Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
624 am EST Thursday Dec 18 2014
Previous discussion... /issued 336 am EST Thursday Dec 18 2014/
Short term /today through Friday/...
upper level feature in the zonal flow aloft has ushered moisture
into the region this morning...mostly seen in increasing cloud
cover. Models continue to suggest that as the middle levels
moisten...the main wave feature could produce some light rain
showers in the far northern zones...particularly late morning into
early afternoon. Models /including the hi-res solutions/ have backed
off on the southern extent of the precipitation...and have followed suit in
the probability of precipitation...with only brief slight chance probability of precipitation centered around noon.
Will still see the impact of this feature in cloud cover...with
generally partly to mostly cloudy skies across the state.
Expect gradient in high temperatures today as a result of the ample
cloud cover...with only highs in the upper 40s north...and low to
middle 60s south. MOS guidance...particularly for dew
points...continues to be the outlier...and have trended more towards
the NAM/met for highs and dew points through the short term.
Rain chances return late in the short term as next system approaches
the state and impacts the region through the initial periods of the
extended forecast. Based on the track of the system...models suggest
rain will move in from the southwest...with slight chance probability of precipitation
beginning early evening Friday...and expanding and increasing
overnight Friday. For now...have continued with no mention of
Long term /Friday night through Wednesday/...
spell of dry weather to end beginning this weekend and next week. Flow
over most of Continental U.S. To become more zonal Friday. Model forecasts in
good agreement on shortwave over Southern Plains to move east to MS
River Valley Friday night. Solid warm/moist advection pattern kicks
in well in advance of wave. Based on track of wave...rain chances
appear categorical Friday night and Sat morning. Have bumped probability of precipitation up
from model consensus blend. Wave fairly open so zonal flow and no
strong subsidence or surface ridging behind it. Could be good pattern
for stratus...fog and drizzle if we get overrunning. Kept slt chance
probability of precipitation going for measurable drizzle or light rain Sat night through Sun
Pattern becomes more amplified over Continental U.S. As strong flow digs into
large trough over the plains. First in a series of short waves to
lift east-northeast along Gulf Coast out of south Texas Sun night. Models have a
little higher rain chances Monday middle Georgia and points south and
east as wave quickly lifts and dampens. Again...southwest flow in
wake of this wave so even better opportunity for fog/drizzle Monday
Tuesday...large upper trough with low centered over Iowa. Lobe of
vorticity over western Tennessee to lift NE then north over Midwest states.
Timing and location of upstream wave will be key to precipitation...both
intensity and type on Tuesday night through Wednesday night /xmas eve/. 00z
European model (ecmwf) coming more in line with previous GFS runs and other medium range
models with main upper low remaining over Midwest states and
somewhat less sharp trough axis than previous ec runs...moving into
middle-south Tuesday night. Main threat if any Tuesday night could be high-
shear Low-Cape storms but likelihood of that diminished from previous
ec runs. Dry slot should end precipitation quick Wednesday but some very light
rain showers or even snow showers poss in far north Georgia as very
cold air aloft rotates through Wednesday and Wednesday night. Again...00z ec
backing off on amount of cold air and upper low formation further
south. Did keep small chances of light rain/snow showers in forecast
mainly in higher elevations. No real chance for any precipitation in atl
metropolitan or middle Georgia after 12z Wednesday. Will continue to monitor.
although MVFR visibilities are possible through 14z...in general...VFR
conditions expected through the period. Middle-level clouds increase
by late morning...then diminish overnight with high level clouds
prevailing. Northwest winds of 7kt or less through the period may flirt
with due north or possibly north-northeast briefly late morning.
//Atl confidence...12z update...
high confidence on all elements.
Preliminary point temps/pops...
Athens 57 35 56 41 / 0 0 5 70
Atlanta 55 37 55 44 / 0 0 10 70
Blairsville 52 31 52 38 / 10 0 5 70
Cartersville 52 30 53 40 / 5 0 10 80
Columbus 61 40 60 47 / 0 5 30 80
Gainesville 55 36 53 41 / 5 0 5 70
Macon 61 36 61 44 / 0 0 20 70
Rome 51 30 52 39 / 5 0 5 80
Peachtree City 58 32 56 42 / 0 0 20 70
Vidalia 63 41 63 48 / 0 0 20 50