Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 282313
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
713 PM EDT Fri Apr 28 2017



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

&&

.PREV DISCUSSION... /Issued 331 PM EDT Fri Apr 28 2017/

SHORT TERM /Tonight through Saturday Night/...

After this morning`s low clouds burned off, today has been
characterized by warm and dry conditions. The potential for any
precipitation is very limited for the remainder of the day.
Overnight low temperatures will be quite warm for this
time of year, only dropping to the upper 60s to near 70 by
Saturday morning. These values are about 10 to 15 degrees above
normal for late April.

The very warm trend continues on Saturday with forecast high
temperatures within a degree or two of record values at area climate
sites. Our area will be on the western periphery of a surface high
off the Atlantic coast, which will allow for some moisture
return. This moisture combined with plenty of heat and instability
will likely yield isolated to widely scattered thunderstorm activity
by Saturday afternoon, especially of the upslope variety in the
north Georgia mountains, though some isolated activity is possible
farther to the south as well. While overall thunderstorm coverage
should remain relatively limited, a few strong or severe
thunderstorms will be possible given ample forecast instability
around 3000 J/kg in north Georgia as well as relatively steep lapse
rates of 6.5 - 7 C/km. Strong winds and hail would be the primary
threats in these pulse thunderstorms Saturday afternoon.

Thunderstorm activity should begin to diminish after
sunset Saturday with continuing above average temperatures Saturday
night.

RW

LONG TERM /Sunday through Friday/...

Models are still in fairly good agreement in the long term.

Sunday will be warm across much of north/central GA. Anticipate the
typical diurnal thunderstorms Sunday afternoon with the best
coverage across the higher elevations.

The next storm system looks to approach the NW tier of GA just prior
to sunrise and slowly move east across the area through Monday
afternoon. The overall extent of severe weather looks somewhat
marginal across north GA and possibly a bit better organized
further south. While the upper level support is displaced to the
north, the better instability collocated with low/mid level shear
and high values of helicity is noted further across central GA.
Given the timing of fropa and cloud coverage ahead of this system,
not sure how much instability will be realized. But for locations
that are not observing as much cloud coverage during the morning
hours (perhaps those across central and eastern GA), this area may
see a bit more activity, especially during the afternoon hours.
The shear and helicity are the best ingredients with this system
at this point, so anticipate a HSLC possible QLCS scenario for
Monday. Given we are within the spring months and models tend to
downplay instability, we will have to keep a close eye on this
storm system and see how it evolves through the weekend.

Anticipate a reprieve after the aforementioned front exits late
Monday through Wednesday with the typical diurnal thunderstorms
during the Wednesday afternoon. The next system may be long-
winded as we tap into moisture riding the southern stream starting
Wednesday night. Meanwhile a deepening trough will dip south and
pivot through the area with a closed low slowly tracking northeast
Friday into Saturday. This may mean a prolonged rain event with
instability in question. The severe potential during this period
will ultimately depend on the surface low placement and upper
level dynamics. At this point, it is too hard to narrow down the
fine details. However, it is safe to say that the end of the
work-week into the weekend looks anomalously wet.

26

PREV DISCUSSION... /Issued 348 AM EDT Fri Apr 28 2017/

LONG TERM /Saturday Night through Thursday/...

Medium range models in relatively good agreement through the period,
at least with respect to the large-scale patterns. Two main focal
points for organized, widespread, beneficial precipitation centered
on late Sunday/early Monday and again late in the work week.

System moving in late Sunday still showing some potential for strong
to severe thunderstorms. Models continue to weaken the instability as
the system moves across, but also continue to show a decent shot of
low-level and deeper-layer shear. These elements still not aligning
all that great but they do merit watching closely. Timing is a little
later than previous runs with best forcing/instability/shear not
pushing into the far west until closer to 12Z Monday.

Late week system also showing up currently as somewhat lacking in
instability, but this is quite a ways out in the model run and the
surface and upper-level forcing are showing enough potential to keep
an eye on this system as well.

Time periods between these systems show a general flow pattern
supporting some isolated to scattered, mainly diurnal, convection
possible.

20


CLIMATE...

Records for 04-29

               Max Temperature         Min Temperature
  Station      High        Low         High        Low
  -------  ----------  ----------  ----------  ----------
   KAHN      90 1915     50 1999     66 1975     38 1973
                                        1970        1928
   KATL      88 1894     47 1934     67 2014     39 1992
                                        1989
                                        1970
   KCSG      92 1943     57 1934     71 1970     39 1928
                1927
   KMCN      92 2012     50 1934     68 1970     37 1992
                                        1914
                                        1912

&&

.AVIATION...
00Z Update...
No major changes from the previous forecast. Mostly VFR conditions
through the forecast. With mostly clear skies tonight and light
winds, patchy fog could develop and have added that to most of the
TAFs. Winds will become southeast 5 to 10kts with a few gusts.
Other concern is the smoke from the southeast GA fires. As the
winds turn southeast late tonight/Saturday, some of the smoke
could spread into the MCN and ATL area. At this time will leave it
out of the TAF due to uncertainty but this will need to be
watched.

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

17

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          67  89  66  85 /   5  20  20  10
Atlanta         69  87  69  85 /   5  20  10  10
Blairsville     63  84  63  78 /  10  30  30  20
Cartersville    67  88  67  85 /  10  20  10  10
Columbus        70  89  69  87 /   5  20  10   5
Gainesville     66  86  66  82 /  10  30  20  20
Macon           67  90  67  89 /   5  10   5   5
Rome            67  89  67  86 /  10  20  10  10
Peachtree City  66  87  66  85 /   5  20  10  10
Vidalia         70  91  68  89 /   5  10   0   5

&&

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

$$

SHORT TERM...17
LONG TERM....31
AVIATION...17



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