Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
641 am EST Friday Dec 19 2014
Previous discussion... /issued 353 am EST Friday Dec 19 2014/
Short term /today through Saturday/...
current satellite loop shows main low center spinning just north
of the New England states. There is also a large moisture plume
extending from this low out across the western Atlantic...over
central Florida...across the northern Gulf...through Mexico...and
out into the Pacific. You can also see a developing wave along
this plume now over New Mexico and western Texas which will become
the next weather make for Georgia. This developing wave is expected to
move east out of Texas and across the Gulf Coast states today. This
wave will begin to spread precipitation across Georgia by 00-06z Sat.
The models are in good agreement showing strong isentropic lift
from the southwest by this afternoon/early evening...overspreading
majority of area after midnight. Have continued with probability of precipitation
increasing from the SW beginning around 18z today maxing out after
midnight. Keep probability of precipitation high through tonight and begin diminishing
from the northwest Sat morning through Sat night. Quantitative precipitation forecast values still do not
look that impressive with storm totals generally less than a half
Long term /Saturday night through Thursday/...
model solutions continue to show an active weather pattern in the
long term... with GFS and European model (ecmwf) showing another cool wedge
setting up on Sunday and getting overrun with a moist middle level
southerly flow. This gets enhanced by a series of weak
disturbances in the southwest flow aloft and should result in
areas of mainly rain spreading over the area Sunday afternoon and
Sunday night. The Wedge appears to hold strong Monday and Monday
night as disturbances continue to traverse the state and warrant a
chance of rain for most areas through Monday night. At this
time... instabilities and any thunder threat appears to remain
mainly across south Georgia Monday-Monday night. However... this
changes Tuesday and Tuesday night as models agree on a long wave
trough deepening over the plains on Tuesday... then kicking east
Tuesday night and dragging a cold front across the area Tuesday
night-Wednesday morning. Ahead of the approaching trough and
associated cold front... European model (ecmwf) and GFS are showing 200-600 MUCAPE
nosing up across mainly central Georgia Tuesday afternoon and evening.
This coupled with moderate deep layer shear and strong diffluent
flow aloft will warrant adding mention of isolated thunderstorms
across much of central Georgia Tuesday afternoon and evening... but
suspect the thunderstorm threat could spread into parts of north
Georgia with later model runs considering the expected upper
forcing. Still much uncertainty on any severe storm threat as
instabilities and deep shear remain fairly modest for now... but
will continue to monitor for this potential... especially across
parts of central Georgia where the greater instabilities and shear
are expected. Behind the cold front... wrap around moisture...
strong upper forcing and temperatures dropping into the middle 30s suggest
the potential for a few snow showers across mainly northeast
Georgia Wednesday morning... but no significant accumulations are
expected with air and ground temperatures above freezing. The snow
showers potential returns Wednesday night-Thursday morning... but
with much less available moisture to work with. Otherwise...
expect high pressure and a dry air mass to dominate mostly on
not much change from the 06z taf set. VFR conditions to start
this taf period but ceilings will lower as precipitation moves in after
00z Sat. Currently high clouds across the area but ceilings will
increase and lower through the day. By 06z Sat looking for
ceilings in the 3000-4000ft range with showers moving across the
taf sites. This precipitation will continue through Sat ending Sat
afternoon. Winds are out of the northwest but will turn to the NE by 00z
and to the east by 06z. Winds speeds expected to stay 10kt or
less. Visibilities not expected to be an issue but could briefly see some
MVFR visibilities in and around any stronger showers over night.
//Atl confidence...12z update...
medium to high.
Preliminary point temps/pops...
Athens 55 41 47 39 / 10 100 100 20
Atlanta 54 42 50 42 / 20 100 100 10
Blairsville 51 38 46 37 / 5 90 80 5
Cartersville 51 38 49 38 / 20 100 100 10
Columbus 58 45 56 44 / 50 100 100 20
Gainesville 51 40 47 39 / 10 100 100 10
Macon 59 43 55 42 / 40 100 100 20
Rome 51 37 50 36 / 10 90 80 5
Peachtree City 54 40 51 37 / 30 100 100 20
Vidalia 62 47 56 45 / 20 100 100 20