National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 170822
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
422 AM EDT Fri Aug 17 2018

.SYNOPSIS...
The area will stay between an inland trough and high pressure in
the Atlantic through early next week. A front will approach the
area from the west towards the middle of next week.

&&

.NEAR TERM /THROUGH TODAY/...
The synoptic pattern will change little today with the region
aligned along the western flanks of subtropical high pressure.
Convection will once again be clustered near and inland of the
afternoon resultant sea breeze circulation. Similar to
yesterday, the strongest sea breeze convergence looks to setup
along the Georgia coast where both the RAP and H3R show the
greatest concentration of convection by early-mid afternoon.
Activity will gradually develop inland mid-late afternoon as
convection along the immediate sea breeze weakens/dissipates and
additional convective outflows emerge. Closer to sunset,
activity along the northward moving Gulf Coast sea breeze will
make a run for the Altamaha River. There are signals in a few of
the CAMs that some of this convection will push north of the
river and impact much of interior Southeast Georgia, but
confidence how this scenario will evolve is only moderate at
best this far out. Will carry 20-50% pops this afternoon
through sunset with highest average pops clustered along the
Georgia coast and areas roughly along/south of the I-16
corridor, including the Savannah Metro Area. Highs will warm
into the lower 90s under partly to mostly cloudy skies.

Modified soundings yield little in the way of meaningful DCAPE
with values averaging 500-700 J/kg so the risk for damaging, wet
microbursts is low. PWATS will approach 2.25 inches later today
which will support a locally heavy rainfall with a potential
for minor flooding, mainly in low-lying and poor drainage areas.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
Tonight: Convection, mainly over interior Southeast Georgia,
will gradually diminish through midnight. The risk for isolated
showers/tstms will shift back into the Atlantic during the early
morning hours Saturday. Extensive debris cloudiness will be
slow to thin with mostly cloudy skies likely to hold for much
of the night. Lows will range from the lower 70s inland to upper
70s/near 80 at the beaches.

Saturday: In the morning the mid-levels will consist of broad high
pressure to our southeast and a trough to our west. The trough`s
axis should stretch from the Great Lakes Region down into the lower
MS Valley. The trough will move eastward during the day, pushing the
ridge further offshore. The trough should pass over and to our north
during the evening hours, then deamplify overnight. Additionally,
there appear to be several weak waves/disturbances embedded within
the trough. At the surface, our area will be sandwiched between
synoptic features consisting of a trough inland and high pressure in
the Atlantic. The trough should nudge towards us throughout the day,
helping push the high further offshore. PWATs are expected to start
out below 2", then increase to above 2" by the evening hours. Given
the synoptic setup, instability that will be in place, and the
disturbances in the trough, showers and thunderstorms are a good
bet. We have high end chance values in the afternoon, but this may
be too low. More refinements will be made when this day transitions
into the near term. Heavy rainfall is a concern along with flooding
of low-lying and poorly drained areas. But higher winds aloft may
move these storms along at a good enough clip to limit this
potential. Temperatures will reach their normal values for this time
of year.

Sunday: In the morning the mid-levels will consist of a weak trough
to our north, generally stretching from the Mid-Atlantic States into
the Northeastern States. To our east will be a broad high offshore.
To our west will be a ridge stretching across the Upper and Mid MS
Valley. As the day progresses the weak trough will lift into New
England. The broad high offshore is forecasted to build towards the
coast. Meanwhile, the ridge will move eastward, passing to our north
late at night. At the surface, a trough will be inland. An east to
west stationary front is forecasted to stretch from the Mid-Atlantic
States into the TN Valley, meandering through the day and night.
Meanwhile, high pressure will be in the Atlantic. PWATs will range
from 2-2.15" or towards the higher end of the climo scale for CHS
for this time of year. The setup is similar to Saturday, so once
again we are expecting shower and thunderstorms. POPs are in the
upper chance range and it`s not out of the question they may need to
be raised further. Heavy rainfall is expected. Though, the flood
potential is too early to determine at this point.

Monday: In the morning the mid-levels will consist of broad high
pressure in the Atlantic. This high will connect to a ridge that
will stretch to our north. Meanwhile, a trough will be over the
Plains States. As the day progresses the ridge will quickly move
into the Northeastern States and weaken as the broad high in the
Atlantic tries to strengthen and inch its way towards us.
Meanwhile, the trough will intensify and move eastward, stretching
from the Great Lakes Region into the Lower MS Valley by the
nighttime period. At the surface, low pressure over or near MO in
the morning will move to the Great Lakes Region by the overnight
hours. This low will pull a warm front (already to our north) with
it and drag a cold front to our west towards us. All this while a
trough is just inland of us. And of course high pressure will be
hovering over Bermuda. PWATs will hover ~2". Similar to the weekend,
POPs are in the chance range. Though, they conditions don`t seem as
prime for convection, so they are on the lower end of the range.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
A long wave trough will be over the East Coast while a front slowly
approaches from the west and then passes or stalls over our area.
The current models seem to indicate a wet weather pattern with below
normal temperatures. But it`s still a few days out and more
adjustments are expected.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
VFR. Guidance suggests tstms could be close to KSAV this
afternoon as the sea breeze approaches the terminals. However,
there is not enough agreement on timing/placement in the various
high resolution guidance to support a mention of TSRA just yet
for the 06z TAF cycle. Will reevaluate with the 12z cycle as
additional CAMs can be evaluated by then. No issues are expected
at KCHS.

Extended Aviation Outlook: Brief flight restrictions are
possible due to showers/thunderstorms, mainly in the
afternoon/evening.

&&

.MARINE...
Through Tonight: Typical summer southerly flow regime will
remain in place. Winds will be 15 kt or less with seas 2-4 ft.

Saturday through Tuesday: The coastal waters will be sandwiched
between an inland trough and high pressure in the Atlantic
through early next week. A front will approach the area from the
west towards the middle of next week. The aforementioned
synoptic pattern will lead to mainly southwest winds. The
highest winds are expected Saturday afternoon into Saturday
night due an elevated pressure gradient. Wind gusts at this time
should mostly top out in the lower 20 kt range. Though, a few
gusts could briefly touch 25 kt across the easternmost portion
of the Charleston waters overnight. However, no marine headlines
are expected. Seas during the extended period will generally
peak at 3 ft. The exception will be Saturday due to the winds.
Additionally, there will be the occasional 4 footers near the
Gulf Stream.

&&

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

&&

$$