Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 210238

Area Forecast Discussion
National Weather Service Columbia SC
1038 PM EDT Sun Aug 20 2017

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 chances. Expect
above normal temperatures through Wednesday with heat index
values peaking around 100 degrees. A cold front will push into
the region mid-week bringing a high chance for showers and


Regional radars continue to show isolated showers across the
Piedmont just west of the cwa. May see some clearing of clouds
overnight, but some higher clouds associated with an area of
disturbed weather off the east coast of Florida could advect
northward over the area late tonight. Despite the moisture in
the lower levels and drier air aloft which may favor some fog
formation, the arrival higher clouds may limit radiational
cooling so confidence is limited in fog development, though it
is possible especially across the eastern half of the forecast
area. Overnight lows will be in the mid 70s.


Increasing low level moisture in onshore flow will allow for
cumulus clouds to develop during the day Monday. Confidence is
high that the greatest cloud coverage will be in the eastern
Forecast Area (FA) with less cloud coverage in the western FA.
However models depict a large spread in the amount of cloud
coverage. In general expect scattered to broken cloud cover
across much of the FA. Mid-level ridging and dry air will
inhibit deep convective development and keep PoP chances from
slight in the western FA to low chance in the eastern FA.

High temperatures Monday will be in the low to mid 90s with heat
index values around 100 degrees. Temperatures are expected to
have a brief dropoff in areas experiencing the total eclipse,
with the temperature rebound lagging for about an hour after
totality ends.

The chance for showers and thunderstorms will diminish Monday
night with the loss of heating and upper ridging. Lows will be
in the low to mid 70s.

Tuesday will be similar to the previous day with increasing low-
level moisture in onshore flow. Strong heating and convergence into
a weak surface trough will produce scattered thunderstorms in the
afternoon. Upper ridging should continue to limit coverage and
updraft strength. Expect above normal temperatures to continue.


A cold front will approach the region mid-week. Warm advection
and convergence into a prefrontal trough will support
thunderstorms Wednesday afternoon through Thursday. During this
time, model guidance has been consistently suggesting PoPs
ranging from 30 to 50 percent. Kept a high chance of showers and
thunderstorms from Wednesday afternoon through Thursday given
the uncertainty in the timing of the front. The front should
push through the forecast area on Friday bringing in drier air
for the remainder of the period. However added a slight chance
of showers and thunderstorms towards the end of the long term
given the possibility the front will drift back to the north.
Temperatures will be above normal through Wednesday. Near
normal temperatures expected following the frontal passage.


VFR conditions expected through early tonight. In the near term, a
sea breeze boundary, seen on radar penetrating inland, will maintain
a SE wind at our TAF sites through late evening. Low levels are
slightly more moist than at this time yesterday, with late afternoon
dewpoints/crossover temps a few degrees higher. A SE boundary layer
wind overnight may provide some stratus potential late tonight into
early Monday morning. Some fog possible as well, though less
confidence given uncertainties with regards to upper level
convective debris cloud cover streaming up from the south. Most
guidance indicating some restrictions, more likely to the east and
south. For now, will indicate MVFR at CAE/CUB/DNL, with IFR at the
farther south and also most fog prone locations, AGS and OGB.  After
morning fog/stratus, expect VFR Monday. A SE wind and a gradually
moistening atmosphere will provide a slight chance of afternoon
convection. At this time, it appears the better chance will be
towards the south and mainly late in the afternoon.  For now, will
lean optimistic and only indicate VCSH at OGB after 18Z.

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.




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