528
FXUS62 KCHS 081724
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1224 PM EST Wed Jan 8 2025

.SYNOPSIS...
Cold high pressure will prevail into late week. A low pressure
system will impact the area Friday into Friday night, followed
by cool high pressure returning for the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
The flow aloft is quasi-zonal, while arctic high pressure moves
east through the Great Plains. Sunny skies should prevail today,
while a downslope wind component helps push temps in the upper
40s north to middle 50s south.

Tonight: A fast moving short wave will pass through the area,
allowing for a reinforcing cold front to drop southward. This
causes 850 mb temperatures to plunge as cold as minus 6 or minus
7 Celsius, with the 0C isotherm at that level to pass south of
the Altamaha River overnight. This cold advection will generate
widespread lows down in the lower and middle 20s inland, upper
20s to near 30F along the coast. Expect sub-freezing
temperatures for up to 10-14 hours tonight into Thursday
morning.

Winds never fully decouple, and with the passage of the cold
front, they actually rise a bit overnight, before the late night
inversion sinks lower to the ground closer to dawn, and winds
ease off a tad. This presents a challenge as to where any Cold
Weather Advisories will be required. The coldest temperatures
inland are where winds will be the lightest, while where winds
are more elevated closer to the coast, is where temperatures are
several degrees higher. We have good confidence on at least
parts of the region requiring a Cold Weather Advisory for
apparent temperatures in the upper teens, but there is lower
confidence on actually where. We`ll defer to later shifts to
determine where any advisory (for wind chills less of 20F or
lower) should be required.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Thursday: Quiet weather will prevail with surface high pressure in
place. Bitter temperatures will again be a concern even under full
sun. Highs will only reach the low to mid 40s across southeast South
Carolina and mid to upper 40s for southeast Georgia. Overnight
temperatures will drop into the 20s/near 30; the coldest mainly
across Berkeley, Dorchester, and Colleton counties where lower 20s
are forecast. Calm winds overnight should keep wind chills at bay,
thus minimizing the need for Cold Weather Advisories.

Friday and Friday night: A plunging shortwave diving into Central
Mexico and an embedded upper low across the Central Plains will
generate low pressure along the northwestern Gulf Coast. Meanwhile,
upper ridging will strengthen over the Southeast. The low will track
east toward the Southeastern states, with its northeastward
extending warm front lifting toward the region. Ample moisture
associated with the system will spread out well ahead and into the
western fringes of the forecast area late Friday morning and early
afternoon. Weak upper forcing and signs of initial isentropic ascent
could introduce light isolated showers across the far interior
portions of southeast SC/GA. Timing will play a large role in precip
type, but most guidance settles on solutions that show an initial
onset of liquid precip in the early afternoon. However, wet-bulbing
is one mechanism that could allow some snow to mix in from a line
near Candler County, across Screven and Colleton Counties, and
toward the Santee/Cooper Lakes. There are slightly increasing
chances for a rain/snow mixture or even all snow due to an extremely
dry thermal profile below 750 mb. Although model soundings show a
well-defined saturated warm nose around 650mb, wet-bulb temperatures
solidly below 0C down to the surface could result in enough
evaporative cooling to lower llvl temperatures enough to produce
snow in the previously mentioned areas. With morning/afternoon QPF
limited to just a couple hundredths of an inch, this would result in
trace amounts of precip/flurries. For now we maintain all rain
across the entire forecast area which still holds the greatest
chance.

As llvl flow veers easterly later in the day, we should start to see
the beginnings of WAA take shape, mainly across the coastal
locations, which should boost highs into the low to mid 50s for
those areas. Prolonged WAA across extreme southeast Georgia will
result in peak temperatures reaching near 60 degrees. On the other
hand, inland areas will only see temperatures peak in the mid to
upper 40s.

The low will then track across Georgia and toward the South Carolina
coast as widespread light to moderate showers spread in from the
west later Friday afternoon into Friday night. Warm air advection
will ramp up overnight keeping temperatures from plunging, rather
maintaining a near steady state, with lows bottoming out in the mid
to upper 30s inland and low 40s along the coast. There could be some
spots across the far interior where temperatures could dip into the
lower 30s, which maintains the concern for precip type once again.
However, probabilities are too low to include non-liquid precip for
the overnight period.

Saturday: The aforementioned low positioned across coastal North
Carolina in the morning will lift into the Mid-Atlantic. Showers
should clear the coast Saturday afternoon, leaving behind about 1/4
to 3/4 inch of total rainfall. Highs will peak in the upper 40s to
mid 50s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Dry high pressure will build back into the region from the west
Sunday and into the middle of next week. Temperatures should remain
nearly steady in the upper 40s to 50s Sunday, with warmer conditions
possible early next week.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
VFR conditions will prevail at KCHS, KJZI, and KSAV through 18Z
Thursday.

Extended Aviation Outlook: Flight restrictions likely Friday
afternoon through Saturday morning as a storm system brings
widespread rain to the area.

&&

.MARINE...
Today: Arctic high pressure will shift east through the Great
Plains, and is aligned from south of Hudson Bay in Canada to
southern Texas by sunset. The associated anticyclonic flow
around the high reaches into the immediate waters, interrupted
by a developing cold front just to our north. N and NW winds
this morning will back to the W and WNW this afternoon ahead of
the front, with speeds through the day no more than 10 or 15
kt. Seas will be just 2 or maybe 3 feet.

Tonight: The aforementioned cold front will slip through early
on, causing veering winds swinging back to the NW and
eventually the N, and brings with it considerable cold air
advection. This will allow for ample mixing of the 30 kt of 1000
mb geostrophic winds, which prompts the issuance of Small Craft
Advisories over all Atlantic waters. Winds will reach 20 or 25
kt with stronger gusts, allowing seas to build to up to 4 feet
on the nearshore waters, and as high as 5 or 6 feet further out.
Charleston Harbor winds could come close to advisory thresholds
late, but for now it is too marginal for any advisory.

Thursday through Monday: North-northwest winds will prevail through
Friday afternoon with high pressure in place. There will be a brief
reprieve of 10 kt winds and 2-4 foot seas before an area of low
pressure moves toward the area from the southwest. Conditions are
expected to reach Small Craft Advisory criteria Friday night as a
strong storm system moves through. Southwesterly winds will surge
with gusts 25-30 kt. It`s possible gale force winds could encroach
on the outer Georgia waters. Seas will peak 6-10 ft beyond 10 nm.
Conditions will improve Saturday evening in the wake of exiting low
pressure to the north and high pressure returning. Benign marine
conditions are expected through the rest of the period.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 1 AM to 10 AM EST Thursday for
     AMZ350.
     Small Craft Advisory from 10 PM this evening to 10 AM EST
     Thursday for AMZ352-354.
     Small Craft Advisory from 10 PM this evening to 1 PM EST
     Thursday for AMZ374.

&&

$$

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