Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
631 am EST Thursday Dec 12 2013
Previous discussion... /issued 232 am EST Thursday Dec 12 2013/
Short term /today through Friday/...
a dry cold front is situated across north central Georgia this morning.
No precipitation associated with the boundary...but there is definitely a
dewpoint gradient and some high clouds. North of the front dewpoints
are in the middle 20s while south of the front...dewpoints are in
the upper 30s to lower 40s.
Cold front will continue southward today with high pressure building
across the state this afternoon/eve. The high pressure will remain
the dominate weather feature throughout the remainder of the short
term period...but will begin to shift to the east on Friday.
With the high center shifting to the east...winds will switch around
to the east/southeast allowing for the low level moisture to increase. With
the increasing moisture...clouds will also increase with skies
becoming partly cloudy to mostly cloudy.
Took blend for temperatures with close to zero probability of precipitation through the period.
Only adjustment to guidance was to decrease dewpoints in the northwest
flow a few degrees.
Long term /Friday night through Wednesday/...
extended begins with weak southwest flow aloft and sharp shortwave
and attendant surface low and front across the Southern Plains
bringing moisture up into the mid-south. Rain pushes into
northwest Georgia generally after midnight Friday night...
overspreading the state on Saturday. Meanwhile...diabatically
enhanced classical cad onset is expected around the same time as
precipitation enters...and with temperatures in northeast Georgia dropping into
the lower to middle 30s...cannot rule out some brief flurries mixed
in before 12z. Expect widespread rain during the day on
Saturday...and with another shortwave ejecting from the Desert
Southwest on Saturday...should bring a reinforcing wave of precipitation
to mainly central Georgia overnight Saturday night into early
Sunday. European model (ecmwf) is a little more bullish with this second round.
Front exits the area Sunday afternoon and evening...with cool and
windy conditions expected behind it. Though mean trough remains in
place generally through the remainder of the extended...mainly
clear conditions dominate and we should see some moderation
/slight warming/ in the temperatures. Another shortwave prognosticated to move
through the northwest flow aloft late Tuesday but for now have
only increased cloud cover a tad on Wednesday. Both models show a
more significant system beyond the end of the period...but it is
Worth mentioning even this early given unusual agreement between
GFS and European model (ecmwf)...so it bears watching.
Quantitative precipitation forecast amounts range generally between 1-1.5 inches through the event
so as with the previous event...not really expecting enough in a
short enough period of time to warrant much in the way of flash
flooding...but isolated to scattered minor river flooding not out
of the question. MUCAPES Saturday afternoon creep up to between
200-300 j/kg...pretty much all elevated. Have kept mention of
isolated thunder south for Saturday afternoon but confidence is
relative humidity values will dip to between 20 and 25 percent this
afternoon...with winds gusting to around 20 knots. However...fuel
moisture values remain mostly above 9 percent.
Had to adjust the dewpoint forecast down from model guidance. Do
think the downsloping northwest flow will allow more drying.
high pressure will continue across the region through the period.
Winds may gust to around 20kt today in northwest flow. Little...if
any...cloudiness expected until tomorrow. Even then...only cirrus.
So...no ceiling/visibility restrictions anticipated. As the high center
shifts to the east tomorrow...winds will shift east/southeast during the
//Atl confidence...06z update...
high confidence all elements.
Preliminary point temps/pops...
Athens 49 30 52 40 / 0 0 5 50
Atlanta 45 30 52 44 / 0 0 5 60
Blairsville 40 24 49 35 / 0 0 10 70
Cartersville 42 26 51 40 / 0 0 10 70
Columbus 51 31 55 47 / 0 0 5 60
Gainesville 46 29 50 41 / 0 0 10 60
Macon 52 29 55 44 / 0 0 5 30
Rome 42 26 51 38 / 0 0 10 70
Peachtree City 46 26 52 40 / 0 0 5 60
Vidalia 54 32 57 47 / 0 0 5 10