Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 171114

Area Forecast Discussion
National Weather Service Charleston SC
614 AM EST Thu Jan 17 2019

Dry high pressure will prevail today with a weak upper
disturbance moving through tonight. A stronger storm system
will then impact the area Saturday night and Sunday. Much
colder temperatures will return early next week followed by
increasing temperatures and rain chances into the middle of
next week. 


As of 610 AM: I will issue a quick update to cool morning
temperatures to recent observations. The patchy fog across the
area is still anticipated to dissipate within an hour following

As of 4 AM: A slight surge in high pressure is expected to push
over the Charleston Tri-county region around daybreak this 
morning. As a result, surface winds are expected to shift out of
the north, possibly resulting in an increase in moisture 
convergence. I will include a mention of patchy fog across 
portions of Dorchester, Berkeley, and Charleston Counties. The 
fog should dissipate within an hour following sunrise. As the 
center of low pressure tracks over the Ohio River Valley, llvl 
winds are forecast to shift from the south-southwest. The 
combination of return flow and at least partly sunny conditions 
should allow temperatures to peak in the low to mid 60s. 

Tonight: The center of low pressure will continue to track to the NE 
across the mid-Atlantic states. The associated cold front is 
forecast to sweep across the southern Appalachians between 9Z to 
12Z. Within the mid-levels, a weak short wave will ripple across the 
forecast area this evening, well ahead of the sfc cold front. High 
resolution CAM guidance indicates only a few showers will be 
possible tonight, supporting only SCHC PoPs across the SC 
Lowcountry. Given thick clouds and continued SW winds, low 
temperatures should verify in the mid 40s.


Generally high confidence this period. Surface high pressure will 
maintain mainly dry conditions Friday although a few showers cannot 
be completely ruled out toward the CSRA where moisture and 
instability will be increasing a bit. A warm front is expected to 
develop over or near the area Friday night ahead of low pressure 
near Texarkana and this could lead to a few showers into Saturday, 
mainly well inland, but it looks like the bulk of the rain will hold 
off until Saturday night with clearing on Sunday. Still appears 
instability will remain low as thus the risk for thunderstorms as 
well. Rain amounts still look to average around a half inch with 
some locally higher amounts. Temperatures will be well above normal 
through Saturday (when it could get near record highs especially at 
KSAV), then return back to near normal Sunday (although highs are 
more likely to occur earlier in the day due to the cold advection 
kicking in during the day behind the front). It will also become 
breezy Saturday afternoon and continue through Sunday with a Lake 
Wind Advisory possible for Lake Moultrie starting Sunday.


High forecast confidence through Monday night before confidence 
lowers into mid week. High pressure will be building from the 
northwest behind an upper trough pushing offshore to start the 
period. The high should be centered near NC/VA by Tuesday with a 
coastal trough developing off the Southeast U.S. coast. Thereafter 
the forecast becomes more uncertain as some model guidance is more 
progressive with the high shifting offshore than others, but for now 
we trended toward the slower ECMWF solution which matches better 
with the GFS ensemble mean. So we are indicating small rain chances 
returning Tuesday night and increasing Wednesday before diminishing 
behind a cold front into Thursday. 

Most, if not all, locales should be below freezing Monday morning 
with inland areas in the mid to upper 20s and wind chills near 20 
degrees. It's not out of the question that coastal areas reach Wind 
Chill Advisory levels of 15 degrees, especially near Charleston 
where the colder temperatures are expected. Highs Monday should only 
range from around 40 near the Santee River to 50 near the Altamaha 
River. Temperatures Monday night look a bit milder especially near 
the coast due to more onshore winds but interior areas could reach 
similar temperatures as Monday morning. Thereafter temperatures will 
moderate into mid week to near or above normal levels before 
possibly returning back below normal again Thursday behind the cold 


Near term guidance indicates that sfc high pressure will surge
southward across KCHS around dawn this morning. Latest
observation around KCHS indicate patchy fog. Moisture 
convergence is expected to increase and will support a period of
patchy fog. I will include a TEMPO between 12Z to 13Z for BR. 
KSAV should remain VFR. During the daylight hours, south winds 
will develop within the warm sector of low pressure tracking 
across the Ohio River Valley. Winds across the terminals will 
become light southwest to calm during the evening hours.

Extended Aviation Outlook: Restrictions possible as early as Friday 
but more likely Saturday night into early Sunday, probably IFR or 
worse at times due to low clouds and moderate rain. Also, 
breezy/gusty conditions are expected later Saturday into 
early Monday.


Today and tonight: Broad high pressure will remain centered over FL 
as a cold front crosses the southern Appalachians late tonight.
Winds are forecast to range between 5 to 10 kts south during the 
daylight hours. Winds should shift from the west and increase to 10-
15 kts. Seas are forecast to remain around 1 ft across the near 
shore waters and 2 ft beyond 20 NM. Tonight, seas will generally 
remain unchanged, possibly occasional 3 ft waves across the outer GA 

Friday through Tuesday: No concerns through Saturday (although there 
is a low risk of sea fog developing Saturday/Saturday night over the 
nearshore waters), but conditions will be deteriorating 
significantly Saturday night and Sunday as a strong cold front 
affects the area with some heavy showers and possible thunderstorms 
(mainly near the Gulf Stream). Wind could even gust near gale force 
across the GA waters beyond 20 nm Saturday night into early Sunday 
night. Otherwise, Small Craft Advisories are expected for the entire 
area. Should see improving conditions Monday as winds turn offshore 
and diminish with the weakening cold air advection.


Tides/Coastal Flooding...Astronomical tide levels will be high early 
next week and strong north/northeast winds will help contribute to 
even higher levels which could lead to minor saltwater flooding 
around high tide, especially starting Monday. Thus, Coastal Flood 
Advisories will be possible.