Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
228 PM EST sun Dec 28 2014
Short term /tonight through Tuesday/...
short term still dominated by southwest flow aloft as shortwave
over the Southern Plains and lower Mississippi Valley moves east
and continues to damp. Gulf moisture still being pumped into the
southeast with anomalously high precipitable water values...12z kffc sounding was
1.6 inches which is above the 99th percentile and not far from the
record values. Second wave of precipitation should push into north
Georgia tonight as the shortwave continues to damp and push east
into the southeast. Attendant surface front will push most of the
rain out of the area by Monday afternoon...but the front will
elongate and stall allowing some lingering precipitation across extreme
southeast zones Monday night into Tuesday. Additionally...wrap
around moisture on the back edge will allow for some lingering
light rain showers across extreme northeast Georgia.
Still pretty much zero MUCAPE to deal with and while we cannot
completely rule out an isolated rumble of thunder here and there
especially in the heavier rain...not enough of a concern to add
thunder at this time. Forecast quantitative precipitation forecast through the short term is
pretty small...with generally less than half an inch additional
rain expected. This is despite the high precipitable water values and very
efficient rainfall processes. Might be hard-pressed to get any
flooding as this system wraps up but will leave the Flood Watch in
Temperatures will continue above-average especially for overnight
lows and for highs in southern zones ahead of the front. Went with
a general blend through the period. We will start noticing the
effects of the cold front more drastically in the extended.
Long term /Tuesday night through Sunday/...
next system for late Thursday night into Friday morning is
shaping up to be an interesting one from the outset. We had been
advertising temperatures right around freezing for some of the valleys as
the precipitation moves in and now the new guidance comes in even lower
with some temperatures around freezing even along our western tier of
counties. Taking a look at the model Cobb output however for
Brasstown Bald...it is evident that the low temperatures will be around
03z...just ahead of the precipitation shield and rise through the night
into the middle 30s by 12z. There still could be some cold air locked
into the valleys so would like middle shift to get a look at another
run before pulling frozen precipitation on this cycle.
Severe potential has not really changed from this time yesterday
as cape builds to a high of around 1000 j/kg over the southern
tier Sunday afternoon with best shear remaining to the north. Do
have 30 to 35 kts at 850mb across the southern tier and there is
actually an earlier lower jet around 925mb that pushes a 40 knots maximum
across the Atlanta metropolitan so will continue slightly enhanced
wording in the severe weather potential statement.
Timing issues remain with the 12z GFS maintaining a slower
solution in clearing things out. Have yet to see the European model (ecmwf) for the
12z run but will likely just keep the low end chance probability of precipitation in there
as a hedge for the extended until more agreement is reached. Based
on the last week...am leaning toward a less progressive front and
a wetter pattern to continue.
widespread IFR at taf time with the exception of mcn. See little
improvement during the afternoon. May see brief lifting with onset
of second round of -ra this evening/overnight but overall IFR
expected everywhere...and cannot rule out brief IFR ceilings. May see
some improving to MVFR toward the end of the period at atl. Expect
MVFR to IFR visibility as well...and cannot rule out brief fog. SW winds
to start the period will continue to veer to northwest toward the end...
generally under 5kt.
//Atl confidence...18z update...
high on winds.
Medium-high on all other elements.
Preliminary point temps/pops...
Athens 51 59 45 58 / 90 60 20 10
Atlanta 51 60 46 57 / 100 40 10 5
Blairsville 46 56 42 49 / 100 50 30 20
Cartersville 46 56 42 51 / 100 40 10 5
Columbus 55 63 48 62 / 80 60 20 5
Gainesville 49 57 45 54 / 100 40 20 10
Macon 56 64 47 63 / 80 80 30 5
Rome 46 55 41 51 / 100 30 10 5
Peachtree City 51 61 43 59 / 90 40 10 5
Vidalia 60 67 53 64 / 40 70 60 10
Flood Watch through Monday morning for the following zones: