Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Peachtree City Georgia
744 am EDT Monday Mar 17 2014
Previous discussion... /issued 404 am EDT Monday Mar 17 2014/
Short term /today through Tuesday/...
guidance remains in pretty good agreement on the synoptic pattern
for the short term...with deep negatively tilted upper trough
pushing across the deep south today while a surface low over Alabama
dives southeast across Georgia and toward the coast through the
day...as a strong cad event builds in from the northeast. As always
however...the devil is in the details where there are some more
So lets talk about temperatures first. As far as verification
numbers go...yesterday worked out pretty darn well as mav was too
warm...met was too cool...so the blended approach was definitely the
way to go. Mav continues on the warm side through the short term...
running about 5 degrees warmer than the met. Of course this will be
highly dependent on the location of The Wedge front. The 00z GFS
holds off on building the cold dome into Atlanta until later today
/hence the warmer temps/...and with that the surface low track is
initially just north of the city...then east...finally diving south
toward the coast. The 00z NAM on the other hand really barrels The
Wedge front southwest this morning /hence the cooler temps/...
forcing the surface low to stay on the west and south side of the
metropolitan area. Taking a blend of the two it may very well likely be
that The Wedge front just remains over the metropolitan Ara. So without any
reason to go against it...again took a blend through the short
term...pulling back on bias-corrected values. In the cold dome...
highs will be several degrees below seasonal averages. Of course the
uncertainty in location of The Wedge front has frustrating
implications on winds but that is more of an aviation concern than
anything...but may mean the difference between west-southwest winds
/outside of the cold dome per the GFS/ or east winds /per the NAM/.
Eventually the cad will become firmly entrenched and winds will all
be out of the east.
If the temperatures and winds weren't interesting enough...add the
complication of probability of precipitation and weather. The widespread rain from yesterday
has pushed south and east but there is still quite a bit of
moisture in place and with the approaching upper/surface
systems...plenty of synoptic scale lift as well. Model soundings
do show some weak elevated instability and showers moving across
north Georgia this morning have intermittently worked all the way
up to 50dbz...so would not be surprised to hear a few rumbles of
thunder in there. Storm Prediction Center only has general thunder through 12z this
morning and nothing thereafter but again just cannot rule out some
rumbles here and there. No real hazards expected aside from brief
heavy rain though. So what we are looking at is in addition to the
more stratiform rain currently across portions of south and
central Georgia...expect continued regeneration across north
Georgia with increasing positive vorticity advection aloft. As the surface low works its
way south and east...probability of precipitation across north Georgia will begin to taper
off today but kept likely across central zones through tonight. A
lot of low clouds and intermittent fog issues but not really
expecting much in the way of dense fog at least not widespread
with strong winds just off the surface helping to keep that
boundary layer mixed.
Long term /Tuesday night through Sunday/...
Short and long range models continue to show a moist south to southwest
middle level flow producing a few patches of light rain or drizzle
across parts of north Georgia Tuesday night. Then the long range models
continue to agree on a weak cold frontal passage by middle week. This
will warrant a low chance of probability of precipitation across mainly north Georgia on Wednesday.
Although the GFS is still slightly faster with this frontal passage... both
European model (ecmwf) and GFS show high pressure and dry conditions for Thursday
and Friday. Long range models show good agreement on another cold
front pushing across the area on Saturday... with the GFS showing
slightly more moisture and quantitative precipitation forecast with this system. Will continue to show
a chance of showers on Saturday...but no thunder is still
warranted as both models agree on weak upper support and nearly
none instability. A cool dome of high pressure builds in for Sunday.
generally IFR through the period with only brief improvement
possible at csg later today. LIFR ceilings for northern tafs this
morning. Winds generally east at northern tafs...SW initially at
csg/mcn but going east for those sites as well this evening.
Intermittent -shra mainly this morning and early afternoon.
//Atl confidence...12z update...
low on occurrence of thunder.
Medium on all other elements.
Preliminary point temps/pops...
Athens 48 37 49 42 / 70 50 30 20
Atlanta 54 38 53 45 / 70 40 20 10
Blairsville 48 37 52 41 / 60 40 20 20
Cartersville 54 39 56 44 / 60 40 20 10
Columbus 63 44 60 45 / 80 50 30 10
Gainesville 46 37 48 43 / 60 40 20 20
Macon 61 42 54 43 / 80 60 30 10
Rome 53 41 59 46 / 60 40 10 10
Peachtree City 56 39 54 41 / 70 50 20 10
Vidalia 60 45 55 47 / 90 70 50 10