Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Peachtree City Georgia
813 PM EDT Friday Jul 3 2015
near-term grids updated to reflect observed trends and recent
guidance. Expect scattered convection in central Alabama to move east into
westcentral Georgia around 10pm then weaken after midnight.
A larger area of rain showers/thunderstorms and rain likely to move into northwest Georgia after
2am spreading slowly south and east. These storms should not be
severe but may produce periods of heavy rain...based on this will
keep Flash Flood Watch going. This weakening area of convection
Sat morning could affect local activities in the atl metropolitan
including the Peachtree Road race. Whats left of this precipitation
should continue to weaken with additional isolated/scattered convection in
the afternoon just about anywhere with preference for areas near
boundaries and gradients between thick cloud cover and sunshine.
Previous discussion... /issued 334 PM EDT Friday Jul 3 2015/
.Flash Flood Watch for north Georgia through Sunday morning...
Short term /tonight through Sunday night/...
moist and relatively fast (35-45kt) zonal low to middle level flow
continues to send one impulse after another across the southeast
region...supporting the multiple rounds of showers/thunderstorms
that will persist through at least Sunday.
Timing/duration/intensity of each "round" has been challenging given
rapid fluctuations with mesoscale environment. The area is in a bit
of lull this afternoon but expect things to pick back up late this
evening and overnight as next short wave approaches. Models actually in
pretty good agreement with this wave overnight...with the NAM being
the most aggressive showing a 1-3 inch maximum of 6-hour precipitation from
central Alabama to northeast Georgia between 06-12z/Sat. Track of short wave energy and
best low level convg seem to support the heavier rain occurring across
north Georgia late tonight/early Sat.
Any break in convection will be short-lived on Saturday as upper level
low strengthens over northern MS/western Tennessee around 00z/Sunday. Favorable
moisture/energy advection within pronounced southwest flow will
support additional showers/thunderstorms that will track across
Alabama/Georgia by Saturday evening into Sunday morning as upper low approaches
eastern Tennessee by 12z/Sunday. Additional heavy rain expected
Saturday night. Flood prone areas...especially across north Georgia...
will be susceptible to flooding/flash flooding through Sunday. Each
round of rain /tonight and again Saturday night/ could bring at
least an inch with isolated amounts up to 2 inches. Rough estimate of
the heaviest rain axis over the next 24-48 hours will be along and
north/west of a Carrollton to Marietta to Gainesville line...but
certainly this is not exact.
Given moist environment and limited heating due to clouds and
rain...severe potential will generally be low. However...similar to
today...if outflow-driven broken line/weak qlcs rolls into more
unstable airmass south and east of atl...expect a few strong to
marginally severe storms with damaging winds continuing to be
Long term /Monday through Friday/...
By Monday...upper level trough axis is over the eastern two thirds
of the area with some middle level drier air noted for the northern
County Warning Area with precipitable water dropping to 1.4 inches. Overall would
expect this to result in a reduction in coverage of storms over
previous days and plan only minor tweaks to currently advertised
middle to high end chance grids. Drier air continues for Tuesday
before eroding away and giving way to continued high moisture
atmosphere for the remainder of the long term. With middle and upper
level ridge building in however...upper level energy is much
reduced through the period and diurnally favored chance probability of precipitation look
suffice for the grids. Remainder of the forecast is on track and
no changes are planned.
primary concern is threat for thunderstorms and rain overnight and Sat afternoon.
Most likely scenario is that other than isolated thunderstorms and rain in westcentral
Georgia 02z-05z...area of rain showers/thunderstorms and rain likely over northwest Georgia after 05z
spreading into atl metropolitan around 07z. Not sure precipitation will make it
that far south...but most likely based on recent guidance. Precipitation
should clear about 2-4hrs after onset. No other big concerns. Surface
winds will remain on west component. MVFR ceilings/visibilities during
rain showers/thunderstorms and rain otherwise VFR.
//Atl confidence...00z update...
medium confidence on likelihood and timing of thunderstorms and rain.
High confidence on all other elements.
Preliminary point temps/pops...
Athens 69 84 68 86 / 40 40 30 50
Atlanta 71 82 69 83 / 50 50 50 60
Blairsville 64 74 63 78 / 70 70 50 60
Cartersville 69 79 67 82 / 70 70 60 60
Columbus 73 86 71 87 / 60 50 40 50
Gainesville 69 79 68 81 / 60 50 40 60
Macon 71 89 70 88 / 30 40 20 50
Rome 69 80 68 83 / 70 60 60 60
Peachtree City 70 84 69 84 / 50 50 40 60
Vidalia 73 92 72 92 / 40 30 20 40
Flash Flood Watch through Sunday morning for the following