FXUS62 KFFC 190840

Area Forecast Discussion
National Weather Service Peachtree City GA
440 AM EDT Mon Mar 19 2018

.SHORT TERM /Today through Tuesday/...
Primary concern is timing and intensity of severe convection. 00Z
and more recent model guidance continue to indicate favorable
parameters for supercells with large hail and a few tornadoes this
afternoon and evening with development of a line of strong/severe
storms after 10pm over NW GA moving SE into ATL metro after
midnight before weakening and perhaps dissipating. Hires models
still not solid on most likely locations of supercells during the
afternoon. Could be a cluster over northern AL and southern TN
moving into northern 1/4th of GA and another cluster over
eastcentral AL and westcentral GA moving into middle GA but our
confidence remains low. Ingredients for supercells will be in
place across all of CWA with MLCAPE ranging from 2000 J/kg over
westcentral GA to 250-500 J/kg over NE GA in area of retreating
CAD air mass. 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. As
mentioned night before, 0-1km shear in this range could be keep
tornado threat confined to weaker, shorter-lived supercell-based
tornadoes. Significant tornado parameter (STP) values from GFS
coming up to 4-7 over AL/GA border SW of ATL metro, but keep in
mind forecast values typically larger than observed (i.e. SPC RAP
analysis) STP so observed STP values of 2-3 are likely what we
will end up with.

Supercell threat will diminish greatly after 10p with line of
storms expected afterward. However with diminishing low level
convergence, large scale lift and MLCAPE, even this line should
weaken and eventually dissipate by 1-2a.

Could see storms refire over far SE counties Tuesday midday and
early afternoon, however parameters for severe storm not as
favorable. One or two storms could be strong to severe with large
hail possible.


.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



06Z Update...
MVFR cigs expected to develop by 09-10Z and IFR by 12-13Z before
improving back to MVFR by 16-17Z. Any chc for TSRA should hold off
until 21Z and may be scattered in nature such that probabilities
remain low enough to keep probs at TEMPO or lower. After 02Z, line
of TSRA will likely affect ATL metro airports but should move out
or dissipate by 06-07Z. KMCN and KCSG should not be affected by
this line. SE sfc winds will become SW as line of storms moves
thru 03-07Z.

//ATL Confidence...06Z Update...
Medium on TSRA likelihood this afternoon
Medium confidence in IFR duration this morning
High confidence on all other elements



Athens 65 56 71 39 / 60 80 40 40
Atlanta 68 57 68 37 / 50 70 40 30
Blairsville 59 49 62 33 / 60 80 50 50
Cartersville 68 53 65 36 / 60 80 50 30
Columbus 75 61 70 41 / 50 50 30 20
Gainesville 61 53 67 36 / 60 80 40 50
Macon 74 62 75 40 / 50 60 40 20
Rome 68 53 63 36 / 60 80 40 40
Peachtree City 71 57 69 39 / 50 70 40 30
Vidalia 75 64 76 46 / 60 50 60 10




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