Area forecast discussion
National Weather Service Peachtree City Georgia
1052 PM EDT Tuesday may 21 2013
Update...
updated to include some probability of precipitation through midnight for west central Georgia as
westward moving outflow boundary likely to spawn a few more
thunderstorms. Watching closely storms across north Georgia for
possible localized flash flood threat as well. Most storms have been
producing pea to nickel sized hail this evening and expect trend to
continue through 4z to 5z.
Other update was to grids Wednesday afternoon and evening to include small hail
and gusty winds as there appears to be a marginal severe threat
due to slightly increasing deep layer shear
profiles....particularly across northwest and NE Georgia. Will need to monitor
for potentially increasing severe threat after 3 PM Wednesday.
&&
Previous discussion... /issued 805 PM EDT Tuesday may 21 2013/
Previous discussion... /issued 314 PM EDT Tuesday may 21 2013/
Short term /tonight through Wednesday/...
models continue in good agreement through the short term. Airmass
showers/thunderstorms developing across the County Warning Area...mainly across the
extreme north and eastern parts of the County Warning Area. These will dissipate
shortly after sunset this evening. There is a possibility that the
storms over northwest Alabama and central Tennessee could make it to extreme
northwest Georgia before diminishing this evening. The 500 mb ridge over the
eastern U.S. Will weaken as the central U.S. Trough moves into the
Mississippi Valley. This will push a cold front into the Tennessee
Valley Wednesday which will bring a better chance of thunderstorms
to the County Warning Area...mainly across north Georgia. Instability increases Wednesday
across north Georgia and this could produce a few strong storms. Guidance
temperatures look good for tonight...although tricky for Wednesday with
additional clouds. Will trend to the cooler side of guidance across
north Georgia for highs on Wednesday due to increased clouds and precipitation.
17
Long term /Wednesday night through Tuesday/...
by Wednesday evening...both the GFS and European model (ecmwf) indicate that the
front will be weakening significantly. GFS remains ab it on the
strong side with a slightly more east with the Great Lakes surface
low. Both are transitioning the upper low to more of a sharp open
trough phasing with the longwave trough in Canada. Weak shortwave
off the South Carolina coast will lift northeast and be absorbed
by the longwave trough as well. Storm Prediction Center continues the area in general
thunder for Thursday...with MUCAPE values 500-1000 j/kg early in
the day...decreasing by mid-morning...and increasing again in
extreme southern zones just ahead of the front after 18z to over
1000 j/kg. Will have to monitor the area for the potential for
isolated strong storms but nothing to significant.
Cold front should be pushed through the area by late Thursday...
and have decreased temperatures northwest somewhat to line up with that
timing a little better. Should see a significant decrease in temperatures
toward the end of the week with surface high pressure building in
and northwest flow aloft...current forecast has highs on Friday
about 5 degrees cooler than highs on Thursday except in central
Georgia. See previous long term discussion below.
Tdp
Aviation...
00z update...
most of the scattered convection around atl has died down with
sunset...however...outflow boundary which shows up on atl tdwr as
well as boundary on jgx radar near mcn still ingniting a few storms.
Have left ts out for the evening except for atl and mcn which
should get a glancing blow of the cells in East Georgia moving SW. High
res hrrr and WRF indicating some decent storm development around
the metropolitan atl airports between 01z and 02z along the westward
moving outflow boundary but not confident enough in that scenario
to insert into taf...but will monitor for possible amend. Have
introduced prob30 to all taf sites tomorrow afternoon between 19z
and 20z as 4 km WRF showing convective initiation around that time
as weak cold front and remnant outflow move into Georgia. Winds should
go generally calm tonight and pick up out of the south-southwest between 6 to
10kts after around 13z Wednesday.
//Atl confidence...00z update...
medium confidence on convection this evening.
High confidence on all other elements.
Kstellman
&&
Preliminary point temps/pops...
Athens 64 84 64 84 / 30 40 40 30
Atlanta 67 83 66 82 / 20 40 40 30
Blairsville 60 77 60 78 / 30 60 60 30
Cartersville 64 84 62 82 / 20 60 60 30
Columbus 68 89 67 87 / 20 30 30 30
Gainesville 65 83 64 81 / 20 50 50 30
Macon 63 87 65 86 / 20 30 30 30
Rome 64 84 61 83 / 30 60 60 30
Peachtree City 63 85 63 84 / 20 40 30 30
Vidalia 68 89 69 88 / 40 30 30 30
&&
Ffc watches/warnings/advisories...
none.
&&
$$
Short term...30
long term....snelson
aviation...snelson
