Scientific Forecaster Discussion
fxus62 kffc 281948
Area forecast discussion
National Weather Service Peachtree City Georgia
348 PM EDT Wed Jun 28 2017
Short term /tonight through Thursday night/...
Moisture return has begun in earnest. Model precipitable water
values approaching 2" in the southwest by 12z, and are 2"+ across
the forecast area by 00z tomorrow evening. Weak mid/upper-level
wave is progged to be a little slower lifting out of the northern
Gulf into the region and I have slowed the spread of higher pops
into and across the forecast area accordingly. Still looking at
chance pops spreading up the western edge of the area by 12z but
likely pops lag until we approach afternoon. Mid-level lapse rates
are weak, as is the upper wave, so chances for severe thunderstorms
still look to be minimal, however chances for locally heavy rain
are looking pretty good.
Long term /Friday through Wednesday/...
Primary concern in the long term period is timing and likelihood
of mostly diurnally driven convection. Shortwave trough over MS/Alabama
on Friday progged to weaken and fill as it moves slowly east over
the southeast while front lifts north. By Saturday, what's left
of wave will be east of Georgia but not likely to see much subsidence
unless large mesoscale convective system moves over the state Fri afternoon or overnight.
12z models somewhat different on strength and timing with CMC
having more well defined wave and ec/GFS muddier/weaker. Wpc
favoring non CMC blend which agrees with local office consensus.
Translation from above paragraph means that convection will
become widespread on Friday afternoon and evening and may continue
overnight. Too soon to say whether severe storms are likely but
GFS/NAM are showing increasing low level moisture and instability
during the day (mlcape ~2000 j/kg) as front lifts north and east
as a warm front. Vertical wind shear quite weak with ~10kts 0-1k
bulk shear and 10-20kts 0-6km shear. Could see heavy rain if one
place could see more than 2 inches which could be possible based
on latest quantitative precipitation forecast.
After wave passes Sat, more broad wave moves east from lower MS
valley into eastern Continental U.S. Sunday. Lift not as well defined with
this system and appears associated front may never make much
progress into the state. Again, only CMC showing stronger wave and
more southward progress and as before, favoring non-CMC blend
with rest of long term forecast. Diurnal pops expected in this
pattern with 30-40 during the day and at most 20 during the night.
Attm, Holiday forecast for the 4th appears to show this
lower/climatological normal tstm chcs. Will continue to monitor,
but for now will take that as good news as recent 4th July events
have been very stormy.
Prev long term discussion follows.
Previous discussion... /issued 342 am EDT Wed Jun 28 2017/
Long term /Thursday night through Tuesday/...
Day to day forecast still consistent for the long term period. By
Thursday night the return flow has been established and we remain
under a south to southeast low level flow. Models still hint at a
short wave moving across central or south Georgia Thursday or Friday.
An upper trough deepening over the Great Lakes and into the Ohio
Valley over the weekend may help push a front into TN/KY.
So...likely pops look reasonable for north Georgia on Saturday and have
stayed with that. Into the first of the week the pattern is
unsettled and we remain in an unstable airmass. However there
looks like there may be some brief drying for the end of the
period but not enough to remove pops. Have lowered pops a bit for
Monday and Tuesday.
VFR conditions are expected to predominate through 06z. MVFR
ceilings and visibilities will develop across the far south and
southwest, spreading north and east into the kcsg, kmcn and Atlanta
Metro area taf sites by 12z. Local IFR conditions will be mixed into
this area as well at times. Kahn will likely see MVFR conditions by
14-16z. Scattered showers with isolated thunderstorms also spread
north and east into the forecast area beginning across the southwest
by 08z. Winds will be east to southeast 6-10kt through 00z,
diminishing to 6kt or less after.
//Atl confidence...18z update...
Medium concerning timing of lower ceilings and visibilities as well
as the onset of precipitation. High for wind speeds and direction.
Preliminary point temps/pops...
Athens 66 81 70 82 / 10 50 50 60
Atlanta 70 81 71 82 / 20 60 50 70
Blairsville 60 79 66 77 / 10 40 50 70
Cartersville 67 80 70 82 / 30 60 50 70
Columbus 73 83 73 86 / 30 70 50 60
Gainesville 68 80 68 79 / 10 50 50 70
Macon 70 84 71 86 / 20 60 50 60
Rome 68 81 70 83 / 30 60 50 70
Peachtree City 68 81 70 82 / 30 60 50 70
Vidalia 72 85 72 87 / 10 60 50 50