Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
339 PM EDT Thursday Mar 26 2015
Short term /tonight through Friday night/...
convection in the Gulf has helped to suppress activity across the
County Warning Area and only a few light showers have been noted across the area
today. Rain to the south is slowly moving northward...however it
appears the bulk of the precipitation at this point will be
overnight and more associated with the cold front. Instability is
decent enough with mu cape around 500 j/kg in the GFS and 1000 j/kg
in the NAM that I have continued the slight chance of thunderstorms
overnight /with higher rain chances/. Not expecting severe storms
overnight...however still could see some gusty winds or small hail
with the isolated thunderstorms.
Cold front will move into south Georgia tomorrow and may see some
showers across the southeast part of the County Warning Area in the morning...but
thunderstorms should have diminished by then. Will see winds
increase late tonight/tomorrow behind the front with sustained
values around 15mph /but below Wind Advisory criteria of 20mph/.
Will need to watch trends for Friday afternoon into the evening
closely. Models are hinting at light precipitation across the far
north...but for now have only mentioned 10 percent probability of precipitation in grids.
Will definitely see an affect on temperatures with this cold front.
For Friday...high temperatures will be about 10-20 degrees cooler
than this afternoon. For Saturday morning...expect some freezing
temperatures in the north. Based on this...have gone ahead and
issued a freeze watch for portions of northwest Georgia. Even though the NE
counties are expected to be below freezing Saturday morning...the
frost/freeze program does not start for those counties until April
Long term /Saturday through Thursday/...
extended models are coming into better agreement at the start of the
extended period. 12z NAM/GFS showing moisture diving on the backside
of the trough further to the west...and not reaching West Georgia until
Saturday evening...more in line with the sref/ECMWF...have kept
slight chance probability of precipitation in 00-06z Sunday but expect mainly an increase in
cloudiness Saturday afternoon.
Models keep northwest flow aloft and continue to show coldest
temperatures Sunday morning....and will need to continue monitoring
for possible frost/freeze. Made minor changes to temperatures with
freezing line a little further south. Still not cold enough to
break records per attached records below.
GFS/European model (ecmwf) still showing discrepancies in handling of front on
Monday and system through the end of the week. Have only tweaked
temperatures through this time frame with previous thinking
/Issued 359 am EDT Thursday Mar 26 2015/ temperature bust potential alert
for Saturday afternoon... particularly across the western portion of
the County Warning Area. GFS and NAM start the period with deep trough entrenched
across the region and backside shortwave diving southeast and deep
moisture moving through the middle MS valley. Both GFS and NAM
guidance suggesting low end rain chances with this feature late Sat
am into the afternoon. Given the very cold thermal profile across
the area...any saturation of the column would keep temperatures a good 10
degrees below current forecast as a result of any precipitation falling
through the layer. Its a good thing we are in late March after
looking at the GFS soundings for Saturday. Have put low probability of precipitation in to
account with light rain mention...but not all models as bullish with
the deep moisture and backside shortwave Aka sref and European model (ecmwf). For
now..will keep low pop mention and hold temperatures in the 50's areawide.
As an for your information...record low maximum temperature at csg on Saturday is 48.
Coldest morning still appears to be Sunday morning with best
radiational cooling areawide. General freezing line running from
Newnan to Peachtree City to Athens and points north. Will certainly
have to consider frost/freeze concerns given clear skies...light
winds...and higher relative humidity values...even in areas across the south...as
frost can occur in air temperatures above freezing. Still not forecasting
record temperatures but will certainly be within a few degrees of the
records at all sites.
GFS and European model (ecmwf) in better agreement today over another front moving
through the area on Monday. Have put rain chances in the forecast
starting Monday am...albeit low chances with no mention of thunder.
Models diverge a bit on Tuesday despite having the same general
northwest flow pattern across the region. GFS more bullish with
bringing a strong shortwave eastward out of Texas and thus much more
available moisture for general showers/low end probability of precipitation across the area.
European model (ecmwf) has almost no accounting of this feature thus pitting the
forecast between a generally dry one vs a wet forecast Tuesday
through Thursday of next week. For now...have chance probability of precipitation in each
day and favor the GFS as it has been fairly consistent with this
feature for several days now. Shortwave...per GFS...approaches late
Wednesday into Thursday and thus probability of precipitation will increase a bit more. Keeping
thunder out for now...but will have to see how this feature evolves.
Records for 03-29
Maximum temperature min temperature
station high low high low
------- ---------- ---------- ---------- ----------
kahn 85 1928 47 1959 62 1977 25 1887
katl 84 1989 43 1894 65 1924 25 1887
kcsg 89 2007 52 2001 67 1997 32 1955
kmcn 87 1907 47 1926 67 1924 30 1966
Previous discussion... /issued 149 PM EDT Thursday Mar 26 2015/
for the most part...have pushed back the timing of the showers in
the tafs. End time of showers in the tafs may be a bit on the long
side. There is a slight chance of a thunderstorm tonight at the
taf sites...but too low to mention in the tafs. This will need to
be watched closely though. Winds should remain the west side but
transition from SW to northwest overnight with increasing wind speeds for
//Atl confidence...18z update...
high confidence on wind. Medium confidence on ceilings...visibilities and
timing of precipitation.
Preliminary point temps/pops...
Athens 54 62 34 53 / 80 20 5 0
Atlanta 50 58 34 51 / 80 10 5 5
Blairsville 44 51 27 44 / 70 10 10 5
Cartersville 46 57 32 50 / 80 10 5 5
Columbus 52 63 38 57 / 70 10 0 10
Gainesville 49 58 32 50 / 80 10 0 0
Macon 56 64 37 56 / 60 30 0 5
Rome 46 56 31 50 / 70 10 5 5
Peachtree City 50 60 33 53 / 80 10 5 10
Vidalia 62 68 40 58 / 60 60 5 0
freeze watch from late Friday night through Saturday morning for
the following zones: Bartow...Catoosa...Chattooga...Dade...