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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 161238

Area Forecast Discussion
National Weather Service Charleston SC
738 AM EST Wed Jan 16 2019

Dry high pressure will build from the west and prevail into
Thursday. A weak cold front will approach the area Friday, then
lift north as a warm front Saturday. A stronger storm system
will then impact the area Saturday night and Sunday with much
colder temperatures to follow starting Sunday night. 


As of 630 AM: Thin cirrus has started to stream across the
forecast area, sourced from the Mississippi Delta region. I will
update the forecast to slightly increase the sky cover.

As of 550 AM: Stratus has begun to decrease from west to east,
as previously expected. The combination of clearing sky, light
to calm winds, and narrow dewpoint depressions has resulted in
patchy fog early morning across portions of Colleton,
Dorchester, and Berkeley Counties. I will update the forecast to
add a mention of patchy fog until sunrise.

As of 330 AM: Early morning stratus across the coastal counties is 
forecast to slide over the coastal waters prior to sunrise. It 
is possible that patchy fog could develop under the clearing sky
over the CHS Tri-county. For the rest of the day, the sfc 
pattern will feature weak ridging high pressure along the coast 
with the lee trough across the western Carolinas. Within the mid
levels, a long wave ridge axis will ripple across the central 
CONUS, resulting in slight rises across the forecast area this 
afternoon. The pattern will result in nearly steady H85 
temperatures and LLVL thicknesses. Given sunny to mostly sunny 
conditions and light west winds, high temperatures are forecast 
to range from the upper 50s across the CHS Tri-county to near 60
degrees along the Altamaha River.

Tonight: Broad high pressure will spread across most of the East 
Coast, centered over the Great Lakes Region. The shallow mid level 
ridge axis is expected to peak across the CWA during the pre-dawn 
hours. I will indicate calm winds across the SC Lowcountry and SE 
GA, just ahead of surging high pressure. Forecast soundings indicate 
that most of the night will remain clear, with thin cirrus possible 
during the late night hours. Using a blend of MOS, I will forecast 
low temperatures in the mid 30s inland to the low 40s along the 


High confidence this period with dry surface high pressure 
prevailing through Thursday. Increasing moisture and some upper 
disturbances will then move through Thursday night bringing a few 
light showers. Friday should be dry before a few more showers are 
possible along a developing warm front Friday night into Saturday, 
mainly near the CSRA/Midlands. Temperatures will remain well above 
normal through the period, likely into the lower to mid 70s 
Saturday away from the coast.


Moderate forecast confidence most of the period. There is more model 
agreement now that a cold front will likely move through from the 
west Saturday night into early Sunday, with much colder high 
pressure building in thereafter through early next week. By the end 
of the period a coastal trough and a possible low pressure system 
could bring some rain back into the forecast but confidence is much 
lower toward the middle of next week. Most locales should see a half 
inch to maybe 1 inch of rain through the period, with most of the 
rain coming over the weekend. Although deep layer shear is strong we 
don't see a lot of instability so not overly concerned about the 
severe thunderstorm threat at this point and in fact we don't even 
have any mention of thunderstorms. It will also be breezy Sunday 
into early Monday and a Lake Wind Advisory may be needed for Lake 

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. Highs Monday should only range 
from around 40 near the Santee River to 50 near the Altamaha River. 
Temperatures Monday night are a bit tricky as much depends on how 
much a coastal trough and high clouds come into play but inland 
areas should get back below freezing again. Thereafter temperatures 
will modify into mid week to near or above normal levels.


Patchy fog will likely remain just north of KCHS early this 
morning. VFR conditions are expected through the 12Z TAF period. 
The TAFs will feature light west winds and clear to mostly 
clear sky.

Extended Aviation Outlook: Restrictions possible as early as Friday 
but more likely Saturday night into early Sunday, likely IFR or 
worse at times. Also, breezy/gusty conditions are expected 
later Saturday through at least Sunday night.


Today and tonight: High pressure will remain across the marine 
zones, supporting winds between 5 to 10 kts from the WNW. Seas are 
forecast to decrease by a foot today, with afternoon seas around 1 
ft across the near shore waters and 2-3 ft beyond 20 NM. Tonight, 
seas will generally remain unchanged, possibly slightly less.

Thursday through Monday: No significant concerns through Saturday 
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. Otherwise, Small Craft Advisories are likely for the entire 
area. Should see improving conditions Monday as winds turn offshore 
and diminish with the weakening cold air advection.


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 shallow saltwater flooding around
high tide. Thus, Coastal Flood Advisories will be possible.