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Area forecast discussion 
National Weather Service Charleston SC
152 am EDT Sat Nov 1 2014

Synopsis...
a strong cold front will move through late tonight...followed by
unseasonably cold high pressure into early next week. The high will
eventually shift offshore during the middle of next week as another
cold front approaches from the northwest.

&&

Near term /until 6 am this morning/...
what a potent system so far...and it will only get stronger
overnight and Saturday.

The pre-frontal trough and associated convection has pivoted north of
the Santee river and there will be a break until late tonight when
some additional showers move in along the northwest tier of SC once the
deep layered low aloft heads our way.

Meanwhile...the Arctic cold front will sweep through most of
southeast Georgia and inland southeast South Carolina...before
slowing as it nears the Charleston tri-County area as a wave of
low pressure forms over the Pee Dee. Cold air is quite impressive
and as it starts to surge in it will break the nocturnal inversion
and with packing of the gradient it will result in occasional
gusty west/northwest winds...as high as 15-25 miles per hour across southeast Georgia and 10-20
miles per hour in SC.

Temperatures at midnight will be likely be greater than what temperatures will
be during the day Saturday...and by morning with a continued
influx of cooler Canadian air we/ll see lows down near 40 from
Hampton and Allendale to Tattnall...lower and middle 40s most
elsewhere...except for a few upper 40s over coastal Charleston.
This will be some 6-10 degrees below typical November 1 levels.

&&

Short term /6 am this morning through Monday/...
Saturday...significant changes are in the offing for the area as an
incredibly cold and powerful system for early fall affects the
eastern U.S. This weekend. Models are similar in showing a potent
shortwave digging south across the middle Mississippi Valley tonight
and briefly cutting off across South Carolina on Saturday as a
strong 115 knots jet streak rounds the base of the mean trough axis. An
Arctic cold front will be driven quickly south via strong cold air
advected noted in the wake of the shortwave...which will quickly
encompass the southeast states over the weekend...bring extremely
chilly conditions to the region for early November. By Saturday
afternoon when the upper low is overhead...500 hpa temperatures are
forecast to drop in the -22 to -26c range with 850 hpa temperatures
falling to -2 to -5c. It should be noted 850 hpa temperatures of
this magnitude for early November are about 12 Standard deviations
below normal--certainly a testament to how cold this air mass will be.

Temperatures: considerable cloud cover within the associated upper
low/S cold pocket coupled with such cold low/mid-level thermal
profiles will support highs only in the upper 40s across the north
to the middle 50s across the south. If some model data sets prove to be
correct...such as the NAM-12...and/or precipitation is much more
widespread than expected...the resulting diabatic cooling could keep
temperatures in the 40s for all but the far south where lower 50s
could be realized. Its certainly a tough call on high temperatures
with the eventual diurnal thermal curves being driven by the
area/intensity of any precipitation that develops. If the current
forecast holds...the record low maximum temperature of 56 /1993/ at
the Charleston Airport could fall. See the climate section below for
additional information. Lows Saturday night will range from the middle
30s across the southwest areas to the upper 30s/near 40 elsewhere.
The atmosphere looks a bit too dry and the wind too high to support
anything more than patchy frost across the far interior southeast
Georgia...roughly from Millen south to Tattnall and points west. A
frost advisory is not anticipated at this time.

Precipitation: models are similar in depicting various amount of quantitative precipitation forecast
across mainly southeast South Carolina Saturday afternoon as upward vertical velocity
ahead of the upper low spreads across the area. Most of the guidance
keeps the bulk of the precipitation to the north across the midlands
and Pee Dee regions...only giving southeast South Carolina a
quick...glancing blow. Will limit probability of precipitation to 20-40 percent across the
central and northern parts of the forecast area for now...highest
across the far north...roughly north of I-26...but any slight
southward deviation of the upper low will necessitate a higher pop
regime. There may be just enough diabatic cooling to support some
graupel/small hail at times...mainly in pockets of heavier rain
where diabatic processes will be maximized. Could also hear a
rumble or two of thunder across the north given the incredible low
lapse rates...but the risk is just too low to mention just yet.

Winds...breezy to windy conditions are likely Saturday with strong
cold air advection expected. The windiest conditions will be found
south of I-16 where mixing will be maximized due to considerably
less cloud cover. Expect winds of 20-30 miles per hour with gusts to 40-45 miles per hour
in this area...so a Wind Advisory will be issued for Tattnall-Evans-
Bryan-Chatham-Liberty-long and McIntosh counties...from 9am-8pm
Saturday. There is a possibility winds could reach advisory levels
for the South Carolina coastal counties...but the presence of
extensive cloud cover lowers confidence enough to not issue a Wind
Advisory for those locations with this forecast cycle. Plan to limit
winds there to 20-25 miles per hour with gusts 35 miles per hour...or just below Wind
Advisory thresholds.

Sunday...temperatures will begin to moderate some as cold air
advection wanes and the center of the Arctic high settles directly
overhead. Highs look to warm into the middle-upper 50s under mostly
sunny skies. It will be down right cold Sunday night with lows
ranging from the lower 30s to the middle-upper 30s at the coast with
Lower-Middle 40s at the beaches. There will be a risk for frost/freeze
conditions with scattered to widespread frost likely roughly north
of a Huger-Summerville-Hendersonville-Clyo-Metter line...but away
from the shores of Lake Moultrie. A frost advisory will likely be
needed for these areas. Lows around freezing are possible across
parts of Jenkins-Screven-Allendale as well as northern parts of
Berkeley County...but expect any freeze durations to remain 1-2
hours at best. A freeze watch and eventually a warning may be needed
in later forecast cycles.

