Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
341 am EDT Thursday Aug 28 2014
Short term /today through Friday/...
Although the upper ridge has been weakening...its still in place
across the southeast and will linger through the short term.
Originally thought that the moisture across the Ohio Valley
yesterday would sink southward enough today to allow for isolated
thunderstorms across the mountains today...however latest guidance
suggests this moisture will remain north of the County Warning Area. Guidance has
backed off on precipitation across the NE Georgia mountains and hi res models
are not picking up on development this afternoon across this area.
Thus...have taken out the slight chance /20 percent/ probability of precipitation across the
northeast...but still mention 10 percent chance in the grids.
For Friday...start to see the evidence of moisture return off the
Gulf along the Gulf Coast but doesnt quite make it into the southern
portions of the County Warning Area. Have continued with a dry forecast for Friday.
Thickness values continue to increase for today so expect high
temperatures to be one to three degrees warmer than yesterday with
most areas making it into the 90s...the exception being the
mountains. High temperatures continue to remain above normal while
low temperatures continue to remain below normal.
Long term /Friday night through Wednesday/...
Extended period still contains quite a bit of uncertainty but at
least some marginal improvements to model consistency noted this
run. We begin the extended in a transition period as surface high
over the Ohio Valley shifts east off the Atlantic coast in
response to upper level trough kicking out of the Midwest states
and into the Ohio Valley. This will be a key component in our
local weather as low level winds shift to a southerly direction and
pumps moisture northward out of the Gulf of Mexico. This will
bring precipitable water values back above 2 inches for most of
the area on Saturday and this combined with modest shortwave
energy over the northwest zones should lead to likely coverage of
storms along and west of the Interstate 75 corridor. Westerly
steering flow may bring these storms further east than what is
currently depicted in grids and will need to monitor with
subsequent model runs for a possible adjustment upward.
After a few days of suggesting Sunday as the wettest day of the
weekend...models now agree on slightly less coverage. First wave
of shortwave energy lifts north of the area leaving local area
without large scale lift for Sunday. In addition...in the wake of
the shortwave...some drier middle level air works in which the European model (ecmwf)
really picks up on. Still feel far northwest zones will see better than
average rain chances given moisture in place and will go with
likely but transition with a sharp gradient to just low to Middle
Range chance for the remainder of the forecast area.
Middle and upper level ridge build back over the area through next
week but features are not particularly strong. Likewise...deep
layer moisture not anything to write home about and all this
points to climatology probability of precipitation for the remainder of the extended.
winds will be light throughout the taf period and because of this
the direction may be somewhat variable at times. Overall
though...the winds should be generally on the west side at atl and
become more SW by tonight. Expect cumulus field to form again
today...but only few in terms of coverage.
//Atl confidence...06z update...
high confidence on ceilings and visibilities. Medium confidence on wind.
Preliminary point temps/pops...
Athens 93 65 95 67 / 5 5 5 5
Atlanta 90 69 92 71 / 5 5 5 10
Blairsville 87 62 87 61 / 10 10 10 10
Cartersville 92 62 93 66 / 5 5 5 10
Columbus 94 68 94 73 / 5 5 10 10
Gainesville 90 68 91 68 / 5 5 5 10
Macon 93 62 95 68 / 5 5 10 5
Rome 92 62 93 66 / 5 5 5 10
Peachtree City 91 61 92 67 / 5 5 5 10
Vidalia 94 67 94 72 / 5 5 10 5