Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
1255 am EST Tuesday Dec 1 2015
a back door front slowly slipping south into the region will
stall late tonight and gradually lift back north as a warm front
Tuesday. A cold front approaching from the west will move through
the area Wednesday afternoon and night...followed by cooler and
Near term /until 6 am this morning/...
latest surface analysis indicates leading edge of back door front
stretched across the central forecast area. Fine line return on kcae radar and
surface observation suggest it is very close to Columbia at 2330z...and
still slipping slowly to the south. Trends and latest hi res model
data suggest the boundary will slip a little farther south tonight
and stall. Weak low level wedge will remain in place north of the
front. Best upper energy...moisture and isentropic lift is
expected to remain mainly north. So...probability of precipitation relegated to the
northern forecast area. Will maintain mention of areas of fog for areas south
of the front where lighter winds and possibly less cloud cover
could provide fog potential...mainly southern midlands and csra.
Short term /6 am this morning through Wednesday night/...
axis of deepest moisture shifts north of the forecast area Tuesday
as the cold front to the west slowly pushes into the mountains by
Tuesday afternoon. Extensive stratus clouds and fog possible Tuesday
morning should break up through the day with increasing
southwesterly low level flow ahead of the frontal zone. Little
forcing to support much precipitation during the day Tuesday across
the forecast area although expect scattered showers to continue
along the I-85 corridor and possibly impacting the far northern
midlands so will hold on to some low chance probability of precipitation there but going
with a dry forecast across the southern half of the forecast area.
The upper flow pattern becomes nearly parallel to the orientation of
the surface front which will prevent much movement of it Tuesday
night into early Wednesday. The front will start pushing eastward
Wednesday afternoon...as shortwave energy rounds the base of the
closed upper low across the Ohio Valley...and the front eventually
crosses the area Wednesday night. As the front pushes into the
region Wednesday...precipitable water values surge ahead of the front and rise to
near 1.5 inches on southerly flow. It appears there will be a bit
more instability available as well with forecast lifted index values
around -2c so may add a mention of isolated thunder. Best
convergence along the front and upper forcing remain across the
upstate early Wednesday and shifts northeastward into North Carolina
during the day as the front slides eastward. 850mb flow becomes
westerly quickly as the front approaches and think this will lead to
a more scattered nature to the precipitation and plan to keep chance
probability of precipitation until the front crosses...when probability of precipitation decrease from west to east.
A mild airmass in the warm sector ahead of the front will allow
temperatures to remain well above normal...especially for overnight
lows Tuesday night and highs on Wednesday.
Long term /Thursday through Monday/...
relatively dry weather expected during the extended forecast
period as medium range models and ensembles have come into better
agreement with handling of the potential Gulf low developing along
the stalled frontal boundary.
Thursday morning the cold front will be pushing off the coast as
high pressure builds in from the northwest. A weakening positively
tilted upper trough will cross the region Thursday night and Friday
then push off the coast by Friday night...although both the European model (ecmwf)
and GFS show some sort of upper weakness remaining near the forecast
area beneath a building upper ridge. Nevertheless...time heights
show a dry airmass in place over the region Thursday into the
weekend with precipitable water values dropping below a half inch with slightly
higher values in the csra...and falling to near 0.25 inches by
Friday night into Saturday. A strong gradient in the deeper
moisture will not be very far away...across southern Georgia into
northern Florida. The continual trend of the models to shift the
moisture further south and develop a wave on the front much further
south...will drop the probability of precipitation across the forecast area through the
Another deep trough will move into the western states Sat/sun and
become a closed low and drift into the plains by Sunday night and
Monday. Moisture is expected to return to the forecast area late in
the weekend and may support low probability of precipitation early next week...though
confidence remains low that far out. Temperatures during the
extended period will generally be near normal.
Aviation /06z Tuesday through Saturday/...
conditions rapidly deteriorating across the area with IFR/LIFR
conditions expected through middle morning...then slowly improving to
Ceilings and visibilities have begun quickly decreasing across the taf sites
as fog and stratus develop with the frontal boundary remaining
just north of cae/cub. By 09z expect IFR/LIFR conditions at all
taf sites...-dz will be possible however confidence too low to
include in tafs. With little change in conditions and light and
variable winds fog and stratus will take time to erode after
sunrise with conditions improving to MVFR during the late
morning...and returning to VFR by late afternoon. Next concern
will be potential for fog and stratus after 02/03z...will continue
to monitor and include as confidence increases. Winds through the
period will be southeasterly at 5 knots or less.
Extended aviation outlook...MVFR to IFR fog and stratus are
possible once again Wednesday morning.