Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
729 am EDT Sat may 30 2015
Previous discussion... /issued 349 am EDT Sat may 30 2015/
Short term /today through Sunday/...
models are mostly in agreement through the short term. Atlantic
moisture will continue to spread into south/central Georgia this
morning as seen with showers just off shore moving westward. A few
of these could make it into the extreme southeast/eastern parts of
the County Warning Area later this morning and afternoon. With daytime heating a
few storms could develop across northwest/north Georgia this afternoon.
The rest of the County Warning Area should be dry today. Models bring a short wave
into the County Warning Area late tonight and Sunday. This will increase
probability of precipitation...mainly after midnight and into Sunday. The best location
will be across north Georgia. Cape values increase to over 2600
and lapse rates increase to over 8 degrees. This will be enough
for some storms to be strong along with isolated severe possible
Sunday afternoon...mainly across north Georgia.
Long term /Sunday night through Friday/...
synopsis...00z GFS and European model (ecmwf) begin the period in good agreement
but once again diverge on the evolution of a cutoff low over the
gom/Gulf Coast states by middle week. Differences in the position of
the cutoff low make the forecast confidence fairly low for days 5
through 7 especially. Good news is both models are consistent in
developing much needed ridging over Texas and the central U.S.
Where an Arkansas is the preferred transportation method currently.
Interesting to note with the current mesoscale convective system over Texas at this time and the
associated vorticity maximum are what ultimately lead to the eventual cut
off low and our potential week long weather maker. However...the
GFS is currently doing a bit better with the position and track of
that system which lends itself to a potential better solution
downstream with the cut off low. Too early to tell at this point
but certainly something to watch.
Sunday night through Tuesday...fairly decent coverage of storms
expected Sunday night to start the period as a weak shortwave and
surface front move into the region. By Monday the mean 500mb trough
axis is centered over US with a weak surface front located across
central Georgia providing a focus for afternoon storms. With the lack of any
real suppression...afternoon storms will be prevalent each day. At
the same time per the GFS and GFS ensemble...cut off low taking
shape anywhere from central Gulf of Mexico to south Mississippi to
Florida Panhandle. European model (ecmwf) has trended a tad west from previous runs but
is still on the eastern edge of the model suite.
Wednesday through Friday...the cutoff low...where ever it ends
up...begins to tap into significant amounts of deep tropical
moisture from the northwest Carribean. Regardless of whether you
go with the European model (ecmwf) or GFS...they both agree on the deep moisture
tap by the low and begin to bring that moisture north on the east
side of the low...which is why it will be important to know where
the low eventually ends up. A western position will mean higher
probability of precipitation...more rain...and increased flood potential for US Wednesday
through Friday while a further east location will still mean a chance
of rain...but much lower overall chances and minimal flood threat.
Jury is still out on the eventual evolution of the low...but am
still leaning toward a more western position given the GFS
ensembles still favoring that solution...while not as far west as
runs 24 hours ago. Still maintaining afternoon probability of precipitation in the
forecast but one can expect these to change with time as we
resolve the upper low feature. At the surface...all models
including many ensemble members also hinting at a weak low within
the deep tropical plume that surges north. Again...upper low
position will determine the fate of such a feature if it occurs at
all. Given the upper low and its influence...any such feature
would be some sort of hybrid tropical system likely to remain
weak. Again...stay tuned to the forecast next week as its likely
to change and evolve with time.
VFR conditions through most of tonight. Expect MVFR ceilings to
develop around 09z sun and remain MVFR through Sunday morning.
It should remain dry today although isolated thunderstorms could develop north
and west of atl this afternoon. A storm system will bring
increasing chances of convection Sunday morning and have added
prob30 thunderstorms and rain to atl 17z sun. Winds will be southeast through
tonight...then become southwest after sunrise Sunday morning.
//Atl confidence...12z update...
medium on ceilings late tonight and Sunday.
Medium on timing of convection Sunday.
High on remaining elements.
Preliminary point temps/pops...
Athens 88 66 86 67 / 20 20 40 50
Atlanta 86 69 84 67 / 20 30 50 50
Blairsville 82 62 78 62 / 20 40 60 60
Cartersville 86 66 85 65 / 20 40 60 60
Columbus 89 68 89 69 / 10 20 30 30
Gainesville 85 66 83 66 / 20 20 50 50
Macon 90 66 89 68 / 20 20 30 30
Rome 87 66 84 65 / 20 40 60 60
Peachtree City 87 65 84 65 / 20 30 40 40
Vidalia 89 69 87 69 / 30 20 30 30