St. Andrews, South Carolina 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

256
FXUS62 KCAE 031126
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
626 AM EST Tue Dec 3 2024

.SYNOPSIS...
An arctic air mass will settle over the area today with below
normal temperatures likely into Wednesday. Guidance has been
consistent supporting low temperatures in the upper teens to
lower 20s tonight. Thursday will be breezy with near normal
temperatures before a dry cold front moves through and
temperatures fall again. Forecast confidence decreases late this
weekend and into early next week when a pattern change may
bring a period of unsettled weather to the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Message(s):

- Unusually cold temperatures expected.

The longwave trough in the eastern CONUS will be moving off the
coast this afternoon with northwest flow aloft across the
region. The strong mid level short wave trough evident on water
vapor imagery is moving east across north central North
Carolina. Stronger lift and moisture staying mainly northeast
of the Midlands. Band of snow showers on radar moving east-
southeast into the North Carolina Coastal Plain. Perhaps a few
flurries in the north Midlands before dawn but becoming less
likely as moisture is limited below 800 mb and the lift is
shifting east. Arctic front has moved into the southeast
Midlands and will be south of the area by daybreak. The modified
arctic air mass was located over the Plains at 08z. This ridge
of high pressure will be building southeast toward the
Southeastern U.S. today and will settle over the area tonight.
Strong cold advection through the day and temperatures will
struggle to rise into the low to mid 40s. Some clouds through
the morning with another short wave trough approaching, but
mostly sunny by the afternoon. Winds may be a tad gusty through
mid morning as the pressure gradient tightens a bit, but as the
ridge builds in this afternoon winds will diminish. Unusually
cold temps expected tonight for this time of year. There is
warm advection developing in the low-levels overnight, but with
the 1032mb surface ridge axis across the area by morning, clear
skies, boundary layer decoupled and dry air, expect strong
radiational cooling conditions. Forecast low temps below the
Mos and near the NBM median temps. The NBM low temp
probabilities < 20 degrees remain high especially across the
Piedmont and outlying areas. So continued overnight lows in the
upper teens to low 20s.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Key Message(s):

- Below normal temperatures continue on Wednesday.

- Warmer and breezy Wednesday Night and Thursday as a cold
  front moves through.

- Chilly temperatures return Thursday Night.

The upper flow becomes westerly on Wednesday in advance of a
deepening trough over the Great Lakes. The trough axis passes
to our north Wednesday Night, with troughing lingering over the
eastern CONUS for the remainder of the short term. At the
surface, high pressure will be overhead at the start of the
forecast period, being forced south into Florida ahead of an
approaching cold front. Another strong area of high pressure
builds in behind the boundary for Thursday Night.

Wednesday and Wednesday Night: After a chilly start to the day,
temperatures are able to reach the upper 40s to lower 50s.
While warmer than previous days, these values are about 10
degrees below normal. Clouds increase later in the day ahead of
an approaching cold front. The pressure gradient also tightens
ahead of the boundary with winds speeds increasing, especially
towards daybreak. Maintaining a dry forecast with the passage of
the cold front as probabilities are generally low, 10 to 20
percent, across the FA with the highest values in McDuffie
County. Due to the clouds and mixing within the boundary layer,
overnight temperatures will be noticeably warmer with values in
the mid to upper 30s. While breezy conditions are expected,
probabilities of Lake Wind Advisory criteria being met remain
low.

Thursday and Thursday Night: The day begins with breezy
southwesterly flow. The winds shift westerly and then
northwesterly while decreasing as the day goes on and the cold
front clears the FA. Skies will clear out from north to south
behind the boundary. Guidance is in good agreement that
temperatures will be near seasonal values during the daytime
hours with highs in the mid to upper 50s north and west of I-20
and the upper 50s to lower 60s elsewhere. Clear skies, CAA, and
diminishing winds at night should be favorable for radiational
cooling, though there is uncertainty regarding how quickly the
winds die off. Leaned towards the deterministic for now as the
blend seems too low given these parameters. It will be a chilly
night even in this scenario with forecast lows in the upper
teens to mid-20s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Key Message(s):

- Uncertainty increases late this weekend and into early next
  week when a pattern change may bring a period of unsettled
  weather to the region.

The extended period begins with a split flow followed by the
passage of weak upper ridging this weekend ahead of a possible
storm system for Monday. Meanwhile, strong high pressure in the
Midwest at the start of the period passes to our north Friday
Night with temperatures and moisture increasing behind it this
weekend. Friday begins cold and dry with below normal
temperatures followed by another chilly night due to favorable
radiational cooling conditions. A gradual warming trend is then
expected for the weekend and Monday. The forecast uncertainty
increases late Sunday and into early next week as the
deterministic GFS and Euro remain highly divergent in the
evolution of the Synoptic pattern and rain chances. The GFS
brings a warm front through the FA Sunday Night followed by
several days of unsettled weather. The Euro by contrast keeps
the region generally dry. Given the high level of uncertainty,
PoPs were capped in the Chance category and the NBM was showing
moderate to high probabilities of precipitation towards the end
of the current forecast period.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
VFR conditions continue through the TAF period.

A few strato-cumulus/Alto cumulus this morning mainly north of
the terminals as mid level trough moves northeast of the area.
High pressure is building into the region from the northwest as
a cold front has pushed southeast of the area. Winds mainly
north to northwest near 10 knots. Winds may be gusty through
mid morning then the pressure gradient will relax a bit. Dry
high pressure across the region overnight and expect clear sky
and near calm winds.

EXTENDED AVIATION OUTLOOK...Low-level wind shear possible
Wednesday night ahead of a cold front. Otherwise, no significant
impacts to aviation expected.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...None.
GA...None.

&&

$$

SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...