Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 301543
Area Forecast Discussion
National Weather Service Charleston SC
1143 AM EDT Thu Mar 30 2017
A stationary front across the region will lift north as a warm front
through tonight. A cold front will move through Friday night
followed by dry high pressure into Sunday. Unsettled weather should
return again next Monday, possibly lasting into Tuesday. Dry weather
should then return through Wednesday before rain chances return
.NEAR TERM /THROUGH TONIGHT/...
We will see steady upper height falls today as the upper ridge
gives way to an upper trough pattern. The weak surface high to
the north is beginning to shift east while the stationary front
along the Altamaha River will start to lift north late today.
The low-level onshore flow has increased surface dewpoints into
the mid to upper 60s. Aloft, the 12Z raob shows considerable dry
air which is limiting the overall precipitable water and depth
of ongoing convection. The lack of significant upper level
features today indicates the convective pattern will be
dominated by mesoscale influences. Since daybreak we have seen
two main convergence axes, one across Charleston County and the
other across our western GA zones. Extensive cloud cover in
these areas is limiting insolation and thus boundary layer
destabilization. Meanwhile, the middle part of the forecast area
has seen partly sunny skies this morning and temps rising into
the low 80s. There will be ample differential heating boundaries
and eventually a sea breeze boundary to allow additional showers
and isolated tstms to develop today. The severe wx threat
appears fairly low since the cloud cover has been limiting
instability. Perhaps an isolated storm could develop in the
central areas where a bit more SB CAPE is developing and DCAPE
will be around 1000 J/kg.
Tonight: Wind fields will continue to build above the surface
inversions with the flow becoming southerly overnight in the
wake of the warm front passage. Scattered showers and a few
thunderstorms overnight will tend to increase from the west
late with the approach of a strong upper wave which is expected
to both weaken a bit and slightly tilt negatively as it moves
through the lower Gulf Coast region. Overnight, the potential
for organized convection appears best to our west. Severe
potential will be marginal at best until late given the forecast
shear but weak elevated instability. We raised temps tonight,
in the mid to upper 60s most areas.
.SHORT TERM /FRIDAY THROUGH SUNDAY/...
A cold front will approach Friday and then push through later Friday
and Friday night. Showers and some storms are expected Friday
morning, especially inland and across SC, as a shortwave moves
through. Conditions will then improve as deeper moisture shifts
offshore. Although wind fields will be strong Friday, instability
appears minimal and thus the threat for any severe storms is quite
low, mainly confined to SC. Either way it should be a breezy day
with gusts up to around 25-30 mph. Dry weather is on tap through the
weekend as high pressure builds in.
Despite the slight cool down behind the front for this weekend,
temperatures should remain above normal through the period.
.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Dry high pressure to prevail through Sunday night although moisture
will be increasing Monday morning as low-level jetting ramps up
ahead of approaching low pressure from the west. Looks like a good
shot of showers and storms Monday and Monday night as low pressure
passes by to the northwest of the area. Could be another high
shear/low CAPE situation and a few severe storms might be possible.
Things should clear out by Tuesday but the ECMWF still indicates a
few showers possible, mainly across SC. High pressure will then move
in through Wednesday before another storm system likely moves across
the Deep South and brings rain back to the area Wednesday night into
Thursday. Temperatures should remain above normal through the
.AVIATION /16Z THURSDAY THROUGH MONDAY/...
KCHS: Low level winds were increasing and the stratus had lifted
to stratocumulus and MVFR should be persistent overnight. Fog
potential is unlikely given the latest trends and winds in the
forecast soundings. There is some uncertainty how quickly cigs
will rise above MVFR levels Thursday morning, but data generally
support a 14-15z timeframe. Convective rains are certainly later
in the day but until then, only shallow showers are possible.
KSAV: The primary concern is low-stratus and fog. Low-level
moisture will steadily increase from off the Atlantic tonight as
a stationary front lingers near the Altamaha River. The terminal
looks to become embedded within the corridor of highest surface
dewpoints so expect extensive low-stratus and possibly some fog
(stratus build down) to occur. Will go ahead and show prevailing
IFR cigs right at alternate minimums and MVFR vsbys 07-14z with
a tempo group 08-12z with LIFR cigs and IFR vsbys. There is a
potential for lower conditions, including conditions below
airfield minimums, but it still appears the boundary layer
winds will be too strong to support this. This will be monitored
carefully and amendments issued as needed. Similar to KCHS,
there is some uncertainty how quickly cigs will rise above MVFR
levels Thursday morning, but data generally support a 14-15z
EXTENDED AVIATION OUTLOOK: Restrictions likely due to
showers/thunderstorms/low clouds Friday morning and again Monday
and Monday night. Breezy conditions are also expected Friday.
Today: High pressure centered well to the north will move east
and maintain an onshore flow over the waters, strongest over
Charleston waters where the gradients remain tighter. The flow
should begin to veer more to the SE later today while seas
range from 3-5 FT north to 2-4 FT south. The veering flow will
remain modest tonight a in warm air advection regime, increasing
to 15-20 KT and 15 KT near shore GA waters. Seas should
continue to respond and SCA conditions may develop over
Charleston Waters by this evening or perhaps later tonight as
seas touch 6 FT just beyond the pilot buoy. SCA conditions are
also possible over outer GA waters where seas build to 6 FT out
near the Gulf Stream.
Friday through Tuesday: A cold front will move through Friday
night/early Saturday. Advisory conditions likely Friday from the
outer GA waters northward into the SC waters into Friday night
mainly for seas building to 6-7 feet, highest toward the Gulf
Stream. Cannot rule out some sea fog over the near shore waters
until the cold front passes later Friday/Friday night. Conditions
will go downhill again Monday as a storm system approaches from the
west and Advisories will be possible Monday into Tuesday, at least
for the offshore GA waters and SC waters.
Rip Currents: Moderate risk for rip currents along the SC coast
today. Onshore winds along with a 2-3 foot long period swell
may produce rip currents. The enhanced risk for rip currents
could persist into Friday.
Given a 0.7-0.9 ft anomaly with the last two high tides, shallow
coastal flooding looks all but certain along the SC coast late
this evening. Therefore we issued a Coastal Flood Advisory with
expected levels of 7.3-7.6 ft MLLW. Chances are lower that the
Ft Pulaski gage will reach 9.2 ft MLLW though it will definitely
be close. We will hold off on issuing an advisory there until
trends can be monitored further.
SC...Coastal Flood Advisory from 9 PM this evening to midnight EDT
tonight for SCZ048>050.