Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Peachtree City Georgia
134 am EDT Thursday Aug 28 2014
/issued 1047 PM EDT Wednesday Aug 27 2014/
quiet weather expected to continue tonight. Forecast low
temperatures running 2-7 degrees below normal.
Short term /tonight through Thursday night/...
/issued 251 PM EDT Wednesday Aug 27 2014/
still looking at a generally dry short term forecast period with
mild to cool nights and warm days. Surface ridge has broken down
but moisture return has not yet begun and remains fairly
unimpressive until late in the period. With the upper ridge also
weakening and marginal moisture/instability expected along the
northern fringes of the forecast area I have kept the slight
chance probability of precipitation for possible isolated late afternoon/early evening
convection in the northeast mountains where terrain may provide
just enough extra push for a few showers/thunderstorms Thursday.
Thicknesses continue slowly rising allowing for daytime highs at
or above seasonal normals...however one more dry and calm night
will allow good radiational cooling tonight for below normal lows.
Lows creep up toward seasonal normals for Friday morning...but
should remain comfortable due to lower than normal dew points.
Long term /Friday through Wednesday/...
/issued 251 PM EDT Wednesday Aug 27 2014/
Friday continues the dry trend with weak ridging still in place
aloft...but changes coming for the weekend as a shortwave digs and
deepens across the plains. As the wave train pushes east...
widespread moisture spreads across the southeast for the weekend
in the southwest flow aloft. Ridging still holds on strong in the
western Atlantic so there continues to be at least some
uncertainty as far as how significant the rain might be. The 12z
European model (ecmwf) has trended a little wetter than the 00z run which had kept
most...but not all...of the significant precipitation just to our
north and west. The 12z GFS really brings the rain into our
area...partially due to the upper high centered a little farther
east and a tad weaker...but also because of a stronger Lee low
developing east of the Appalachians. Add the typical summertime
diurnal trend on top of it and of course the afternoon and early
evening hours are prognosticated to see the most convection. As might be
expected...it is impossible to tell at this point if any one area
will see more or less rain /with summertime convection it is
usually impossible to tell this even the day of much less three
days out/ but confidence is increasing in the transition to the
wetter pattern especially with the 12z European model (ecmwf) coming more into
agreement with the GFS. Not expecting really anything severe aside
from an isolated pulse storm or two and not expecting any
hydrology impacts...but enough to ruin outdoor plans over the
weekend. We will be monitoring. See previous discussion below.
Long term /Thursday night through Tuesday/...
/issued 312 am EDT Wednesday Aug 27 2014/
looks to be a transition day as we begin the extended period as
upper high begins to shift offshore the Carolinas coast and
moisture begins to stream in off the Gulf of Mexico. Models have
been slowing the evolution of these two features with each run
with the European model (ecmwf) slower than the GFS at this point. Still expect a
modest increase in shower and thunderstorm potential for southern
sections given precipitable water values approaching 1.5 inches
late in the day. Will therefore carry low end chance probability of precipitation for the
southern tier and also for the mountains where the southerly flow
should allow for some slope induced lift and subsequent thunderstorm
Likewise...for the weekend...models have slowed progression of
upper trough and also have some significant differences on the
evolution of the trough itself. European model (ecmwf) is decidedly slower with
moisture return and further north with main energy impulse
resulting in highest probability of precipitation over western portions. GFS on the other
hand pumps copious amounts of moisture into the area with
precipitable water values approaching 2.25 inches and upper trough
moving directly across the area Sunday. For now in the
grids...have played it as a slow start to the precipitation on Saturday
with a sharp gradient from west to east. For Sunday however...feel
even with a glancing blow of upper support as European model (ecmwf)
suggests...enough moisture is present to warrant high probability of precipitation.
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 94 68 / 5 5 5 5
Atlanta 91 69 93 71 / 5 5 5 10
Blairsville 88 62 88 62 / 10 10 10 10
Cartersville 92 64 94 67 / 5 5 5 10
Columbus 93 68 95 72 / 5 5 10 10
Gainesville 91 68 92 68 / 5 5 5 10
Macon 94 65 95 70 / 5 5 10 10
Rome 92 64 94 67 / 5 5 5 10
Peachtree City 92 64 92 67 / 5 5 5 10
Vidalia 94 68 95 73 / 5 5 10 5