Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
956 PM EDT sun Oct 4 2015
Low pressure off the South Carolina coast continues to pump in
abundant low level moisture into the area. This continues to
result in areas of drizzle and occasional light rain. The showers
have been confined to the southeast corner of the forecast area
but have kept probability of precipitation high in all locations as event the drizzle will
measure at times. Otherwise...forecast in good shape and no
additional changes are planned.
Previous discussion... /issued 759 PM EDT sun Oct 4 2015/
Previous discussion... /issued 338 PM EDT sun Oct 4 2015/
Short term /tonight through Monday night/...
current radar loop still shows the main axis of precipitation
over SC with light showers streaming across east and central Georgia.
Current model runs seem to have a good handle on the situation
keeping that main moisture plume over the Carolinas through Monday
before pulling it off shore by 12z Tuesday as Joaquin pulls everything
NE and away from the coast. For the short term aspect we have
canceled the Flood Watch and eastern sections of the state should
only receive another half inch or less over the next 24 to 36
hours. Another issue we are dealing with are the strong winds
across NE Georgia. A nice little wave low center has developed along
the Georgia coast putting with a fairly tight pressure gradient over NE
Georgia this afternoon. This gradient is keeping winds blowing out of
the NE at 15-20kt gusting 25 to 35kt. This gradient should begin
to weaken this evening and the winds will also weaken through
tonight. With the very wet soils across that area we have been
receiving a lot of report of trees down so we will have to
continue to monitor this situation through Monday morning. Temperatures
will continue on the cool side with lows in the upper 50s and
lower 60s and highs mainly near 70.
Long term /Tuesday through Sunday/...
the blocking pattern will have broken down by Tuesday and become
more progressive through the long term period...resulting in a much
needed dry spell for the area.
Synoptic pattern to start the long term will feature low amplitude
ridge over central US caught between two closed lows in SW and off
the southern Atlantic coast. While main belt of westerlies
remains near US/Canada border. Stubborn low level moisture will
linger across eastern Georgia Tuesday morning as Atlantic plume
continues from cyclonic flow around closed low off Carolina coast.
This low will continue to migrate east as it becomes an open wave
over the Atlantic... allowing an 500 mb ridge centered over eastern
Mexico to begin to influence the southeast US. Synoptic subsidence
associated with this feature will allow for drying conditions as
the day progresses...further enhanced by surface high nudging into the
state from west to east. Expect this pattern to persist through Thursday
morning with none probability of precipitation.
Reinforcing Canadian surface high sliding across Great Lakes/northeast
will result in classical cad development by Thursday morning. With a
transition to weak zonal flow aloft and no significant moisture
return/fetch over the Gulf...expecting just some increase in cloud
A weak cold front will approach the area late Friday/Saturday. As it
does so...300k and 305k Theta sfcs suggest potential for weak
isentropic ascent across southern zones which may result in a few
light showers early Friday. Negligible MUCAPES suggest thunder
potential is minimal. Deterministic models are rather lackluster
with moisture during frontal passage. Have therefore held onto just a slight
chance probability of precipitation across north Georgia for now.
Models begin to diverge late in the period with respect to a closed
low across northern Mexico. European model (ecmwf) cuts this low off of the main flow
while the GFS lifts it into an open wave. Based on evolution of
hemispheric pattern...with strengthening cyclonic flow over
Hudson Bay and Gulf of Alaska...feel faster moving flow will
develop across the US and cut off this slow moving low...putting
Georgia in northwest flow aloft. Have therefore trended toward the European model (ecmwf) for
now...resulting in a drier forecast.
low pressure off the Carolina coast will continue to promote a
moist NE flow into the local area to affect all of the taf sites.
Question becomes how low will the individual sites go tonight with
both ceiling and visibility. That question has already been answered at pdk
and ryy where IFR conditions are already present. Expect other
sites to follow suit and have trended this forecast downward with
IFR to be predominant after midnight. Slow improvement through
Monday morning but have included an optimistic VFR transition
after 19z as mixing becomes more prominent.
//Atl confidence...00z update...
medium on IFR potential and duration.
High on remaining elements.
Preliminary point temps/pops...
Athens 60 71 57 73 / 40 30 10 10
Atlanta 63 72 60 75 / 40 30 10 10
Blairsville 57 73 55 73 / 30 20 10 10
Cartersville 60 76 58 77 / 30 20 10 10
Columbus 63 73 61 78 / 40 20 10 10
Gainesville 60 73 58 74 / 40 30 10 10
Macon 62 70 59 76 / 50 50 10 10
Rome 60 77 58 79 / 30 20 10 5
Peachtree City 62 72 58 76 / 40 20 10 10
Vidalia 62 69 60 75 / 80 60 20 5