Area Forecast Discussion
Issued by NWS Columbia, SC
FXUS62 KCAE 310222 AAA
Area Forecast Discussion...UPDATED
National Weather Service Columbia SC
1022 PM EDT TUE AUG 30 2016
Daytime heating and an onshore low-level flow expected to result
in scattered showers and a few thunderstorms through Wednesday,
favoring areas closer to the coast. A tropical cyclone is forecast
to develop in the Gulf of Mexico and move NE across North Florida
and offshore the Carolina coast mid to late week. Behind the
cyclone, drier and cooler high pressure will build into the region
for the weekend.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Afternoon convection has diminished with only some lingering high
level clouds remaining over the forecast area late this evening.
Any precipitation should remain near the coast overnight and
expect dry conditions. Low confidence in stratus development late
tonight despite plenty of low level moisture in place with
persistent easterly flow off the Atlantic. Overnight lows will be
mainly in the lower to mid 70s.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
A surface and upper level low remains near the coast Wednesday.
The air mass across the region remains moist and weakly to
moderately unstable as east-northeast moisture advection
continues. Precipitable water near 2 inches in the east Midlands
and lower CSRA...drier air in the Piedmont. Weak short wave
troughs rotating around upper level low may trigger scattered
showers and thunderstorms at times...mainly in the afternoon
during peak heating...although overall upward lift appears weak.
Highest pops in the east. Despite considerable low-level moisture
expect temperatures to rise to at least guidance values...near 90
Tropical depression 9 in the southeast Gulf of Mexico
this afternoon expected to strengthen later today and track north
and northeast toward the northern west coast of Florida by
Thursday afternoon. The storm is expected to move across the
Florida peninsula to southeast of Savannah GA Thursday night. Some
strengthening possible off the coast of GA/SC but increasing shear
should limit development. The track guidance is supported by the
global models and High resolution tropical cyclone models.
However...the latest GFS is a little further west than the other
models and its previous run...which poses a higher threat for
South Carolina. Upper level long wave trough over the Northeastern
States and Mid Atlantic will be amplifying and a cold front will
be approaching SC late in the day Thursday. This trough should
steer tropical cyclone to the east. Timing of the front may be
critical to cyclone track. With the consensus guidance keeping
cyclone well offshore...although coastal SC remains in the error
cone...overall threat for Midlands and CSRA remains low.
Expect only isolated showers or thunderstorms early Thursday
through mid day...increasing diurnal convection in the afternoon
with peak heating...although moisture flux from the coast appears
to weaken and some drier air expected across the area. Went a
little warmer than Wednesday due to possibly less clouds. Cold
front approaches the area Thursday evening moves through overnight
or Friday morning. Scattered to numerous showers along the front
although timing at night may be limiting factor for strong
convection/instability weak to moderate/shear weak. Tropical
storm moving northeast along the coast. Ensembles support highest
pops during this period although uncertainty remains. Overnight
temperatures through the period near guidance...in the 70s.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
The tropical storm should continue tracking northeast. Expect
drying developing from west to east Friday afternoon. Note models
indicate dew points in the 50s over the weekend.
Generally went with a blend of guidance. From Friday night
through the weekend...it appears drier and cooler air will work
into the region behind the exiting tropical system. High pressure
centered over New England will nose down the Appalachians and into
the region through Monday. Uncertainty past Monday/Tuesday. ECMWF
shows an area of low pressure developing on the old frontal
boundary off the Carolina coast Monday night into Tuesday, whereas
the GFS keeps ridging across the region. Would expect to see a
return of diurnal precip chances as we get into the middle of next
week. Temperatures remaining close to normal.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Surface troughing will continue just off the southeast coast.
Weak upper troughing will remain along the coast. Deepest
moisture will be east of the terminals closer to the troughing.
The pattern supports scattered showers and thunderstorms with
greater coverage associated with diurnal heating. Thunderstorms
were not included in the terminal forecasts at TAF issuance
because of the scattered coverage and timing uncertainty. High
low-level moisture and nocturnal cooling may result in stratus and
fog during the early morning hours. We followed the GFS LAMP and
forecasted MVFR fog at the river valley terminals of AGS and DNL.
Heating and mixing should dissipate any fog around 14z.
EXTENDED AVIATION OUTLOOK...Widespread IFR or MVFR conditions may
occur Thursday and Friday associated with a cold front moving
into the area from the northwest. There may also be added
moisture associated with a tropical system forecast to move
northeastward off the southeast coast during this period.