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Office: FFC

FXUS62 KFFC 180213

Area Forecast Discussion
National Weather Service Peachtree City GA
1013 PM EDT Sat Mar 17 2018

Wound up being an interesting evening for the CWA as several
strong to severe thunderstorms affected portions of north and
central Georgia. The strongest storms clipped the far northeast
Georgia counties...within a conducive environment for large hail
and rotating updrafts. Given lack of sufficient lower level radar
data given radar void across this confirmed reports of
tornadic touchdown across these areas have been noted...tho did
receive some half dollar size hail reports. Although these storms
are still moving across northeast Georgia and are still
severe...they have moved out of the CWA and no additional severe
activity is expected through tonight for our local area.

Earlier thunderstorm activity was associated with large scale
lift courtesy of a shortwave trough moving swifting south within
the Ohio Valley along with its southward moving sfc cold frontal
boundary. Both the shortwave and cold front will continue to
approach the area through the overnight hours. Really only
anticipating some cloud cover with this fropa and no real change
in airmass is forecast...tho could see slightly lower PW and
mixing ratio values across north and east Georgia thru Sunday

Forecast seems to be in good shape this evening. Have made only
minor tweaks to the grids the last few hours. Do expect an overall
pleasant day on Sunday...with showers and storms approaching from
the west by late afternoon. Severe parameters are not expected to
quite come together with this initial round of precip as of right
now thru Sunday evening...tho still looking like a different story
for Monday.



.PREV DISCUSSION... /Issued 744 PM EDT Sat Mar 17 2018/

PREV DISCUSSION... /Issued 248 PM EDT Sat Mar 17 2018/

SHORT TERM /Tonight through Sunday Night/...
Most of the showers have dissipated with a few remaining across
central GA. These showers will continue shifting south and should be
out of the CWA by 00Z. A weak short wave an associated cold front
will move across the Tennessee Vally this evening. This could tap
into some low level moisture as it move into the region bringing a
chance of showers/tstorms to extreme northeast Georgia this
evening/tonight. The cold front will move into central/south GA
Sunday, however as the next short wave moves into the Mississippi
Valley, the front will move north as a warm front. Significant
isentropic lift along the warm front will bring increasing chance of
showers and thunderstorms to the western part of the CWA late Sunday
afternoon and across the entire CWA Sunday night.


LONG TERM /Monday through Saturday/...
Mainly only tweaks to the long term based on the latest
guidance. A wet and stormy period is still expected Monday
into early Tuesday.


A fairly aggressive system making its way into our area for the
beginning of the extended forecast. High pressure builds back
into the region for the middle to end of the 7 day forecast.

The cold front that moves through the area today moves back
northward as a warm front Sunday night with the next cold front
directly on its heels. Beginning Sunday night/Monday morning,
moist southwesterly flow sets up across the area as the warm
front moves into central portions of the state. Instability
indices increase across the state as a a strong piece of southern
stream energy interacts with the warm front. This will produce
periods of locally heavy rainfall and some isolated to scattered
thunderstorms. Currently, the axis of heaviest rainfall is progged
to be across central and south GA. Another bout of moderate to
locally heavy rainfall is possible Monday night into Tuesday as
the cold front moves through.

As far a s the possible severe weather from this system the
models are coming into a bit of better agreement as far as timing
and intensity. Instability peaks Sunday evening then weakens
Sunday night through early Monday morning. This should keep any
thunderstorms to a minimum but would not be surprised to see
strong thunderstorm during this time frame. The mid level lapse
rates stay fairly steep...and some surface instability will be
present so can not rule out a severe storm. Instabilities
increase during the day Monday with muCAPE increasing into the
800-1800j/kg range and shear and lapse rate values staying up as
well. There is not as much deep moisture present but with a
secondary cold front sweeping around the parent low and daytime
high temps in the 60s and 70s...the atmosphere will be primed for
severe storms to develop. SPC also agrees and has placed the
majority of the state under a slight risk for day 3 with NW and
west central GA under a 10 percent hatched area for significant
severe weather. Will be keeping a close eye on this over the next
few days

Behind the cold front, for the latter half of the week, colder than
normal temps will return. will most likely have to issues some
frost/freeze products Wed/Thu.


00Z Update...
Mainly passing cirrus expected thru this evening. Main question is
to what extent and how far north potential MVFR ceilings will get
across the TAF sites overnight. Given location of best
moisture/precip...think MCN and CSG will have best chance for MVFR
cigs with also some potential for fog and reduced vsbys. Further
north across metro ATL and AHN there could be some scattered to
perhaps BKN MVFR for a few hours but confidence is not high.
Patchy fog will also be possible across northern sites but not
thinking enough coverage or duration for vsby impacts. Showers and
storms should remain outside of airport locations thru Sunday
morning. Will see coverage increase from the west by late Sunday
afternoon. West winds will continue at less than 10kts.

//ATL Confidence...00Z Update...
Low confidence on potential MVFR cigs overnight.
High on all other elements.



Athens          77  54  74  53 /  40   5  10  80
Atlanta         74  55  73  55 /  80   5  20  80
Blairsville     70  46  68  48 /  70  60   5  70
Cartersville    73  51  71  53 /  80  10  20  80
Columbus        81  60  78  60 /  60  10  50  90
Gainesville     72  53  71  52 /  80  10   5  80
Macon           79  58  78  57 /  60  10  30  80
Rome            75  50  71  53 /  70  10  10  80
Peachtree City  74  55  74  56 /  80   5  30  90
Vidalia         79  61  79  60 /  60  30   5  80