Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 191833

Area Forecast Discussion
National Weather Service Columbia SC
233 PM EDT Sat Aug 19 2017

A weak pressure trough will linger east of the forecast area
through Monday. Upper ridging over the region will help keep
moisture shallow and limit the thunderstorm chances. It will
remain hot with heat index values peaking around 100 degrees.


The drier air over the forecast area is evident this afternoon
with generally fair weather cumulus clouds showing up on visible
imagery with the exception of some vertical development in an
area of surface convergence and deeper moisture over the
northern Midlands. Precipitable water analysis shows a pocket of
very dry air with values just over 1 inch in the CSRA and
southern Midlands while values rise rapidly to 1.4-1.5 or
higher just east of the forecast area. There is a tongue of
higher moisture as well across the northern Midlands. Surface
dewpoints have mixed down into mid 60s across much of the area
which is also limiting instability. Regional radar showing most
of the convective activity occurring along the coast and into
far northeast SC and southeast NC where some upper energy is
helping to initiate convection.

Expect only isolated showers and maybe a thunderstorm across the
northeastern Midlands through early evening before instability
wanes and convection diminishes with clearing skies overnight.
The slightly drier airmass along with mostly clear skies
overnight should support slightly lower min temperatures in the
lower to mid 70s. There is the possibility of some fog
development mainly across the eastern Midlands and near bodies
of water due to abundant low level moisture and clear skies with
dry air aloft so added a few hours of patchy fog.


Upper ridging will continue over the region Sunday and
Monday although models indicate some weakness in the ridging
near the coast on Monday. A stalled frontal boundary will
remain near the area through Monday which may be a focusing
mechanism for convection. Moisture will gradually return to the
area from the Atlantic Sunday into Monday. Precipitable water
on Sunday afternoon will generally range from 1.4 inches west
to 1.8 inches east. On Monday, precipitable water values will
increase from 1.6 west to 2.0 east. With the frontal boundary
expected in the central Midlands and higher moisture east,
continued with slight chance pops from the central Midlands
eastward on Sunday. Still believe the better chance for showers
and thunderstorms will be on Monday afternoon with the deeper
moisture returning to the area, so have continued with chance
pops for most of the area. Increased sky cover slightly as
models are bringing in more moisture in the upper levels
particularly in the eastern Midlands. The low-level moisture
increase may lead to patchy fog as indicated by some of the NAM
and GFS MOS during the early morning hours Monday. High
temperatures on Sunday are forecast in the mid to upper 90s
with heat indices around 100. Highs are forecast a few degrees
lower on Monday due to the eclipse and expected increased
clouds, although with higher dewpoint temperatures, heat
indices will still be around 100 degrees.


Surface low pressure will exit the Great Lakes region to
the northeast on Tuesday. This system will bring a cold front
toward the region on Wednesday and the front will move into the
area early Thursday. Surface high pressure centered over the
Great Lakes region will build into the area behind the front
for Friday and Saturday with drier air returning to the area.
Moisture will remain abundant across the area ahead of the
front supporting chance pops Tuesday through Thursday. Lower
pops toward the end of the week behind the front. Lower to
middle 90s forecast for high temperatures Tuesday through
Thursday. Temperatures behind the front for Friday and Saturday
are forecast a few degrees cooler, in the upper 80s.


Mainly VFR conditions expected through the TAF period.

Stalled frontal boundary east of the area along with drier air
aloft over the region limiting convection this afternoon and
do not expect any terminals to be impacted. Mostly sunny skies
through the afternoon with VFR diurnal cumulus clouds which
should dissipate with sunset. Winds will be from the west less
than 10 knots through afternoon then diminish overnight and pick
back up from the east-northeast around 5 knots by 15z.

Some potential for radiation fog development late tonight in fog
prone areas but confidence is low so only included a mention at
OGB/AGS during 09z-12z time frame in a tempo group.

EXTENDED AVIATION OUTLOOK...Scattered mainly afternoon and
evening showers and thunderstorms possible each day. Also,
low-level moisture could result in early morning fog and/or




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