Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 201046
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
646 AM EDT Sun Aug 20 2017

.SYNOPSIS...
A weak pressure trough will linger in the forecast area through
Monday. However, upper ridging over the region will help keep
moisture shallow and limit the thunderstorm chance. It will
remain hot with heat index values peaking around 100 degrees.

&&

.NEAR TERM /THROUGH TONIGHT/...
A weak surface pressure trough will remain in the forecast area
through tonight. Strong heating and convergence into the trough
supports thunderstorms but expect little coverage because of
shallow moisture and upper ridging. The NAM and GFS MOS have
pops less than 20 percent. The high-resolution models indicate
isolated coverage. We kept pops less than 20 percent. An
increase in low-level moisture in a southeasterly flow with
continued dry air aloft supports at least patchy fog late
tonight as indicated by some of the NAM and GFS MOS plus a
significant number of SREF members. The temperature guidance was
close. Expect maximum heat index values around 100 this
afternoon.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
An increase in low-level moisture in an onshore flow plus
convergence into a lingering weak surface trough should help
cause at least scattered cumulus clouds during much of the day
Monday. There will be areas of more cloudiness and possibly
thunderstorms but believe these will be limited because of upper
ridging. Greater cloudiness and thunderstorm chances may be in
the southeast section closer to deeper moisture and a weakness
in the h5 ridge near the coast. We followed the guidance
consensus pop of near 20 percent northwest to 30 percent
southeast. The temperature guidance has been consistent. Expect
highs in the lower 90s with maximum heat index values around
100.

The thunderstorm chance should further diminish Monday night
with the loss of heating and upper ridging. Tuesday will likely
be similar to the previous day. Expect thunderstorms mainly
associated with low-level moisture in an onshore flow plus
strong heating and convergence into a weak surface trough. Upper
ridging should continue to limit coverage and the guidance
consensus supports pops around 30 percent. Heat index values are
forecast to peak 100 to 104.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
A cold front will approach Wednesday. Strong heating and
convergence into a prefrontal trough supports thunderstorms
mainly in the afternoon. The GFS and ECMWF MOS have pops 30 to
50 percent. The thunderstorm chance will continue Wednesday
night and Thursday with the front in the area. The MOS has pops
around 40 percent. It may be drier with the front just off the
coast Friday and Saturday, but confidence is low with the front
lingering not far to the east. We kept a small chance in the
east section. Temperatures should remain above normal ahead of
the front through Wednesday. Expect maximum heat index readings
100 to 105 Wednesday afternoon. The GFS and ECMWF MOS support
near normal temperatures Thursday through Saturday.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
Mostly clear skies and light winds may allow some localized
early morning ground fog/stratus at OGB and AGS. Otherwise,
expect VFR conditions through the forecast period with upper
ridging limiting the thunderstorm chance.

EXTENDED AVIATION OUTLOOK...Scattered mainly afternoon and evening
showers and thunderstorms Monday through Thursday, with increasing
chances each day. Also, low-level moisture could result in early
morning fog and/or stratus.

&&

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

&&

$$



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