Area Forecast Discussion
Issued by NWS Charleston, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS62 KCHS 231255

Area Forecast Discussion
National Weather Service Charleston SC
755 AM EST Thu Nov 23 2017

A series of low pressure systems will move up the coast today
through Friday. A cold front will shift through the area
Saturday night, followed by dry high pressure through the
middle of next week.


As of 750 AM: I will issue a quick update to increase PoPs to
chc to schc across the coastal counties.

As of 635 AM: Composite radar images indicate that light
rainfall was spreading north across SE GA and the lower Savannah
River Valley. Observations indicated that the low values of dBZ
were associated with very light rain to sprinkles. I will update
the forecast to adjust PoPs slightly higher and inland. In
addition, I will increase sky and tweak hourly temperatures to
align with observations.

As of 340 AM: Regional radar composite indicated low values of
dBZ spreading north across SE GA. The activity was developing
north of sfc low pressure developing near the Big Bend of
Florida early this morning. Recent surface observations
indicated that drizzle to light rain was occurring under the
radar returns. I will indicate schc to chc values of PoP
gradually increasing across SE GA early this morning, then
increasing across SE SC after sunrise. The axis of a mid level
trough is forecast to slide east through the day, reaching the
SC/GA coast late this evening. As the trough pushes east, low
pressure is expected to track northeast off the Southeast coast.
It appears that a compact rain shield will exist northwest of
the low center as high pressure remains centered over the
DelMarVa. In fact, near term guidance indicates that the
H850-700 frontogenesis will track over the adjacent Atlantic
waters. Given the passage of the deeper forcing and instability,
the greatest rainfall rates will remain off shore today. It
appears that rainfall totals from today through tonight will
peak around a quarter of an inch across the coastal counties,
further inland will struggle to see measurable rainfall. Steady
NE winds and thick cloud cover should limit high temperatures in
the upper 50s.

Tonight: Low pressure will slowly track northeast, leaving at least
partly cloudy conditions across the CWA through the night. Steady NE
winds should strengthen slightly late tonight as the pressure
gradient increases in the wake of the low. However, the GFS and NAM
indicate very weak H85 CAA late tonight, generally cooling around a
degree during the pre-dawn hours. A few weak showers will likely
linger near the coast for most of the night, but conditions should
become dry toward dawn Friday. Using a blend of MOS, low
temperatures should range from the low 40s inland to around 50
across the beaches.


The latest model suite is in better agreement on a less
amplified upper shortwave moving through on Friday which
translates to a slightly weaker and farther east coastal low
track. We held onto slight chance showers along the immediate
coast Friday with greater coverage over the waters, though even
this might be a tad overdone if the 00Z GFS verifies. Cold
advection will yield highs in the low to mid 60s.

Dry weather is anticipated Saturday through Sunday. A broad
upper trough pattern will persist, with weak surface high
pressure moving east of the area on Saturday, allowing a
southwest flow to bring warmer temperatures in the upper 60s. A
potent northern stream shortwave will drop through the area
Saturday night, pushing a dry cold front past the area.
Expansive dry high pressure will spread over the southeast
United States on Sunday, dropping high temps a few degrees.


Dry high pressure will prevail Sunday night through Wednesday. A
cold front may approach late Wednesday or on Thursday,
potentially bringing scattered showers to the area. Sunday and
Monday will be slightly cooler due to the influence of cold high
pressure. Temps warm up during mid week as the high shifts east
and southerly flow develops.


Periods of light rain will pass over the terminals today into
this evening, the greatest rates should occur between 20-24Z.
Cloud bases should lower from around 10 kft around TAF onset to
around 3.5 kft by midday. MVFR ceilings should accompany the
heavier rainfall rates late this afternoon and early evening. In
addition, the center of sfc low pressure is forecast to pass off
the GA/SC coast between 21-03Z. Tonight, VFR conditions with
steady NE winds is expected at KCHS and KSAV.

Extended Aviation Outlook: MVFR ceilings could continue into
Friday at both terminals, then VFR returns.


Sfc low pressure is expected to develop near the Big Bend of Florida
early this morning, as high pressure remains centered over the
DelMarVa region. The high is expected to move very little through
tonight. The sfc low is forecast to track NE off the GA and SC coast
today into tonight. This pattern will support gusty NE winds across
the marine zones today and tonight. Wave guidance indicates that
wave heights will increase through this morning, with 6 foot seas
spreading into the nearshore zones this afternoon. Winds are
forecast to increase this evening and tonight, with gusts around 25
kts common. A Small Craft Advisory will be in effect outside the CHS
Harbor afternoon noon for the nearshore waters, outer GA waters will
remain in effect through the period.

Marginal Small Craft conditions will extend into Friday over the
nearshore waters and into Friday night for the offshore GA
waters, mainly due to some residual 6 ft seas. Then, sub-
advisory conditions will prevail through at least the middle of
next week as high pressure takes hold.


MARINE...Small Craft Advisory from noon today to noon EST Friday for
     Small Craft Advisory until 3 AM EST Saturday for AMZ374.


MARINE...JRL/NED is the U.S. government's official web portal to all federal, state and local government web resources and services.