Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 220154 AAB
AFDFFC

Area Forecast Discussion...UPDATED
National Weather Service Peachtree City GA
954 PM EDT Fri Jul 21 2017

.UPDATE...

Stretched the POPs a little later into the evening across the
southern counties as some outflow-driven convection persists.
Otherwise just made a few minor tweaks to hourly temps/dewpoints,
etc. to account for evening trends. General arc of the short-term
forecast grids remains on track.

20


&&

.PREV DISCUSSION... /Issued 745 PM EDT Fri Jul 21 2017/

SHORT TERM /Tonight through Saturday Night/...

The upper low that was over north Florida/South Georgia is forecast
to fill tonight leaving a weak ridge of high pressure over the
Tennessee Valley. The ridge of high pressure is not strong enough to
suppress completely the diurnal convection across the CWA this
afternoon. The ridge will remain in place Saturday with a weak
trough of low pressure across central/south Georgia. A little more
Gulf moisture will move into the forecast area Saturday with
southwest winds and this will create a more scattered nature to the
thunderstorms than isolated and have therefore keep chance pops
going across north and parts of central GA.

The big story continues to be the heat. MOS Guidance temperatures
have been running a degree or two too cool for max temps across much
of the area and have made adjustments to max temps for Saturday
which is pretty close to persistence. Adding slightly higher
dewpoints Saturday will produce heat index values of 105 to 108
across parts of central Georgia. Have therefore issued a Heat
Advisory for areas along and south of a Columbus to Macon to
Louisville line for Saturday afternoon.

17

LONG TERM /Sunday through Friday/...

Guidance still in line for more active pattern and scattered to
numerous convection each day given moist/unstable regime. Still
looking to have some forcing mechanisms beyond the diurnal
component in the form of an early week front approaching the area
Monday, stalling into midweek, and then late week transition to
more NW flow aloft, which would make the area more susceptible to
shortwave impulses and possibly some rounds of more organized
storms to the north. Have raised some late week pops accordingly.
Otherwise forecast on track and did refresh of overall model
blend. Previous discussion follows...

Baker

PREV DISCUSSION... /Issued 730 AM EDT Fri Jul 21 2017/

LONG TERM /Saturday Night through Thursday/...

The extended period will be characterized by increasing rain chances
as the upper trough pushes into the eastern US from Sunday into
early next week. This upper level troughing in concert with abundant
moisture will bring largely diurnal showers and thunderstorms each
afternoon. Additionally, a weak cold front will be pushed southward
into the region by Monday in to Tuesday which will serve as a
further focus for convective development. This boundary will linger
into midweek, so climatologically typical diurnal showers and
thunderstorms will be the rule during this time frame. As is also
typical for late July in Georgia, some thunderstorms may become
strong during the afternoon and evening hours during the hours of
peak instability.

One positive aspect of the increased rain chances will be increased
cloud cover which will bring lower afternoon high temperatures as
compared to the last few days. Nonetheless, with dewpoints
remaining in the 70s, it will still feel warm and muggy.

RW

AVIATION...
00Z Update...

VFR conditions currently predominate across the forecast area.
Should see scattered MVFR or lower visibilities developing by 03-
06Z. Coverage of MVFR or lower visibilities expands 06Z through 12Z,
however right now I think most TAF sites remain VFR. Isolated to
scattered convection is concentrated mainly south of the TAF sites
this evening and should continue to slowly diminish through 06Z.
Isolated to scattered convection fires back tomorrow afternoon,
generally 18-00Z, however, coverage not high enough to include a
PROB30 for thunder. Winds will be light southwest through the
forecast.

//ATL Confidence...00Z Update...

High on all elements.

20

CLIMATE...

Records for 07-21

               Max Temperature         Min Temperature
  Station      High        Low         High        Low
  -------  ----------  ----------  ----------  ----------
   KAHN     108 1926     78 1938     76 1993     60 1929
                                        1926
   KATL     102 1986     76 1920     80 1881     61 1929
                            1899
   KCSG     103 1942     80 2014     78 2015     61 2009
                                        1996
                                        1986
   KMCN     106 1986     78 1929     78 2015     64 1910
                                        1954
                                        1934

Records for 07-22

               Max Temperature         Min Temperature
  Station      High        Low         High        Low
  -------  ----------  ----------  ----------  ----------
   KAHN     103 1932     72 1970     76 1930     58 1947
   KATL     102 1993     75 1970     80 1881     59 1947
   KCSG     102 1943     80 1970     79 1934     61 1922
   KMCN     102 1983     81 1913     79 1983     61 1947
                1977

Records for 07-23

               Max Temperature         Min Temperature
  Station      High        Low         High        Low
  -------  ----------  ----------  ----------  ----------
   KAHN     104 1924     73 1904     79 1983     60 1966
   KATL     100 1952     76 1890     78 1943     60 1947
   KCSG     103 1952     79 1913     80 1983     63 1947
                1943
   KMCN     102 1987     75 1919     79 1983     62 1966
                1952                                1947
                1907

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          72  96  73  93 /  20  30  20  40
Atlanta         75  94  76  91 /  20  30  20  50
Blairsville     68  89  69  86 /  20  40  20  50
Cartersville    72  93  72  91 /  20  30  20  50
Columbus        76  96  77  92 /  30  30  20  40
Gainesville     72  93  73  90 /  20  30  20  50
Macon           72  97  73  93 /  30  20  20  40
Rome            73  94  73  92 /  20  30  20  50
Peachtree City  73  93  73  91 /  20  30  20  40
Vidalia         73  95  74  93 /  30  20  20  30

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon to 6 PM EDT Saturday for the following
zones: Bibb...Bleckley...Chattahoochee...Crawford...Crisp...
Dodge...Dooly...Emanuel...Houston...Jefferson...Johnson...
Laurens...Macon...Marion...Montgomery...Muscogee...Peach...
Pulaski...Schley...Stewart...Sumter...Talbot...Taylor...
Telfair...Toombs...Treutlen...Twiggs...Washington...Webster...
Wheeler...Wilcox...Wilkinson.

&&

$$

SHORT TERM...20
LONG TERM....26
AVIATION...20


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