /  30  20  20  30
Vidalia         75  91  74  89 /  40  60  40  60

&&

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

$$

SHORT TERM...17
LONG TERM....Reaves
AVIATION...17

NWS FFC Office Area Forecast Discussion