Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 231946
Area Forecast Discussion
National Weather Service Charleston SC
346 PM EDT Sun Oct 23 2016
High pressure will prevail into Monday. A dry cold front will move
through Monday Night and be followed by strong high pressure into
the middle of the week. A weakening cold front will approach late in
the week, before high pressure returns for next Saturday.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
High pressure will be centered to the west while a lee-side trough
sets up east of the Appalachians as weak low pressure moves off
the southern New England coast. Clear skies, a dry atmosphere and
very little wind will allow for great radiational cooling to start
the night before boundary layer winds increase a tad given the
tightening pressure gradient, mainly across SC. This could affect
low temperatures a bit but for now we stayed on the cooler side of
the model guidance with lows in the lower to mid 40s inland and
mid- upper 50s at the coast.
.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Monday: The mid and upper trough will prevail over the east coast
and western Atlantic with a deep W-NW flow to maintain a continued
of nothing but dry air with PWat at best 1/2 to 3/4". An east-west
ridge of surface high pressure from Texas along the northern Gulf
coast states with stretch into the SW Atlantic. This feature will
drift south in advance of a dry cold front that approaches our CWFA
from the north by evening. Warm advection, plenty of sunshine (aside
from some cirrus clouds) and compressional heating in advance of the
front will result in a gigantic swing of temps, as much as 35-40F in
some areas. Expect max temps in the upper 70s-lower 80s, except
lower-middle 70s along the coastal sections from Tybee Island to
Monday Night: The cold front drops south through the area void of
any sensible weather, absent any moisture and short wave energy.
Approximate timing of the frontal passage is through the Charleston
quad-county area by midnight, crossing the Savannah River around 2-3
am and pushing south of the Altamaha River around or shortly after
daybreak Tuesday. There is several hours of radiational cooling in
advance of the front, especially over or central and southern
counties, before modest cold advection lags a little behind the
front as stronger high pressure builds behind the front from the
Midwest and western Great Lakes. Lows won`t be anywhere near as
cool as the past couple of nights.
Tuesday through Wednesday: The mean long wave trough off the mid-
Atlantic and southeast coast Tuesday gives way to short wave ridging
Wednesday, while high pressure covers much of the eastern half of
the nation Tuesday and much of the eastern third on Wednesday. It`ll
be another dry day on Tuesday with the lack of moisture and large
scale subsidence. But there are indications that maybe a few showers
could sneak onshore of coastal Georgia by late Wednesday as the
synoptic flow turns more easterly in sync with better low level
convergence and isentropic lift. Moisture is still limited however
so for now we`re just showing an increase in marine induced
stratocumulus. Modest pinching of the gradient both days will allow
for breezy conditions at and near the coast, as high as 25-30 mph
Tuesday, 20-25 mph Wednesday. As is common this time of year within
the dry air mass, look for a large diurnal fluctuation in
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Models have come into better agreement in the long term. Broad high
pressure will shift offshore Thursday while an upper level trough
and associated surface low pressure move across the Great Lakes. A
cold front should stretch down into TN Valley, but it`s expected to
weaken as it approaches our area. The front is forecasted to pass
just north of our area Thursday night into Friday. There is not much
moisture with this front and the model trend has been drier. We
lowered POPs across the area, limiting the slight chance POPs to the
Charleston Tri-County area. But this may still be overdone given the
trend. High pressure builds across the Southeast on Saturday.
Temperatures may be a few degrees above normal in the long term.
.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Extended Aviation Outlook: VFR.
Tonight: High pressure will prevail centered inland across the
Southeast U.S. with mainly light offshore winds across the
southern SC/northern GA coastal waters. The strongest winds near
10 kt will be across the Charleston County waters where the
pressure gradient will be a bit greater. Seas will generally
subside slowly...averaging 1-2 ft within 20 nm and 2-3 ft in the
GA offshore waters.
Monday and Monday Night: High pressure will hold on one more day,
before giving way to an east-west oriented cold front at night.
Westerly flow at or below 10-12 kt will back to the SW in advance of
the front due to resultant sea breeze influences, before they veer
around to the NW and N at less than 15 kt in wake of the front
during the night. Expected timing of the front moving through is
around midnight-2 am over the South Carolina waters, moving south
through the Georgia waters thereafter, reaching south of the marine
area around 7-8 am Tuesday. Seas are limited to about 2 ft through
much of the period, building a foot or two toward daybreak Tuesday.
Tuesday through Wednesday: A strong Canadian High will build in wake
of the cold front through the mid week period. Some combination of a
tightened gradient, occasional cold advection and/or isallobaric
pressure rises will cause Fresh to perhaps periodic Strong NE-E
breezes (WMO Force 5 or 6 on the Beaufort Wind Scale), and Small
Craft Advisories could be required for at least parts of the
Thursday through Friday: High pressure along the eastern seaboard at
the start of the period is forced east and southeast by Friday in
advance of low pressure moving from the Ohio Valley into the NE
states, with a trailing cold front that weakens by the time it gets
into closer proximity to the local area. Winds and seas are forecast
to remain below any Small Craft Advisory levels.