Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 212258
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
658 PM EDT Thu Sep 21 2017

.SYNOPSIS...
Surface high pressure will remain in the region through the
weekend. Upper troughing will be over the area through Friday
night, which combined with strong surface heating should help
support scattered thunderstorms. Upper ridging will begin to
push back into the area Saturday and help diminish the
thunderstorm chance.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Weak high pressure at the surface will remain over the region
through tonight along with a weak upper level trough. Scattered
thunderstorms continue across the eastern third of the cwa late
this afternoon, with activity expected to once again diminish
by Midnight. Overnight lows in the upper 60s to near 70. Patchy
fog development possible early Friday morning.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
The models display surface ridging continuing in the region.
Aloft, troughing is depicted with h5 temperatures near -10 C
through Friday night. Some weakening of the trough is forecast
Saturday with temperatures near -9 C. Instability associated
with the upper feature combined with strong surface heating
should help support thunderstorms Friday, but expect limited
coverage because of shallow moisture and the surface ridging.
The thunderstorm chance should further diminish Saturday with
less upper support. The guidance consensus supports pops around
20 percent Friday and less than 20 percent Saturday. Expect
moderate instability Friday afternoon because of the cold air
aloft and strong surface heating with highs in the lower 90s.
The NAM displays surface-based LI values -7 to -8. This
instability plus dry air in the mid levels aiding downdrafts
could help support strong wind with any thunderstorms. Forecast
wet bulb zero heights around 10,500 feet indicates possible hail
as well. The temperature guidance has been consistent with
continued above normal values.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
The GFS and ECMWF display surface ridging continuing during
most of the medium-range period. Some weakening is noted toward
the end of the period ahead of an approaching cold front. The
models also exhibit upper ridging during the period. The pattern
supports a diminished thunderstorm chance with above normal
temperatures. The GFS and ECMWF MOS plus ensemble means support
pops 20 percent or less through the period.

A weakness in the ridging north of Hurricane Maria plus upper
troughing over the Southeast States should steer the storm northward
and well east of the forecast area. The models have been consistent
with this solution. Please see the latest advisory on Maria from the
National Hurricane Center.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Colliding boundaries and some upper level energy may provide
continued impetus for at least isolated convection through this
evening into early tonight. Will maintain VCSH/TS for now.
Otherwise, will expect skies to become mostly clear, with winds
becoming light. Late afternoon dewpoints/crossover temps a
little on the low side in the lower to mid 60s. However, some
precip or outflow cooling may provide some fog potential.
Guidance indicating fog at the fog prone sites AGS and OGB, less
so at the other terminals. Slight chance diurnal thunderstorms
again Friday, chances may be too low to include mention in the
TAFS at this time.

EXTENDED AVIATION OUTLOOK...Late night/early morning
fog/stratus possible, mainly at the fog prone sites AGS and
OGB.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.

&&

$$


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