Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
208 am EDT Friday Mar 27 2015
Previous discussion... /issued 830 PM EDT Thursday Mar 26 2015/
latest surface analysis shows the cold front now pushing into far northwest
Georgia... and timing tool indicates the front will push across the
Atlanta metropolitan area between midnight and 2 am Friday morning. Expect
the rain showers to the west and SW in Alabama to push into west
central Georgia in the next hour...then into the Atlanta metropolitan area by 10
PM this evening if not earlier. Still cannot rule out an isolated
thunderstorm just ahead or along the front...with the greater
chances of this over central Georgia overnight. Have updated zones to
tweak lows down a degree or so based on temperatures seen upstream behind
the front... and to adjust probability of precipitation and timing of mention of thunder.
Otherwise... rest of forecast looks on track with showers likely all
zones and gusty northwest winds moving in behind the front overnight. /39
Short term /tonight through Friday night/...
/issued at 339 PM EDT Thursday Mar 26 2015/
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/...
/issued at 339 PM EDT Thursday Mar 26 2015/
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
Previous long term.../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
cold front has made its way into the northern most taf sites bu
-shra continue even behind this frontal boundary. A mixed bag thus
far of IFR...MVFR and VFR ceilings associated with this feature and
will handle with short term tempo to account for the potential
ovc008 through 10z. Thereafter...should see MVFR ceilings transition
to VFR by middle morning as winds increase from the northwest to 15g25kt.
//Atl confidence...06z update...
high on all elements.
Preliminary point temps/pops...
Athens 62 34 53 31 / 20 5 0 5
Atlanta 58 34 51 32 / 10 5 5 10
Blairsville 51 27 44 26 / 10 10 5 5
Cartersville 57 32 50 29 / 10 5 5 10
Columbus 63 38 57 35 / 10 0 10 20
Gainesville 58 32 50 31 / 10 0 0 5
Macon 64 37 56 33 / 30 0 5 10
Rome 56 31 50 28 / 10 5 5 10
Peachtree City 60 33 53 30 / 10 5 10 20
Vidalia 68 40 58 35 / 50 5 0 5
freeze watch from late tonight through Saturday morning for the
following zones: Bartow...Catoosa...Chattooga...Dade...Floyd...