Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
401 am EDT sun Aug 31 2014
high pressure will prevail through at least the middle of the week.
A cold front will likely become stationary north of the region late
in the week...followed by high pressure into next weekend.
Near term /through tonight/...
today...a sprawling Bermuda-Azores surface high will extend west
across the region...while a nearly vertical stacked anticyclone
persists overhead through the rest of the troposphere. For the
most part this will keep any short wave features out of the
forecast area...with a weak capping mechanism to prevail. Despite
this there is considerable moisture within the lower levels of the
atmosphere...and the typical mesoscale-scale boundaries such as the
sea Breeze...Lake breezes and differential heating boundaries.
This combination will have ample instability to help trigger
isolated to scattered showers/T-storms across the forecast area.
The best chances /around 20 percent/ will be over Charleston and
far eastern Berkeley County this morning in association with an
influx of marine air within the best southerly convergent flow.
Then isolated convection looks to form along the sea breeze during
the late morning/early afternoon near and just inland from the
US-17 corridor...before boundary interactions form during the late
afternoon across interior southeast Georgia where 30 probability of precipitation will be common after
3 or 4 PM. Since the overall thermodynamics aren/T that impressive
any severe risk is extremely low...but not zero.
As the morning convective debris clouds from upstream thin out and
dissipate we look for another unseasonably warm day...with 850
temperatures up near 18-19c and the 1000-850 mb thickness as much as
1425-1435 meters. This supports maximum temperatures in the lower and middle
90s...greatest to the west of I-95 in SC and west of US-301 in
Georgia. An onshore synoptic flow and the sea breeze influences will
hold coastal temperatures down to the middle and upper 80s. Associated heat
indices won't be unbearable...but still peaking at 100-105 degrees.
Tonight...the nocturnal stabilization and cooling effects should
allow for convection in the evening to wane. However...convection
may arrive from south of the Altamaha river and this could keep
showers/T-storms going until midnight to 1 am across parts of southeast
Georgia. Late night Atlantic showers/T-storms could again occur in
association with southerly trajectories and ample low level
moisture. Not yet sold on any late night fog...given that
convective debris clouds could linger and the soil temperatures are still
so warm. We/ll only be able to muster lower and middle 70s inland
for overnight lows...while some upper 70s will be common on the
Short term /Monday through Wednesday/...
Monday and Monday night...the center of the west/east oriented
middle/upper level ridge will be positioned directly over the southeast
coast through Monday night. This will place the area between the
best of westerlies and an embedded shortwave to the northwest and a
TUTT-like feature to the southeast over the Bahamas. The surface
pattern will be the definition of typical summertime conditions with
the forecast area under the western periphery of the large
subtropical high pressure over the central Atlantic. The lack of any
larger scale features to hang onto means that precipitation chances
will primarily be driven by mesoscale processes...primarily the
afternoon sea breeze. Model soundings continue to be unimpressive
with some weak capping noted and only 1000-1500 j/kg of cape. Models
have limited coverage of diurnal convection and as such probability of precipitation have
been limited to the 20-30 percent range...favoring southeast Georgia
where some slightly better moisture profiles will reside.
Overnight...any lingering evening convection will dissipate with the
loss of heating and become confined to far inland areas.
Otherwise...the forecast is dry. Look for highs in the low/middle 90s
and lows in the middle/upper 70s.
Tuesday through Wednesday...the overall pattern will not undergo any
significant changes through the middle of the week. The middle/upper
level ridge will evolve a bit...perhaps weakening a bit over the
area on Tuesday...but will begin to strengthen and build back to the
east by Wednesday. At the surface...the expansive subtropical high
over the central Atlantic will remain the most noteworthy feature as
it continues to extend westward across the southeast. No changes
were made to the going forecast which still features diurnal
isolated to scattered showers and thunderstorms. Temperatures will
remain above normal with highs in the low/middle 90s and lows in the
Long term /Wednesday night through Saturday/...
no notable changes were made to the long term forecast as the
pattern continues to favor typical summertime conditions.
Aloft...the primary feature will continue to be the large middle/upper
level ridge and associated anticyclone across the southern half of
the Continental U.S.. similarly...at the surface...the forecast area will
remain under the influence of the western periphery of Atlantic high
pressure. The forecast reflects diurnal isolated to scattered
showers and thunderstorms with above normal temperatures. Forecast
highs are primarily in the low 90s and lows in the low/middle 70s.
Aviation /07z Sunday through Thursday/...
little to no chance for any impacts from rain showers/thunderstorms and rain through 06z
Monday at the airfields. Thus VFR conditions will prevail.
Extended aviation outlook...low chances of direct impacts from
isolated showers/thunderstorms through Thursday. Also...low
chances for early morning fog/stratus. Otherwise...mainly VFR.
today...a large Bermuda Azores high covers much of the western
Atlantic and will extend west across the local waters. After light
and variable winds this morning...the anticyclonic curvature to
the isobars and the sea breeze circulations will generate mostly
gentle southeast winds this afternoon. Much of the wave energy will be in
the form of 2-3 foot swells. Isolated to scattered showers/T-storms
this morning will come to an end for the afternoon.
Waterspouts...conditions appear quite good for waterspouts this
morning and early afternoon...due to light wind fields...ample
moisture and instability...plus favorable lapse rates and
downdraft strength that isn/T too strong. However...we prefer to
wait until we receive early morning satellite images to see if we
have any defined boundaries rather than just isolated convection
for the spouts to develop upon...before addressing this situation
in a marine weather statement.
Tonight...not much change in the synoptic pattern with continued
influence from the sub-tropical Atlantic ridge. There is however
some nocturnal low level jetting that bumps south and SW winds up
to 10-15 knots...but seas still hold around 2 or 3 feet. Isolated
showers/T-storms will redevelop overnight.
Monday through Thursday...the pattern will feature a persistent area
of subtropical high pressure driving a south to southwest flow
through the middle of the week. Winds will generally be less than 15
knots...with some slightly stronger periods possible mainly with the
afternoon sea breeze and nocturnal surging. Seas will generally be
up to 2 feet across the nearshore waters and 2-3 feet for the outer