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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCAE 181824
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
224 PM EDT Fri Aug 18 2017

.SYNOPSIS...
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A weak frontal boundary will cross the area overnight and stall
over the Coastal Plain through the weekend. Drier air will work
into the region providing dry weather Saturday and Sunday for
much of the region except the eastern Midlands. Moisture will
increase again early next week as an upper ridge builds back
over the southeastern states.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Atmosphere is a bit more stable today compared to yesterday due
in large part to lower atmospheric moisture. Precipitable water
values are quite a bit lower this afternoon around 1.6-1.7
inches compared to Thursday when they were over 2 inches. A
subsidence inversion around 700mb was evident on HRRR forecast
soundings and current visible imagery showing generally fair
weather flat cumulus clouds across the forecast area. Some
enhanced cumulus noted over eastern TN into the mountain of NC
associated with shortwave energy lifting into the Mid-Atlantic
region but that should remain north of our area.

Hi-res model guidance continues to show minimal convection over
our area through early evening with some storms possibly
developing on the front that is approaching from the west during
the evening and overnight hours through 06z but mainly focused
across the northern Midlands. Will hold on to slight chance pops
through the afternoon and chance pops in the northern Midlands
this evening before diminishing pops overnight with the loss of
daytime heating. Storms that do develop will have the potential
to produce strong gusty winds with significant dry air aloft and
downdraft CAPE values at or above 1000 J/kg. Skies should clear
late tonight behind the front with winds turning more
northwesterly albeit light. Overnight lows expected in the mid
70s with some patchy fog possible in the eastern Midlands where
moisture may pool a bit ahead of the weak front.
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&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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A weak cold front will stall over the area on Saturday. However,
it should be mostly dry as the models have more significant
moisture shifted farther east ahead of upper troughing, with
little recovery Sunday because of a building ridge. Mid-level
temperatures are forecast to remain relatively warm and dry with
h5 temperatures around -5 C. There will be a capping inversion
that will limit instability and thunderstorm coverage. The
slightly drier air should also result in lower heat index
values. However, it will remain hot with forecast maximum heat
index readings 100 to 105.
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&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
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The models show upper ridging building over the region Monday
as surface high pressure strengthens over the western Atlantic.
Low-level moisture will increase due to a southeast flow off
the ocean. The pattern supports partly cloudy skies with a
chance of mainly afternoon thunderstorms. Thunderstorms will be
most likely across the CSRA and southern portions of the
forecast area. Areas north and west of Columbia will have lesser
chances. Similar weather is expected Tuesday. Another weak cold
front is forecast to approach Wednesday and be in the area
Thursday which will bring an increased chance of thunderstorms.
The GFS and ECMWF MOS have pops 20 to 30 percent Monday and
Tuesday, and 30 to 40 percent Wednesday and Thursday. The MOS
supports above normal temperatures lowering to about normal
Thursday. Drier westerly flow is expected Friday. Expect
maximum heat index values 100 to 105 through the period.
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&&

.AVIATION /18Z FRIDAY THROUGH TUESDAY/...
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Generally VFR conditions through the period.

Diurnal cumulus clouds will blanket the are this afternoon with
isolated showers or thunderstorms developing along a weak
frontal boundary crossing the region this evening. Coverage is
widely scattered with low confidence in any terminal being
affected so not including in the forecast at this time. Winds
will be from the southwest 5 to 10 knots through 00z then
diminish to less than 5 knots and become light and variable
overnight. Winds will pick up from the west around 5 knots after
15z with some diurnal cumulus clouds developing by the end of
the forecast period.

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 stratus.
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&&

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

&&

$$