Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
1258 am EST Wednesday Mar 4 2015
Previous discussion... /issued 718 PM EST Tuesday Mar 3 2015/
The Wedge of cool air over northeast Georgia remains in place this
evening. The warm front extends from near Dublin and Macon to
just south of Peachtree City. It should gradually move northeast
through the night with continued widespread fog and patchy rain
or drizzle north of the warm front. Most visibilities range from
1/2 to 2 miles which is above dense fog advisory criteria. Will
monitor closely if that changes. Have been adjusting hourly temperatures
and dewpoints to reflect current conditions. Expect temperatures north of
the warm front to remain steady or slowly rise during the night
with the frontal passage and a light southerly wind.
Short term /tonight through Thursday/...
just a hypothetical statement here...but its starting to seem like
winter will never end. Once again...dealing with winter weather
grids in the short term. The good news is that model guidance is
slowing down the front for Thursday just a tad...which means less of
a chance of wintry precipitation. More on that later.
In the meantime...hybrid damming remains firmly entrenched across
northeast Georgia with widespread clouds and light rain/drizzle
across the area. We were seeing some breaks in the clouds across
southern zones but they have since filled in with cumulus...and little
lifting expected. Trend should continue overnight and may have to
deal with some areas of dense fog in the morning. However...winds
shift around to southerly tomorrow which helps to scour out the
damming with the increasing low level warm air advection and should see some
sunshine on Wednesday. With that comes some really Spring-like temperatures
with highs in the 70s across most of the area...approaching 80
Some question still about convective potential on Wednesday and
isolated rumbles of thunder cannot be totally ruled out especially
across northwest and west central Georgia as the front begins to
approach...but thinking for now chances are just too low to include.
This will be reevaluated later tonight.
As mentioned above...guidance continues to slow down the front...
with frontal precipitation really pushing into northwest Georgia
after 06z Thursday. Temperatures really plummet after 06z across
extreme northwest zones with most definitely a non-diurnal trend in
temperatures on Thursday...but a substantial /+10c/ warm nose remains as
the upper front lags behind the surface front. Low-level cold layer
drops below freezing for kcha as early as 10z Thursday but surface
temperatures still above freezing...which of course would not be supportive
of freezing rain so it looks like at onset whatever mix there might
be would be more likely some light sleet mixing in with the rain.
Once temperatures drop below freezing...maybe closer to 15z or so...
could see more of a freezing rain/sleet mix. Overall accumulations
will be very light as by the time the temperatures drop enough to
matter the best quantitative precipitation forecast will be pushing southeast. But with that... have
added a very small amount to the snow grids to account for minor
accumulations of sleet possible /less than a quarter inch/ and with
the continued chance of a Glace...less than a tenth of an inch...of
As with any winter event across Georgia...this is all dependent on
timing of incoming colder air vs. Exiting moisture...but that said
current guidance and guidance trends all point to that this is not
going to be much of a wintry event. However...with temperatures
dropping during the day on Thursday...any wintry precipitation may result
in black ice especially on bridges and overpasses. Will issue a Special Weather Statement
for portions of extreme north Georgia.
Long term /Thursday night through Tuesday/...
mainly only tweaks to the long term based on the latest guidance.
Lots of uncertainty for precipitation potential between the GFS and
looks cool but generally dry for Thursday night/Friday but
temperatures rebound nicely into the weekend as generally zonal
upper-level flow pattern keeps the better cold air north and west of
the forecast area. Hard to go above slight chance/low chance for
probability of precipitation through any of the remainder of the extended forecast period as
no significant focus for better...more organized...precipitation
chances are evident in the persistent zonal flow.
wedge of low clouds and fog is finally beginning to erode on the
southwest side. Meanwhile...the northern terminal sites remain
locked in at 1/2sm to 1/4sm fog and vlfr ceilings. The tricky part of
the forecast will be to time the edge of the clearing. Do think
when the fog and low clouds clear...it will go very very quick. My
timing of improving visibilities and ceilings at atl will likely have to be
adjusted depending upon the speed of clearing on the SW side. East
winds will switch around to the S and then SW quickly also...went
with the rap because it held onto The Wedge a few more hours than
the other models which are notorious for clearing too soon. Cold
front will begin to drop south today...bringing an area of precipitation.
Didn't adjust probability of precipitation for this cycle as models are in pretty good
agreement with timing. However...a few tweaks may have to be made
for later taf issuances.
//Atl confidence...06z update...
medium confidence all elements.
Preliminary point temps/pops...
Athens 73 58 59 31 / 10 60 70 10
Atlanta 72 50 53 29 / 20 70 70 5
Blairsville 65 44 47 24 / 50 80 70 5
Cartersville 71 41 44 26 / 40 80 70 5
Columbus 75 59 61 34 / 10 60 60 20
Gainesville 69 51 53 29 / 30 80 70 5
Macon 77 62 63 36 / 5 40 60 30
Rome 71 38 41 25 / 50 90 70 5
Peachtree City 73 54 56 30 / 20 70 70 5
Vidalia 81 63 73 41 / 5 10 50 30
dense fog advisory until 10 am EST this morning for the
following zones: Baldwin...banks...Barrow...Bartow...Bibb...