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Area forecast discussion 
National Weather Service Peachtree City Georgia
256 am EDT Friday Apr 18 2014

Previous discussion... /issued 730 PM EDT Thursday Apr 17 2014/

Short term /tonight through Friday night/...
main concern is with quantitative precipitation forecast as an area of low pressure allows for
overrunning Gulf moisture against a strong classical cad wedge from
a parent 1040+mb surface high sliding off the New England coast. Models
are at least in good agreement with the upper levels closing off a
low and enhancing the forcing for widespread precipitation mainly Friday
afternoon into Friday night. There are some decent discrepancies
with the track of the surface low and amount of moisture. The last 2
runs of the GFS have been farther north and quite robust on
quantitative precipitation forecast...while the NAM has been farther south and drier...with the
European model (ecmwf) a bit of a compromise between. See hydrology section below for
more on quantitative precipitation forecast and increasing flood threat.

For probability of precipitation and weather...have trended onset of likely probability of precipitation in the
southwest County Warning Area sooner than guidance as isentropic upglide typically
allows for precipitation before the model solutions. Have ramped up after
06z tonight and spread into definite probability of precipitation across central during
daytime Friday with likely to chance into north Georgia. Wedge should
keep environment stable so left out thunder mention. Overall
confidence in evolution of this system is near medium as some models
are indicating a dry slot nosing into southern portions of the area
for Friday night and overall coverage of showers may be increased in
parts of north Georgia with any banding that occurs in the deformation
zone of the low as it pushes south and east of the County Warning Area. Have trended
likely and chance probability of precipitation to eastern portions late Friday night with
wrap-around moisture keeping some chance probability of precipitation lingering into the
start of the long term.

For temperatures...tricky forecast for Friday with influence of wedge and
moisture overrun. Have leaned away from MOS and trended cooler
though not as extreme as raw GFS. Looking at many areas staying in
the middle to upper 50s for highs...and near record low maximum values for
Columbus and Macon /possibly Athens/.


HPC guidance looks like a reasonable compromise from the vast
spectrum of other model quantitative precipitation forecast solutions. This brings 2 to 2.5 inches
prognosticated in a 24-hour period across much of central Georgia and is closer to
the European model (ecmwf) and sref...while the GFS is robust with up to 4 inches in
the SW...and the NAM is anomalously dry. Have gone with a Flood
Watch based on these raised updated amounts generally along and
south of a Hamilton to Forsyth to Warrenton line. One could argue
the better threat is a bit farther south where recent rainfall has
brought amounts to 100-200 percent of normal and above normal 7 day
stream flows...though uncertainty with possible higher amounts
farther north weighed into the current watch extent. This will be in
affect from 12z Friday to 12z Saturday.


Long term /Saturday through Thursday/...
closed upper low discussed above will be slow to move out of
region Sat and even early sun. Good model agreement on 500 mb/surface
height and wind fields though less agreement with quantitative precipitation forecast. Upper low
forecast over south central Georgia 12z Sat with 12z GFS slightly north of
median of model solutions and 12z European model (ecmwf) furthest south. By 12z sun
upper low prognosticated only to move 500nm off Georgia coast. Clouds will
linger late Sat and even through early sun in eastern counties. Could
also see some lingering light rain through Sat as well. With the
clouds and low thickness values...temperatures will remain below average
Saturday with a quick rebound next week.

Next system still looking interesting with weak shortwave in west-northwesterly
flow aloft prognosticated to affect area on Tuesday. Unusual to see this
kind of pattern in late April. With more moisture and stronger
lift...might see a line of storms or mesoscale convective system. Temperatures will be a little
above normal and with dewpoints in the 50s and low 60s...MLCAPE
values will be sufficient for some strong storms. Deep shear will
be somewhat weak...0-6km bulk shear only 10 to 15 kts. Will
continue to monitor.



Records for Friday April 18...

Maximum temperature min temperature
station high low high low
------- ---------- ---------- ---------- ----------
kahn 90 1942 54 1902 64 1969 32 1936
katl 87 2002 50 1983 69 1927 33 1997
kcsg 91 2002 62 1983 69 2006 37 1962
kmcn 90 1967 55 1921 66 1922 33 2001

Records for Saturday April 19...

Maximum temperature min temperature
station high low high low
------- ---------- ---------- ---------- ----------
kahn 91 1917 51 1984 64 1927 30 1983
katl 88 1941 50 1983 66 1927 30 1983
kcsg 91 2002 59 1983 68 1995 33 1983
kmcn 91 2002 59 1910 66 1927 31 1983


06z update...
rain showers continues to work its way northward from the Gulf Coast and
will impact csg terminal first followed by mcn and then the
atl area terminals. Ceilings following suit thus far with mainly VFR
over the local area but MVFR quickly developing within rain
shield just south of the area. Expect a quick transition to MVFR
for all terminals later this morning and then IFR by late this
afternoon. Advertising a later clearing trend than models indicate
and keep IFR throughout entire taf cycle. As far as
this afternoon and especially this evening into the
overnight...could see some high gusts to as high as 30 kts.
Withing heavier rain showers...these values could be even a little higher
and will be monitored closely.

//Atl confidence...06z update...
medium on IFR timing and wind gust potential.
High on remaining elements.



Preliminary point temps/pops...
Athens 56 46 62 46 / 60 70 30 5
Atlanta 55 47 62 49 / 60 60 20 5
Blairsville 55 44 65 45 / 40 60 20 5
Cartersville 58 48 66 46 / 50 50 20 5
Columbus 56 49 65 50 / 100 70 30 5
Gainesville 54 47 61 47 / 60 60 30 5
Macon 55 48 63 46 / 100 80 40 10
Rome 60 47 68 47 / 40 40 10 5
Peachtree City 55 46 63 45 / 70 60 30 5
Vidalia 59 53 67 52 / 90 80 40 20


Ffc watches/warnings/advisories...
Flood Watch from 8 am EDT this morning through Saturday morning
for the following zones: Baldwin...Bibb...Bleckley...



Short term...deese
long term....01