Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 222336
Area Forecast Discussion
National Weather Service Charleston SC
736 PM EDT Wed Mar 22 2017
High pressure will build in from the north through Thursday night
before shifting into the Atlantic on Friday and persisting through
the weekend. A cold front could affect the area early next week.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
An omega block is developing aloft across the nation, featuring
ridging in the central states, anchored on both sides by large
scale troughing. We`re situated in the region of a northwest
flow between an Atlantic trough and ridging just to the west. At
the surface, a huge 1036 mb high over the Great Lakes shift
southeast and settle into the Alleghenies late tonight, with an
associated wedge to punch it`s way south and southwest through
the Carolina`s and into Georgia. The resulting subsidence
within this pattern and PWat`s that are below normal will
support a rainfree night everywhere within the CWFA. Although
there will be varying amounts of mid and high level clouds
throughout, these will fade with time overnight, perhaps
replaced by some marine-induced stratocumulus over coastal
Georgia after midnight. There is enough CAA to support lows some
10-15F cooler than this morning, with maybe a few places in
northern Berkeley County sneaking into the upper 30s, while
McIntosh County will be the warmest with lows in the mid 50s due
to more cloud cover and some onshore fetch.
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Thursday and Friday: A wedge of high pressure will be fully
entrenched over the region Thursday, bringing dry and cooler
conditions within a persistent northeast flow. In general, afternoon
highs will peak in the low/mid 60s. Thursday night lows will range
in the mid/upper 40s away from the coast. A high amplitude ridge of
high pressure aloft will then extend across the Southeast on Friday
while the wedge begins to weaken at the sfc. The pattern will lead
to noticeably warmer conditions than the previous day. In general,
highs will range in the low/mid 70s Friday afternoon. Dry conditions
will persist into Friday night with low temps ranging between the
Saturday: The area will be positioned between a mid/upper lvl ridge
of high pressure extending across the Southeast coast and a deep low
pressure system advancing over the Central United States. The
pattern will result in a strong return flow from the Atlantic well
ahead of the low pressure system to the west. The combination of
increasing lvls of moisture and isentropic lift will help produce
clouds over the area, but showers should hold off over the region
until at least Saturday night. Temps will be warmer than the
previous day, ranging in the mid/upper 70s over most areas away from
the immediate coast.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
A mid level short wave and the associated sfc low are forecast to
ripple across the region early next week. Forecast sounding indicate
that diurnal weak CAPE will likely develop each afternoon Sunday
through Tuesday. A sfc cold front should sweep across the region
late Tuesday. The leading edge of a Canadian air mass should spread
across the CWA on Wednesday. Temperatures appear above normals,
generally in the upper 70s to low 80s. I will mention at least SCHC
PoPs for shra/tsra each afternoon and evening Sunday through
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
VFR, with NE-E winds averaging 10-20 kt through sunset Thursday
Extended Aviation Outlook: VFR conditions will prevail through
Friday. Brief flight restrictions possible Saturday into Sunday
with low clouds and showers/thunderstorms.
Tonight: An expansive anticyclone covering most of the country
east of the Mississippi and extending into the western Atlantic,
will dominate the synoptic pattern. Constant pressure rises
averaging around 1 mb every hour and a tightening of the
clockwise gradient, will produce Fresh to Strong NE-E breezes
over the ocean, and a solid 15-20 kt in Charleston Harbor.
Soundings suggest a chance for gale force force gusts during the
late evening and overnight, but with geostrophic winds of 35-40
kt, this suggests that any risk would be marginal, thus no Gale
Warning is necessary. Charleston Harbor still might require an
advisory and we continue to carefully monitor trends. The
favorable onshore fetch will allow for building seas, reaching
as high as 6 or 7 ft within 20 nm, 8 o 9 ft further offshore,
while waves in Charleston Harbor will be at least 1-2 ft.
Strong cold air advection associated with high pressure will produce
strong northeast flow over all coastal waters Wednesday into
Thursday. Small Craft Advisories will therefore remain in effect for
all waters outside the CHS Harbor through much of Thursday until the
pressure gradient weakens as sfc high pressure shifts offshore. In
general, winds should peak between 25-30 kt early Thursday while
seas peak between 5-7 ft nearshore and 7-9 ft in offshore Georgia
waters. Conditions will likely improve to below Small Craft Advisory
levels for nearshore waters Thursday night, while higher seas linger
in offshore Georgia waters into Friday. Steady south to southwest
winds are forecast to remain over the zones through the weekend.
Rip Currents: A strong northeast wind and a 6-7 second northeast
swell will develop/occur as high pressure builds over the waters
into Thursday. A moderate risk of rip currents is therefore in
effect for all beaches along the Southeast South Carolina and
Southeast Georgia coast Thursday.
MARINE...Small Craft Advisory until midnight EDT Thursday night for
Small Craft Advisory until 6 PM EDT Friday for AMZ374.
Small Craft Advisory until 6 PM EDT Thursday for AMZ350.