Scientific Forecaster Discussion
fxus62 kffc 262322
Area forecast discussion
National Weather Service Peachtree City Georgia
622 PM EST sun Feb 26 2017
updated for the 00z aviation discussion.
Previous discussion... /issued 224 PM EST sun Feb 26 2017/
Short term /tonight through Monday night/...
latest rap analysis of the eastern half of the US shows high
pressure centered right along The Spine of the Appalachians
providing for a very light wind flow over the local area. Right
around normal for the temps thus far which for this year is
seasonably cool with mostly upper 50s and lower 60s. Building high
clouds to the west but for the local area it is high and dry.
Speaking of dry...dewpoints remain in the single digits and teens
across a vast majority of the area driving the relative humidity values in the
teens as well with current fire danger statement certainly on
Moisture will be on the increase through tonight and especially
into Monday as high pressure quickly shifts offshore in zonal flow
aloft allowing for good return flow off the Gulf. A warm front
should setup across the deep south in response and act as the
focus along with embedded shortwaves in mid level flow for shower
development west of the area initially.
This activity will eventually translate east to affect northwest Georgia Mon
afternoon although instability axis will remain outside these
areas such that only rain showers are expected at onset. Instability does
build through the late afternoon and into the overnight and have
included slight chance thunder for primarily the southern and
western zones. Confident in categorical pops for northwest zones but much
uncertainty with models on if and how quickly this activity
translates east and south through the overnight period. Have
favored a more progressive solution for now.
Long term /Tuesday through Sunday/...
start of the long-term forecast period brings US to the last day of
February...where the synoptic pattern in the mid levels will feature
long-wave trough over the western US/intermountain west...with a
subtropical ridge parked over the Caribbean. This would leave the
eastern two-thirds of the US in a quasi-zonal/weakly anticyclonic
flow regime. Down at the sfc...strong high pressure centered well
offshore of the Atlantic coast will still have enough ridge
influence over the mid-Atlantic and southeast states...while low
pressure will get spun up over the Central Plains as perturbations
within long wave trough induce cyclogenesis.
Sensible weather will be somewhat disturbed on Tuesday as moist
southerly flow regime promotes persistent warm air advection pattern in the wake of
a warm frontal passage from Monday. GFS/Euro backing off on
quantitative precipitation forecast...but still looks like north Georgia will see at least scattered
showers during the day. Moist boundary layer looks to allow for
enough destabilization for thunderstorms /sub-severe/. Temps will
once again be well-above normal with highs 70s north 80s central
Tuesday afternoon and near 60 Tuesday night.
Wednesday and Wednesday night will be the most interesting periods
of the long-term as a cold front approaches. Storm Prediction Center more aggressive
with 15-30% severe weather outlook across the southeast US/State of
Georgia. Will have to fine tune things the next few days...but
GFS/European model (ecmwf) consistent in bringing a strong shortwave across the
Southern Plains into the Ohio Valley...with associated 90kt+ mid level
jet streak spreading across this area and right entrance region open
to the southeast. At the sfc...continued promotion of high Theta-E air from
Gulf from southerly flow in the warm sector should allow enough
instability develop...despite cooler mid level air displaced to our
northwest. Strong SW flow aloft atop weaker S/SW surface flow should
promote strong deep layer shear /at least 40-70kts/...albeit
unidirectional. All this undoubtedly raises concern for severe
weather...but will have to wait to see if dynamics will actually
line up...which never really seems to be the true case. Strongest
forcing already seems to be displaced a little too far north and
west...but still warrants attention at this Point.
Rest of extended remains dry Thursday-Saturday night under sfc high
pressure and weak northwest flow aloft. Temps should be more "seasonal" in
the 60s during this time. Still evidence of moisture return just
outside of this forecast period as models continue to hint at a
southern stream trough over northern Mexico. Looks like another warm
up as well.
while winds should be much lighter today (generally less than 10 mph)
the low dewpoints should result in afternoon min relative humidity values in the
15-25 percent range area-wide for at least 4 hrs. Given dry
fuels...a fire danger statement has been issued accordingly
no major changes to the previous taf. VFR through tonight and
through most of Monday. Cirrus will increase tonight with mid
level clouds increasing during the day Monday. Lower clouds around
4500 will spread across the region late Monday afternoon with MVFR
cigs moving into the forecast area Monday evening. Scattered
showers will move into the atl/ahn/csg area late Monday afternoon.
Winds will be light southeast to calm tonight...then southeast 5
to 10kts Monday.
//Atl confidence...00z update...
high on all elements.
Preliminary point temps/pops...
Athens 39 67 52 75 / 0 30 40 40
Atlanta 42 65 55 74 / 0 70 50 40
Blairsville 35 57 47 66 / 0 30 50 60
Cartersville 39 61 53 72 / 0 70 40 50
Columbus 43 72 57 80 / 0 30 30 20
Gainesville 40 62 51 70 / 0 70 50 50
Macon 40 74 56 82 / 0 30 40 20
Rome 39 60 52 73 / 0 70 50 60
Peachtree City 38 67 53 76 / 0 50 50 30
Vidalia 45 78 61 84 / 0 30 30 20