Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 270911
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
511 AM EDT Tue Jul 27 2021


...Morning Area Forecast Discussion...

.SHORT TERM /Today through Wednesday/...
The word that comes to mid is `gross` when looking at the short term
forecast. Dewpoints have already risen into the low 70s, but by this
afternoon are expected to rise into the mid to upper 70s as some
areas already experienced yesterday. With highs generally in the low
to mid 90s, these dewpoints will push Heat Indices into the triple
digits for the 2nd or 3rd straight day (depending on location).
Several areas could even experience apparent temperatures near or
above 105 degrees which has prompted a Heat Advisory primarily for
portions of Central Georgia, though we wouldn`t be surprised to see
a few scattered spots of 105 Heat index values in and around the ATL
metro and in areas of NW GA.

Synoptically, the high amplitude blocking ridge over the western and
central CONUS will continue to grow stronger with a mid-level ridge
extending latitudinally into the Tennessee River Valley today and
then into Georgia by tomorrow. Near the surface, a high pressure
over the midwest is pushing and squeezing extra moisture into the
Southeast where ample Gulf moisture already continues to linger
already and a weak surface low hangs onto the GA coastline. these
effects will push PWATs well above 2 inches for the entire forecast
area outside of the mountains. And with an extra push of surface
forcing from a stalled and dissipating frontal boundary across
Tennessee, we`re likely to see numerous showers and thunderstorms
across the forecast area this afternoon and evening, possibly
lingering past midnight for portions of Central Georgia.

By Wednesday, the a bit of the high pressure airmass will attempt to
bleed into the forecast area, lowering PWATS due to slightly drier
air in the mid-levels but doing little near the ground. In fact,
dewpoints are expected to decrease by only a few degrees but the
lowered surface moisture will begin to decease the destabilizing
acts of convection which will push afternoon temperatures for north
Georgia into the mid 90s, keeping heat indices reaching the triple
digits once again.

Thiem


.LONG TERM /Wednesday Night through Monday/...
Main forecast concern in the long term period is extreme heat
Thursday-Friday.

Bulk of 00Z guidance suite still indicates that upper ridge over the
western and central CONUS will continue to build east into the SE
states Thurs-Fri before westerlies and associated baroclinic zone on
periphery of upper eastern CONUS dips further south into the region
this weekend. Extreme heat with apparent temps (heat index) in the
105-110 range have been observed over the mid-south last two days,
so confidence increasing further for a potentially significant
heat event Thurs- Fri with apparent temps 103-108 over all of CWA
except for mountain areas. NBM T guidance was adjusted up a degree
for Thursday and unchanged for Friday, but will need to monitor
observed biases next two days and be ready to adjust as needed.

As far as rain chances and the forecast beyond Friday, afore-
mentioned front should push into the state this weekend but no
significant cooler/drier air behind it. Increased clouds and SHRA/
TSRA coverage will help knock temps down and minimize extreme
heat threat. As upper trough amplifies while remaining stationary
through the middle of next week, wet pattern with more normal
temps and mainly diurnal afternoon/evening convection. Heavy rain
not anticipated but could change as model forecasts get closer to
the event early next week.

Tropical activity not expected in the western Atlantic basin
through at least Saturday.

Previous long-term discussion follows...

SNELSON

PREV DISCUSSION... /Issued 311 PM EDT Mon Jul 26 2021/

LONG TERM /Wednesday through Monday/...

Apparent Temperatures (Heat Index Values) may approach 105 degrees
for the southern half of the CWA for the end of the week into the
weekend.

CWA remains in NW flow through much of the extended period of the
forecast. Longwave trough that sets up just to the east looks to
retrograde a bit by early next week, driving the ridge back to the
west. At the surface, there should be a weak frontal boundary across
northern GA Wednesday into Thursday. This front should become
diffuse by early Friday. A second frontal boundary should begin to
sag southward across northern portions of the state by the weekend.
This front will remain stationary through early next week.

Widespread heat index values may approach 105 degrees south of the
Interstate 20 corridor Thursday and Friday. With the stationary
frontal boundary setting up across northern GA for the weekend, the
highest heat index values will likely shift south of an Athens to
Macon to Columbus line.

NListemaa

SNELSON


&&

.AVIATION...
12Z Update...
VFR conditions for now, but widespread patchy BR/FG once again
expected with MVFR/IFR VSBY restrictions between 9-14Z, with
chances for lowered values where heavy rain fell yesterday
evening. Guidance generally favoring NW winds on Tuesday but
could be variable through the morning and afternoon at 4-7 kts.
Expecting scattered to numerous showers and thunderstorms on
Tuesday afternoon/evening, so am maintaining the PROB30 starting
at 18z Tuesday for ATL and other metro sites.


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

Thiem


&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          92  72  93  73 /  70  60  20   5
Atlanta         92  73  93  73 /  60  50  30   5
Blairsville     86  66  89  66 /  70  50  20   5
Cartersville    93  72  94  72 /  60  50  20   5
Columbus        95  74  93  74 /  70  60  50  10
Gainesville     90  71  93  73 /  70  50  20   5
Macon           96  73  93  73 /  70  60  50  10
Rome            93  73  95  72 /  60  40  10   5
Peachtree City  93  72  93  73 /  60  50  30   5
Vidalia         92  74  91  74 /  70  70  60  20

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 8 PM EDT this evening for the
following zones: Baldwin...Bibb...Bleckley...Butts...
Chattahoochee...Crawford...Crisp...Dodge...Dooly...Greene...
Hancock...Houston...Jasper...Johnson...Jones...Lamar...Laurens...
Macon...Marion...Monroe...Montgomery...Morgan...Muscogee...
Newton...Oconee...Peach...Pulaski...Putnam...Schley...Stewart...
Sumter...Talbot...Taylor...Telfair...Treutlen...Twiggs...Upson...
Walton...Washington...Webster...Wheeler...Wilcox...Wilkinson.

&&

$$

SHORT TERM...Thiem
LONG TERM....SNELSON
AVIATION...Thiem


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