Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
332 PM EDT Sat Mar 15 2014
Short term /tonight through Sunday night/...
forecast area remains under increasing southwesterly upper flow
through the period as the upper trough axis remains west of the
state. Wedge front backs into the region tonight and holds its
ground through Sunday evening against the approaching surface low
associated with the upper system. Precipitation spreads over north
and central Georgia tonight into early Sunday. Instability increases
early Sunday and thunder is possible across most of the area by
midday. I have included a slight chance for thunder a little further
north and east over The Wedge as some elevated convection should
make it onto the cool side of the front. Chances for severe
thunderstorms are limited as the best instability and low/mid-level
shear remain a bit out of sync and much of the northern and eastern
portions are dominated in the lowest levels by The Wedge...but
cannot be dismissed entirely as ample deeper layer shear remains
present through much of the day due to stronger upper-level winds.
Better precipitation begins pushing east of the area overnight
Sunday into early Monday...but with the upper trough axis still west
of the state probability of precipitation remain relatively high.
Quantitative precipitation forecast totals through Monday come out around an inch and a half...and
although isolated minor flooding is a possibility...no widespread
hydrological issues are expected at this time.
Long term /Monday through Saturday/...
guidance agrees with shortwave energy and overrunning moisture
still advecting northeastward on Monday into Tuesday. Discrepancies exist
in the strength of the cad wedge and the progression of the
trough/moisture. 12z NAM is cooler/stronger wedge but warmer blend
of guidance looks most reasonable with Monday night lows in upper
30s to low 40s. Have overall trended temperatures down a bit from
previous forecast per latest blend through Tuesday. Have also
adjusted probability of precipitation along with prognosticated slug of isentropic upglide
lingering into Tuesday for portions of the east. This less
progressive solution is carried by the NAM and 12z European model (ecmwf) and seems
more likely than the quicker GFS. Otherwise have left rest of
forecast period alone with minor adjustments due to uncertainty
with guidance variation. Previous discussion follows...
Previous discussion... /issued 357 am EDT Sat Mar 15 2014/
Long term /Monday through Friday/...
European model (ecmwf) and GFS are in fairly good agreement with both showing an
upper disturbance pushing a weak surface low across parts of
central and south Georgia Monday and Monday night. The driving
upper disturbance does not push east of the area until Tuesday...
so wrap around moisture and patches of light rain may linger on
Tuesday. As the surface low approaches on Monday... models show a
cool wedge of high pressure nosing down from the northeast and
providing a stable air mass over the area Monday and Monday night.
This suggest the greater thunderstorm threat will be across south
Georgia and Florida Monday-Tuesday as the low pressure system
moves across. However... if the warm front is able to advance into
parts of central Georgia Monday afternoon... isolated
thunderstorms may have to be added with later forecast.
Otherwise... long range models show a weak cold front possibly
bringing a low chance of rain to the area by middle week... with the
GFS the fastest and showing a frontal passage on Wednesday... while the
European model (ecmwf) shows Wednesday night-Thursday. Both are fairly dry with
this system... so will only show a slight chance of showers across
north Georgia Wednesday and Wednesday night for now. Models show dry
high pressure settling over the deep south for Thursday and
VFR conditions are expected to predominate through 06z with some
lower /040-060/ VFR ceilings developing by around 00z. MVFR
conditions spread from west to east across the area 06z-10z with IFR
conditions developing 12z-18z. Precipitation spreads across the area
from west-east as well beginning as early as 00-06z in the west...
with widespread rain and...embedded...isolated to scattered
thunderstorms after 12z. West winds 5-10kt will back to
southwesterly and eventually southeasterly through 00z...eventually
becoming easterly across the forecast area by 18z. Wind speeds will
diminish some after 22z becoming 3-6kt through 12z before increasing
to 7-12kt by 18z.
//Atl confidence...18z update...
medium on timing for ceilings and onset/progression of precipitation.
High on all other elements.
Preliminary point temps/pops...
Athens 50 56 45 48 / 90 100 80 70
Atlanta 52 60 47 51 / 90 100 70 60
Blairsville 47 52 44 49 / 90 100 70 50
Cartersville 51 60 48 53 / 100 100 60 60
Columbus 54 66 56 63 / 80 90 70 70
Gainesville 50 54 43 46 / 90 100 70 60
Macon 52 66 54 58 / 70 90 80 70
Rome 51 61 49 54 / 100 100 60 50
Peachtree City 50 63 49 53 / 90 100 70 70
Vidalia 56 72 58 59 / 50 80 80 90