Area Forecast Discussion
Issued by NWS Charleston, SC

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071
FXUS62 KCHS 281200
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
700 AM EST Tue Feb 28 2017

.SYNOPSIS...
A warm front will lift north of the area today. Atlantic high
pressure will then prevail into Wednesday, before a cold front
crosses the area Wednesday night into Thursday. High pressure will
return for the end of the week. Another cold front could impact the
area early to middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
For today: A warm front will lift north of the area this
morning, with Atlantic high pressure to fill the void left
behind, while a fast moving zonal flow will prevail aloft.
Impressive warm advection across the region, evidenced by 850 mb
temps that are near or above the 90th percentile for February
28th, will generate an abnormally warm day for our last day of
meteorological winter. We stayed very close to the 1000-850 mb
thickness, which given a thickness of 1390-1395 meters will
result in max temps 80-84F just about everywhere inland from
US-17. Keep in mind that the SC coastal locations will be
significantly cooler, with the beaches of Charleston County
likely staying in the 60s with the more direct onshore
trajectories with the sea breeze.

Westerly flow above 700 mb and the lack of forcing will be
negating factors for any convection this afternoon. But with
some CAPE and okay lapse rates, there might still be a few stray
showers/t-storms across far inland locations late in the day.
Probabilities however have been held to less than 15%, so no
mention in the gridded forecast.

Tonight: Bermuda high pressure, a synoptic set up more typical
in the warmer months, will produce another warm and humid night
across the SC Low Country and GA Coastal Empire. There is enough
mixing to prevent full decoupling within a southerly synoptic
flow, and thus lows will actually wind up near where normal
highs should be, or as much as 20F above normal.

Since there is nothing to focus on forcing for convection, a
rainfree forecast is expected.

There is likely too much wind within the planetary boundary
layer to cause any significant fog problems, but stratus build-
down and maybe sea fog, if it`s able to develop, will cause at
least patchy fog overnight.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Atlantic high pressure will prevail Wednesday ahead of an
approaching cold front. Aloft, mid level ridging will begin to be
suppressed to the south as a longwave trough shifts east from the
Midwest. The highlight of the day will be potential record-breaking
temperatures (see climate section) with highs expected to be 15-20
degrees above early March normals. Otherwise, the afternoon will get
a bit breezy with southwest winds gusting to 30 mph. A few diurnal
showers/thunderstorms will be possible in the afternoon, but the
main rain chances will come with frontal passage late Wednesday
night into early Thursday. Given the activity will enter the
forecast area overnight, when instability is typically at minimum,
it will likely be in a weakening state. However, with shear in
excess of 50 knots, a severe threat exists, albeit low. SPC
currently has most of the forecast area in a marginal risk of severe
weather. Damaging wind gusts are the primary threat within any
stronger storms.

The front should be offshore Thursday morning with precipitation
chances and cloud cover expected to quickly wane. Surface high
pressure will then build into the region from the west Thursday
afternoon into Friday. The weather post-front should be pleasant
with few clouds and seasonable temperatures.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Surface high pressure will continue to build over the area Saturday
before sliding into the Atlantic Sunday into Monday. Models are
coming into agreement that a cold front will cross the area towards
mid-week although timing is still uncertain. The only rain chances
of the period will occur with the aforementioned front. Cooler
temperatures on Saturday will be short-lived as southerly
return flow brings warmer air back into the region early next
week.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Areas of stratus and the formation of at least patchy fog will
result in MVFR or lower ceilings at KSAV and KSAV through
1400-1430Z.

Atlantic high pressure will expand across the area into tonight,
which allows for mainly VFR conditions to prevail. However,
mist/fog and/or stratus could become a concern again late in the
valid 12Z TAF cycle.

Extended Aviation Outlook: Flight restrictions possible in early
morning fog/stratus Wednesday. A cold front will move through early
Thursday with brief restrictions possible in low clouds and
showers/thunderstorms.

&&

.MARINE...
Today: Sub-tropical Atlantic high pressure will stretch across
the local waters, producing SE and South winds at or below 12
kt. Seas will average 2-4 ft, highest as one navigates further
offshore.

Tonight: The west and northwest portions of Bermuda high
pressure maintain its grip overhead. We`re embedded within a
southerly gradient that causes winds to reach as high as around
15 kt and gusty. seas will rise about a foot from today.

Wednesday through Sunday: South/southwest winds will increase
Wednesday as a cold front approaches from the west. Conditions could
approach small craft advisory criteria in the afternoon into early
Thursday, mainly in the outer portions of AMZ350 & AMZ374 and
possibly in the Charleston Harbor. Will continue to assess trends.
The front is expected to cross the waters early Thursday, with
winds/seas to improve thereafter. High pressure will then prevail
late week into the weekend. No headlines are expected, although a
brief wind surge will occur Saturday morning as cold advection
ensues.

Sea Fog: Models are insisting that sea fog should already be
ongoing, but also that sea fog will continue through tonight
and beyond. However, trajectories are still not parallel enough
to the coast line today, and once they become so tonight, wind
speeds look a little too strong. For now e prefer to show
nothing more than patchy fog later tonight, but with the caveat
that with such a warm and humid air mass, sea fog could develop
almost instantly at any time.

If and when it does form, it could last until a cold front
sweeps over the region Wednesday night.

&&

.CLIMATE...
Record high temperatures for March 1:
CHS: 82 degrees last set in 1997
CXM: 79 degrees set in 1918
SAV: 86 degrees set in 1918

Record high minimum temperatures for March 1:
CHS: 61 degrees set in 2012
CXM: 63 degrees set in 2012
SAV: 65 degrees last set in 2012

Record Mean Average Temperature for December through February
KCHS:
1. 1948-49...57.0 degrees
2. 2016-17...56.8 degrees (through February 27)
3. 1949-50...56.1 degrees

Record Mean Average Temperature for December through February
KSAV:
1. 1931-32...61.7 degrees
2. 1889-90...60.2 degrees
3. 1948-49...59.0 degrees
4. 1879-80...58.9 degrees
5. 2016-17...58.5 degrees

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
CLIMATE...



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