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Area Forecast Discussion (AFD)

Issued by Peachtree City, GA (FFC)

FXUS62 KFFC 200438

Area Forecast Discussion
National Weather Service Peachtree City GA
1238 AM EDT Tue Mar 20 2018

Severe weather threat has ended across portions of the NW metro.
Have extended the watch a tier of counties southward. Tweaked pops
to reflect current trends. Otherwise, no changes. 


.PREV DISCUSSION... /Issued 919 PM EDT Mon Mar 19 2018/ 

The potential for severe weather continues across portions of the
CWFA into early Tuesday morning. Have only made a few tweaks to
the forecast, mainly for precip timing. 

However, the main change to the forecast was to add a Tornado
Watch for portions of north and central GA through 4am.

PREV DISCUSSION... /Issued 749 PM EDT Mon Mar 19 2018/ 

PREV DISCUSSION... /Issued 449 PM EDT Mon Mar 19 2018/ 

SHORT TERM /Tonight through Tuesday Night/...
An upper level low will deepen as it lifts into the TN valley 
tonight. the surface front will push through the forecast area 
through the day tomorrow. Pre-frontal convection - isolated 
thunderstorms will move into portions of west GA over the next 
hour, and increase in coverage through the evening hours. The 
atmosphere has destabilized with breaks in clouds over west and 
central GA. Ingredients for supercells will be in place across all
of CWA with MLCAPE of 1500-2500 J/kg across the area through this
evening. Vertical wind shear quite strong with 0-6km shear 
ranging from 50kts over middle GA to 75kts in the far north and 
0-1km shear 20kts over middle GA to 30kts in the far north. SPC 
has issued a Tornado Watch west of our forecast area, but with the
sounding profiles from the HI-RES guidance supporting supercell 
structures with strong rotating updrafts between 22z and 03z, 
expect watches to be issued later this evening. A second line of 
storms associated with the front will move across the state from 
NW to SE after midnight into tomorrow, with cells weakening as 
they get into central GA around daybreak, but while severe is not 
expected we could still see thunder through the early morning 
hours. Do mot expect as much clearing as models are advertising, 
based upon the proximity of the wrap around moisture and have held
onto clouds through the day tomorrow with some break across north
Georgia by afternoon. Guidance temperatures are close and have 
stayed close to a blend through the period. Temperatures will stay
nearly steady across northwest Georgia with a warm up over east 
central Georgia ahead of the cold air advection.


LONG TERM /Wednesday through Monday/...
Wrap around moisture will move across north Georgia Tuesday night
into Wednesday as the upper upper low shifts into the Carolinas.
Cooler temperatures behind the cold front will bring light
showers over north Georgia, along with a rain/snow mix and snow 
showers by morning over the higher elevations. Any accumulations
will be light at best. Otherwise extended forecast trends were
mostly unchanged. See previous forecast discussion below.


LONG TERM /Tuesday Night through Sunday/...
Much colder temperatures will be advecting into the area on breezy 
northwest winds by Tuesday night behind a cold front. As an upper 
low passes to the north Tuesday night into Wednesday morning, the 
chance for light showers will linger across primarily north Georgia. 
With temperatures dropping near or below freezing by Wednesday 
morning in far north Georgia, the likelihood for a transition to a 
rain/snow mix or light snow showers will increase. Light snow 
accumulations will be possible across the higher elevations by 
Wednesday morning. At this time, generally expecting only up to a 
around a half inch in these higher elevations. Any light snow 
accumulations would melt by midday Wednesday as temperatures warm 
well above freezing. Wednesday will remain a chilly day by late 
March standards with high temperatures largely in the 50s (and 40s 
in far north Georgia). Sustained northwest winds around 20 mph with 
higher gusts will add to the chill.

Thursday and Friday will bring moderating temperatures and will 
remain primarily dry with only a slight chance of a few showers 
sneaking into far north Georgia by late Friday. Rain chances appear 
to begin to increase more appreciably by Saturday as upper pattern 
transitions into a more zonal flow and a low pressure system moves 
into the Ohio Valley, though discrepancies remain with timing and 


18Z Update...
IFR or near IFR cigs will hold on over all TAF sites with a slow
improvement to MVFR between 20-22Z, just ahead of convection. 
Will see IFR set up after 00Z with a second round of thunderstorms
overnight between 04-11Z across all TAF sites, but mainly ATL 
area. Any TSRA will be scattered. SE-S winds will become SW as 
line of storms moves thru 03-07Z then become west and increase to 
10-15kts with gusts to 22-25kts after 15Z Tue. Expect variable 
winds with gusts with any thunderstorms.

//ATL Confidence...18Z Update...
Medium to low confidence in CIGs.
Medium confidence in timing of convection.
Medium to high confidence in all other elements. 


00Z Update...
IFR or near IFR cigs will hold on over ATL/AHN TAF sites with a 
slow improvement to MVFR through 08Z, just ahead of convection.
CSG and MCN will have MVFR/VFR CIGs until line of convection
arrives. Will see another round of thunderstorms overnight 
between 04-10Z across all TAF sites, but mainly ATL area. Any 
TSRA will be scattered. SW winds will become gusty with any storms
and shift to W behind the front with gusty winds throughout the
day on Tuesday.

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

Medium to low confidence in CIGs.
Medium confidence in timing of convection.
Medium to high confidence in all other elements.



Athens          39  54  34  60 /  20   5   0   0 
Atlanta         37  52  35  58 /  30   5   0   0 
Blairsville     33  42  28  51 /  50  30  10   0 
Cartersville    36  52  32  58 /  30   5   0   0 
Columbus        40  59  37  64 /  20   0   0   0 
Gainesville     36  50  33  56 /  30  10   0   0 
Macon           40  60  36  62 /  10   0   0   0 
Rome            35  52  32  58 /  40   5   0   0 
Peachtree City  38  55  34  60 /  30   0   0   0 
Vidalia         44  61  39  63 /  10   5   0   0 


Tornado Watch until 4 AM EDT early this morning for the 
following zones: Baldwin...Bibb...Butts...Clarke...Clayton...