Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1045 am EDT Thursday Aug 21 2014
the region will remain between Atlantic high pressure and an
inland trough of low pressure through Friday. A backdoor cold
front will advance through the area this weekend. High pressure
will then build from the north through the middle of next week.
Near term /through tonight/...
late this morning...other than some patches of middle/high level
clouds across the area most locations are cloud free with
temperatures rising to around 90 already. Overall it looks like a
pretty typical summertime day with deep ridging across much of the
southeast and a pretty nebulous surface pattern in place. We are
on the east side of the upper ridge axis and the models do show
some subtle shortwave energy rotating around within the northwest
flow. Most model solutions keep this afternoon dry and for the
majority of locations this should be true. However...modifying the
12z sounding does result in cape values around 3000 j/kg. This
combined with some weak convergence along the afternoon sea breeze
should be enough for very isolated showers/storms. The pop scheme
remains the same with slight chances concentrated right along the
sea breeze. The main concern for today will be the heat with highs
topping out in the upper 90s to around 100. The ongoing heat
advisory looks good and heat indices will be in the 105-110 range
Overnight we expect mostly clear skies and lows in the middle 70s.
Short term /Friday through Sunday/...
Friday and Friday night...a strong middle and upper level ridge of high
pressure centered over the lower Mississippi Valley will continue to
extend over the region. At the surface...Atlantic high pressure will
prevail as a trough of low pressure lingers inland. The biggest
concern will be the potential for very hot temperatures due to
strong subsidence and a downslope flow...with highs generally
ranging from 98-102. Given that the sea breeze should be pinned near
the coast due to the westerly flow aloft...the hot temperatures will
even extend toward the beaches as well where highs will be in the
middle 90s. The highest heat index values will likely occur along the
coastal corridor where moisture will pool near/ahead of the sea
breeze...with dew points more likely to mix out well inland.
Overall...expect maximum heat index values of 105-112 which will likely
necessitate heat advisories for portions if not all of the forecast
area once again. As for precipitation chances...they appear minimal
given the dry downslope flow and strong subsidence...but could not
rule out an isolated thunderstorm just about anywhere during the
Saturday and Saturday night...the eastern periphery of the upper
ridge will begin to erode as a trough digs southward along the
middle-Atlantic coast. This will drive a backdoor cold front through
the area late Saturday afternoon into Saturday night. Despite
lowering heights aloft and an increase in cloud cover...the
continuing downslope flow and compressional heating ahead of the
front will likely result in highs in the upper 90s to near 100
across much of the area. Heat indices should once again range from
105-112 degrees and the potential need for a heat advisory remains.
The potential for showers and thunderstorms will increase from the
north with the approaching front late in the day...and expand across
the area into the 20-30 percent range Saturday night as the front
Sunday...a moist northeast flow will spread into the forecast area
as surface high pressure wedges in from New England. Expect a solid
chance of showers and perhaps a few thunderstorms. In
addition...temperatures will be considerably cooler...with highs
ranging from around 90 north near the S Santee river to the middle 90s
south near the Altamaha river.
Long term /Sunday night through Wednesday/...
the middle and upper level pattern in the long term period will feature
a strong ridge over the eastern United States. Meanwhile at the
surface...high pressure will continue to build into the region from
the north. This strong ridge appears to Bode well for the region as
medium range guidance is persistent in developing a tropical system
somewhere near the Lesser Antilles and Caribbean Sea. Fortunately
guidance has come into much better agreement showing the potential
tropical cyclone turning well off the southeast coast due to the
strength of the inland ridge. As for expected weather conditions...
there is generally a slight chance of showers/thunderstorms each day
through mid-week...although expect a better chance across parts of
north coastal Georgia given the onshore trajectories in that area.
At night...convection should shift to the coastal waters...but
cannot rule out some convection making it just inland across coastal
areas at times. Temperatures will be near normal through the
Aviation /15z Thursday through Monday/...
VFR conditions will prevail at kchs and ksav through 12z Friday.
Extended aviation outlook...temporary flight restrictions are
possible in isolated/scattered showers and thunderstorms...
especially late Saturday into Monday as a front moves through and
moisture deepens in its wake.
fairly weak SW flow today...then winds increase to 10-15 knots with
some nocturnal surging tonight as the gradient tightens up.
The area will remain between a weak Atlantic ridge southeast of
the area and an inland trough of low pressure into Saturday. This
will result in continued south- southwest winds of 15 knots or less.
However...nocturnal jetting could increase winds upwards of 15-20
knots mainly over the outer Georgia waters Friday night. Seas will be
3 feet or less into the first half of the weekend. A backdoor front
is expected to drop through the area from the north late Saturday
and Saturday night...with high pressure then building from the
north through early next week. Stronger northeast winds are
possible behind the front and could very well result in Small
Craft Advisory conditions for winds and/or seas over portions of
the coastal waters. There is also the possibility that a tropical
system could turn well off the southeast coast and generate some
swells over the coastal waters early next week.
record maximum temperatures...
kchs 100 set in 1983
kcxm 99 set in 1900
ksav 101 set in 1902
kchs 100 set in 1983
kcxm 98 set in 1983
ksav 100 set in 1983
Last time 100 degrees or higher...
kchs June 21 2011
kcxm June 20 2011
ksav July 26 2012
the Charleston SC WSR-88D /kclx/ remains out of service due to a
significant mechanical failure. Repair work continues and the
radar could become operational by late this week or early next
week. Until the Charleston SC radar returns to service...for
Doppler radar coverage of southeast Georgia and south coastal
South Carolina utilize surrounding radars including kjax...kjgx...
kvax...kcae and kltx.
Georgia...heat advisory until 7 PM EDT this evening for gaz087-088-
SC...heat advisory until 7 PM EDT this evening for scz040-042>045-