Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 170152
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
952 PM EDT Wed Aug 16 2017

.SYNOPSIS...
Atlantic high pressure will remain in control as troughing
persists inland through late this week. A cold front will
approach this weekend, likely falling apart early next week as
high pressure returns.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of around 945 pm most showers have ended but with a surface
trough lingering near the Charleston Tri- County area there could
be a few showers and/or storms late tonight. Otherwise the warm
and muggy conditions will persist with lows close to 80 most
locales, generally warmest near the coast.

Note: Assuming the temperature does not drop below 78 degrees
at Charleston Airport (KCHS) prior to 1 am, the record high
minimum for the date will be tied. See Climate section below for
more details.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
Thursday: A ridge axis will stretch from the Northeastern states
into the Mid-Atlantic states. Aloft, broad high pressure is
forecasted to hover over the Deep South. At the surface, a weak Low
should form over the Midlands in the afternoon while troughing
persists further inland. Deep moisture is in place with PWATs
getting up to 2.3". This is 1-2 standard deviations for this time of
year. Models indicate good instability in place by the afternoon
with GFS BLCAPEs approaching 2,000 J/kg, a Showalter Index nearing -
4, and decent lapse rates. Even with some subsidence aloft from the
aforementioned high, showers and thunderstorms are expected to
develop in the afternoon. DCAPEs should exceed 500 J/kg, so some of
the stronger storms could produce gusty winds in additional to
locally heavy rainfall. Temperatures will be in the low to mid 90s
with Heat Indices as high as 106-108 degrees. Not quite enough for a
Heat Advisory, but certainly making for unbearable/uncomfortable
outdoor conditions before the convection begins. The convection
should dissipate into the evening as the atmosphere stabilizes, but
more convection is expected to develop over the coastal waters. It
will be a very warm night with lows in the mid to upper 70s.

Friday and Saturday: The ridge axis shifts offshore Friday as
troughing builds from the Great Lakes Region into the TN Valley by
Saturday. A the same time, the broad high pressure over the Deep
South will retreat to TX. At the surface, troughing is expected to
persist inland. A cold front is also expected to approach from the
northwest on Saturday. Deep moisture remains in place with PWATs
above 2.0", perhaps getting up to 2.3" at times. Instability
increases each of the two days along with lift from the approaching
front and the sea breeze. Showers and thunderstorms are expected,
some being enhance by cold pool boundaries. The overall severe risk
is low, but the strongest storms could produce damaging winds. Heavy
rain is also a threat, but maybe less so on Saturday as steering
level winds start to increase. Highs will be several degrees above
normal.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
A cold front upstream will attempt to approach but will likely fall
apart as it runs into a strong blocking ridge both surface and
aloft. The typical instability along with sufficient moisture and
meso-scale boundary interactions will support a chance of mainly
diurnally driven convection each day through the extended period,
including Monday the day of the total solar eclipse. Above average
heights, 925 and 850 mb temps and low level thickness will allow for
a continuation of above normal highs and lows.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Mainly VFR outside any showers/thunderstorms, mainly Thursday
afternoon.

Extended Aviation Outlook: Temporary flight restrictions can occur
in scattered diurnal convection through early next week.

&&

.MARINE...
Tonight: South to southwest winds will become uniformly
southwest overnight. Speeds will remain 15 kt or less with seas
2-3 ft.

Thursday through Saturday: The coastal waters will lie in a general
SW`erly flow along the fringes of Atlantic high pressure, as a
Piedmont trough persists inland over the SE. While afternoon sea
breeze influences and nocturnal low level jetting will give a boost
to winds, speeds on average will be no more than 15-18 kt. Seas will
hold at or below 3 or 4 ft. Expect isolated to scattered showers and
t-storms through the entire period.

Sunday through Monday: A cold front upstream will never reach the
waters as high pressure holds firm, keeping winds and seas below any
SCA conditions. Isolated to scattered showers and t-storms will
again prevail.

&&

.CLIMATE...
Record high minimums for 16 August...
KCHS 78/2010
KCXM 83/2016
KSAV 78/1942

Record high minimums for 17 August...
KCHS 78/2010
KCXM 82/2010
KSAV 78/1995

Record high minimums for 18 August...
KCHS 78/2010
KCXM 82/1998
KSAV 78/2010

&&

.EQUIPMENT...
The temperature sensor at the Downtown Charleston observation
site (KCXM) has failed. Technicians are working to resolve the
problem. Temperature and dewpoint data will not be available
until the sensor is replaced.

&&

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

&&

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



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