Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 192339

Area Forecast Discussion
National Weather Service Columbia SC
639 PM EST Thu Jan 19 2017

A warm front will move into the region tonight and lift north
of the area Friday. Another warm front will develop and move
into the region Saturday ahead of strong low pressure. The low
will be near the forecast area Sunday and Monday bringing the
possibility of strong thunderstorms to the region.


Upper level ridge axis over our region, stretching north from the SE
CONUS to the E Great Lakes. Upper low over the Cent CONUS with
trough axis extending south through TX.  Surface high pressure and
drier low level air centered along the Mid Atlantic coast nosing SW
into the Carolinas. A weak front stretches from the offshore waters
to our south, NW across GA, to an area of low pressure over W TN.
Resultant S/SW low level flow providing a good tap of moisture and a
large area of showers and a few thunderstorms across the lower Miss
Valley and portions of the Deep South.

Upper energy to our W/NW will shift to the ENE tonight, with main
upper energy appearing to stay just to our N/NW. The front will
shift slowly to the NE as a warm front tonight, appearing to
reach the Savannah River late tonight, and shifting across the
remainder of the forecast area (FA) Friday morning. Model
guidance in good agreement that with the best upper dynamics
will remain just to our north, and also with low level moisture
transport weakening as H85 becomes more westerly, the area of
precipitation to our west will weaken some and decrease in
overall coverage and intensity over our FA late tonight and
Friday morning, with best coverage appearing to stay just to our
NW/N. Latest model runs indicating less QPF late tonight and
Friday morning, around one tenth of an inch or less.

The other possible issue toward morning is fog in the south side of
the warm front. Guidance indicating potential for some fog and low
cloudiness near and to the N of the warm front, mainly favoring
southern portions of the CSRA and Midlands, but confidence of dense
limited at this time.


An enhanced area of isentropic lift associated with warm
advection will be over the forecast area around 12z Friday as a
warm front pushes northeast across the forecast area along with
a weakening upper trough. The highest pops will be early Friday
then decreasing pops through the day with dry weather expected
late Friday through Friday night. Some lower level moisture
will remain over the area Friday afternoon despite the loss of
mid and upper moisture which may support isolated showers with
some daytime heating. Precipitable water values decrease
through the day and 500mb height rises associated with a
building upper ridge support a dry forecast Friday night which
is supported by latest MOS guidance and hi-res models.

Temperatures on Friday will remain well above normal with highs
in the 70s and it should be noted that the MET/MAV MOS has
continued to trend warmer over the past several runs. The only
fly in the ointment could be if lower clouds do not break by
early to mid afternoon. Lows Friday night will be mild in the


Active weather expected over the weekend with the possibility
of some severe weather impacting the forecast area.

Highly amplified 500mb pattern features a northward moving
upper trough over the Northern Plains on Saturday with the
upper ridge over the southeastern states shifting offshore. A
vigorous shortwave moving across the desert southwest will
emerge over the Southern Plains as a closed low with a surface
low developing over Oklahoma Saturday night. Expect another
surge in atmospheric moisture Saturday afternoon and night over
the forecast area with precipitable water values increasing to
near 2-3 standard deviations above normal and values well over
1 inch. There are indications of some available instability
combined with increasing shear (NAM more impressive than GFS)
during peak heating Saturday which could support some
thunderstorms and isolated severe potential. Will continue to
highlight likely to categorical pops late Saturday and Saturday

There is some uncertainty among the model guidance by Sunday
regarding the location and movement of the surface low pressure
system and the associated upper trough/closed low. The NAM is
much stronger in deepening the surface low across TN and
lifting it into central KY Sunday afternoon and brings very
strong low level shear over the forecast area (850mb winds
50-60 knots) along with significant instability with LI values
-6C to -8C. This appears to be a  bit of an outlier at the
moment as the GFS/ECMWF/CMC are weaker with the surface low and
track it further south along with a further south track of the
upper low moving it over our forecast area Sun night into
Monday. This scenario keeps the strongest shear a bit further
south across southern GA and northern Florida and along the SC
coastal plain and instability is not quite as unstable with LI
values around -4C to -5C.

Despite the uncertainty of the guidance it appears possible
that we could have severe weather over the weekend and we will
continue to monitor forecast trends. The most favorable time
frame for severe weather at this time appears to be late
Saturday through Sunday evening (but not likely the entire
period, just sometime within that window). SPC has the area
outlooked in general thunder with a marginal risk in the CSRA
Sat/Sat night and slight risk on Sunday.

The upper low will cross the region on Monday and depart to the
northeast by Monday night with quiet weather expected Tues/Wed
as surface high pressure builds over the region and weak
shortwave ridging moves overhead. Another digging upper trough
across the Northern Plains/Midwest will push a cold front into
the area sometime Wednesday night or Thursday bringing another
increased chance for rain. Temperatures will remain above
normal throughout this period.


VFR conditions to continue this evening with high clouds over
the region lowering to mid level around 04z.

Showers will start moving into the area from the west along a
warm front after midnight. High confidence for cig/vsbys
restrictions 08Z-17Z. There are some questions on the timing
depending on the model you believe, so continued a similar
start time at all terminals.

Both MET and MAV guidance indicating IFR/LIFR 10Z-16Z. Should
see conditions improving to VFR early Friday afternoon as the
warm front lifts north of the area and southwest winds increase
to around 10 knots.

EXTENDED AVIATION OUTLOOK...Showers...and associated restrictions...
are likely Saturday through Monday as a low pressure system
crosses the region.




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