Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 191525 AAA

Area Forecast Discussion...UPDATED
National Weather Service Columbia SC
1125 AM EDT Sat Aug 19 2017

A weak pressure trough will linger in the forecast area through
Monday. 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.


The surface boundary that crossed the forecast area on Friday
has stalled near or just east of the forecast area. Precipitable
water values have lowered significantly since yesterday to
around 1.3 inches as noted on SPC mesoanalysis page and
confirmed by GOES16 derived PW plot. There remains a strong
gradient in deeper moisture over the eastern Midlands to the
Coastal Plain and this figures to be where convection may
develop this afternoon. There is an area of higher moisture in
the Pee Dee region with some low level convergence is possible
this afternoon and may support isolated showers or thunderstorms
as well.

Forecast instability is weak to moderate but moisture is shallow
and forecast soundings indicate a weak capping inversion. Mid
level temperatures remain warm with 700mb temps at +10C and
500mb temps around -4C to -5C so there are many limiting factors
for convection today. Will continue to advertise slight chance
pops mainly in the Pee Dee and along the far eastern Midlands
this afternoon into early evening. High LCL heights and plenty
of dry air in the mid levels support possible gusty winds with
any storms that develop.

Temperatures are running a few degrees cooler than at this time
Friday but with plenty of sunshine expect max temperatures to
again be hot in the mid 90s across the area with some upper 90s
also possible. Deep mixing with drier air aloft will help mix
out the dewpoints a bit more helping to keep heat indices below
advisory criteria in the 100-104 range.


The models show upper ridging building Sunday and continuing
Monday but some weakness in the ridging near the coast Monday.
Some surface troughing is indicated lingering in the forecast
area. More of an onshore flow with a little increase in
moisture is depicted Monday. The pattern indicates skies mostly
sunny Sunday and partly cloudy Monday. The guidance consensus
supports pops around 10 percent Sunday, and 20 to 30 percent
Monday. The chance may be greatest in the southeast section
Monday with more of a moisture increase in the flow off the
Atlantic. 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. The temperature guidance has been
consistent. Temperatures Monday should be a little lower because
of increased cloudiness and the eclipse. However, heat index
values will likely be about the same both Sunday and Monday.
Expect maximum values around 100.


Moisture associated with the flow off the Atlantic should
continue Tuesday. The models depict a weakness in the upper
ridging but still have relatively warm air in the mid levels
with h5 temperatures -5 to -6 C. The guidance consensus supports
pops around 30 percent. A weak cold front is forecast to
approach Wednesday and be in the area Thursday which will bring
an increased chance of thunderstorms. The guidance consensus
supports pops around 40 percent. The front and associated
moisture may be off the coast for Friday. The guidance has pops
lowering to around 20 percent. The MOS supports above normal
temperatures lowering to about normal for Thursday and Friday.
Expect maximum heat index values 100 to 105 through Wednesday
with somewhat lower values during the rest of the period.


Mainly VFR conditions expected through the TAF period.

Stalled frontal boundary east of the area along with drier air
aloft over the region should limit convection today and what
does develop should be east of the terminals so no mention in
the forecast. Mostly sunny skies into early afternoon then
diurnal cumulus will develop with VFR ceilings. Winds will
be from the west less than 10 knots.

Some potential for radiation fog development late tonight in fog
prone areas but confidence is limited at this time.

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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