Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 201134
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
634 AM EST Mon Nov 20 2017

.SYNOPSIS...
High pressure will prevail into Tuesday. Low pressure will pass
off the Southeast coast Tuesday and Tuesday night, followed by
additional low pressure systems Thursday into Friday. A cold
front will shift through the area Saturday night or Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Westerly flow aloft this morning will gradually back to
more southwesterly as a mid/upper level trough digs across Texas
and the northwest Gulf of Mexico coast. At the surface, high
pressure positioned to the north will slip eastward and become
aligned along the coast of the Carolinas. Today will be very
quiet with clear skies prevailing into the afternoon before
scattered high clouds begin to stream in from the southwest in
response to the developing trough aloft. The position of the
surface high will help drive a cool northeast flow for most of
the day, and temperatures are expected to range 6-8 degrees
below normal. Forecast highs are in the low 60s in most areas
with some mid 60s possible in southeast Georgia.

Tonight: The center of the surface high will move offshore,
though it will continue to extend into Georgia and the Carolinas
through the overnight. High clouds will steadily increase as
will stratocumulus in response to subtle isentropic ascent. A
coastal trough will begin to take shape just offshore late in
the overnight, and there could be enough convergence to squeeze
out a light shower over the coastal waters. However, the model
consensus favors a dry forecast through sunrise Tuesday. With
increased cloud cover expected, radiational cooling conditions
will not be as favorable and forecast lows mainly range from the
low 40s inland to the upper 40s/low 50s at the coast.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
The surface high will gradually retreat to the east on Tuesday
while a longwave upper trough deepens over the eastern half of
the country. A weak surface low is expected to develop over
northern FL and shift up the coast late Tuesday into Tuesday
night. Light showers are expected to develop across coastal
southeast GA by Tuesday afternoon, spreading into southern SC
late in the afternoon or during the evening. The rain should
then taper off from southwest to northeast late Tuesday night or
Wednesday morning as surface high pressure builds from the
west.

Another strong shortwave will move through the Deep South
Wednesday into Thursday, resulting in another surface low moving
up the coast. In this case, dry high pressure will remain
inland, potentially limiting the inland extent and intensity of
the associated rain. We are showing the greatest PoPs along the
coast with only 20-30% farther inland. With the cool high
pressure in place and extensive cloud cover on Thursday, highs
will only reach the upper 50s to lower 60s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Some model differences remain regarding how long the coastal
low will linger into Friday and thus the precipitation
potential. We hung onto slight chance PoPs through Friday
despite some guidance showing morning drying. For the rest of
the weekend, a dry cold front will swing through Saturday night,
but high pressure will generally prevail.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
VFR conditions will prevail at KCHS and KSAV through 12z
Tuesday.

Extended Aviation Outlook: MVFR/IFR ceiling/vsby likely Tue
night into Wed morning at both terminals due to low clouds and
rain. MVFR conditions possible Thursday night into Friday
morning as another low pressure system moves up the coast.

&&

.MARINE...
Through tonight: High pressure will remain to the north of the
local waters and will help to keep an enhanced pressure gradient
in place. This will support 15-20 knots across most of the
waters through this morning, before a slight decrease to around
15 knots by late today. Then overnight, the high will slide
offshore and a coastal trough will begin to set up. In response,
winds will turn more easterly and south-southeasterly with time
with speeds around 15 knots. Seas will generally average 2-4
feet across the area.

Northeast winds will be the rule during mid to late week as
high pressure builds from the northwest and a series of low
pressure systems move up the coast. The strongest gradient is
anticipated late Wednesday night through Thursday night during
which Small Craft Advisories are likely.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Frost Advisory until 9 AM EST this morning for GAZ087-088-
     099>101-114-115.
SC...Frost Advisory until 9 AM EST this morning for SCZ040-042>045.
MARINE...None.

&&

$$

NEAR TERM...BSH
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...BSH/JRL
MARINE...BSH/JRL


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