Monday...warmer conditions Monday with highs in the upper 60s with
lows in the lower 40s inland with middle-upper 40s at the coast. Dry
conditions will prevail.

Lake winds...winds will be strong and gusty Saturday into early
Sunday behind a strong cold front moving through early Saturday.
Strong cold air advection over the warmer lake waters will make for
very unstable conditions which will allow strong low-level winds to
mix down to the surface...likely around 35 knots at times...possibly
close to 40 knots. A lake Wind Advisory remains in effect.

&&

Long term /Monday night through Friday/...
high pressure looks to slide offshore through middle week with
moderating temperatures getting back above normal Tuesday. A cold
front looks to approach later in the week...possibly moving through
Thursday night. Limited moisture with the front means little to no
rain chances however.

&&

Aviation /06z Saturday through Wednesday/...
kchs...the cold front will swing through around daybreak and as
colder air starts to rush in and deeper mixing occurs...W/NW winds
will become stronger and progressively more gusty through the
morning. Wind gusts will peak around 30 knots in the afternoon. In
addition...steep lapse rates and plenty of low level moisture will
cause scattered to numerous rain showers to occur through the day
Saturday...and have prevailing rain showers in the forecast from 16-23z.
Some graupel/small hail could occur as well but confidence not
high enough to have mention in the taf/S. While some flight
restrictions are possible...especially with the precipitation in
the afternoon...have kept VFR conditions prevailing in the taf/S.

Ksav...the cold front will swing through prior to daybreak and as
colder air starts to rush in and deeper mixing occurs...W/NW winds
will become stronger and progressively more gusty through the
morning. Wind gusts will peak around 35 knots in the afternoon. The
best chance of rain showers looks to stay north of the terminal
Saturday...unless wrap-around moisture is further south than now
anticipated. VFR conditions are forecast to prevail through 06z Sunday.

Extended aviation outlook...no impacts expected sun-Wed.

&&

Marine...
overnight...mariners can anticipate a ramping up of winds and
seas as a strong Arctic cold front moves into and through the
local waters. Cold advection will begin in ernest in wake of the
front that along with a tight pressure gradient in response to
the pressure difference between Canadian high pressure dropping
into the central U.S. And low pressure starting to form near the
SC/NC line will cause a sharp rise in winds. We/ll be close to
gales by late tonight across amz354-374...thus have initialized
with the Gale Warning on these waters. Conditions on the SC
waters should hold near or just below any headline criteria until
closer to daybreak Saturday...when we have gales starting on
amz330-350-352. Seas will be restricted some by the offshore fetch
but will still build from around 2-4 feet early upwards to 4-7 feet by
late...highest across the outer Georgia waters.

Saturday...dangerous conditions are expected over all waters
Saturday with the potential for solid gales increasing. Gale
warnings will be issued for all marine zones...including the
Charleston Harbor. Expect winds of 30-35 knots with gusts to 40 knots
nearshore waters and 35-40 knots with gusts to 45 knots offshore waters.
Seas will range from 4-7 feet nearshore...8-13 feet offshore. 1000 hpa
geostrophic winds are forecast to be 50-60 knots...so its entirely
possible a few gusts to storm force />=48 knots/ could occur...
especially over the warmer offshore waters. Although not likely
at this time...a Storm Warning may eventually be needed for some
legs...especially Saturday afternoon when winds are forecast to peak.

Saturday night through Wednesday...improving conditions expected
later Saturday night into Sunday with winds dropping below advisory
levels by early afternoon...although seas will take a bit longer to
do so beyond 20 nm. No issues from Sunday night through Wednesday although
seas will be building back up later in the period given the
persistent east winds on the south side of high pressure.

Blowout tides...strong offshore winds are likely to push tides into
the -1 to 0 feet MLLW Saturday into Sunday. At this time it does not appear as
through levels will reach levels where navigation problems
occur...but this will watched carefully.

&&

Fire weather...
very breezy to windy conditions expected Saturday behind a strong
cold front. Winds could gust near 40-45 miles per hour...especially over
southeast Georgia. This is where fuel moistures appear to be lowest
given the lack of recent rainfall. At this time minimum relative
humidities are not expected to reach critical thresholds
/25 percent/...but this could change if the air mass is a bit warmer
and/or drier than currently expected. Conditions could be a bit
drier Sunday although winds will be much lower. In any
event...land managers are encouraged to pay attention to the latest
forecasts this weekend. Headlines for critical winds and near
critical relative humidity will be added to the fire weather planning forecast.

&&

Climate...
record low maximum temperatures for Sat Nov 1...
kchs 56 /1993/...
ksav 52 /1925/...
kcxm 52 /1925/...

&&

Chs watches/warnings/advisories...
Georgia...Wind Advisory from 9 am this morning to 8 PM EDT this evening
for gaz114>119-137>141.
SC...lake Wind Advisory from 6 am EDT this morning to 11 am EST
Sunday for scz045.
Marine...Gale Warning from 6 am EDT this morning to 4 am EST Sunday for
amz330-350-352.
Gale Warning until 5 am EST Sunday for amz354-374.

&&

$$

Near term...
short term...St
long term...rjb
aviation...jaq
marine...
fire weather...
climate...

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