Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 291121
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
721 AM EDT Mon May 29 2017

.SYNOPSIS...
High pressure will linger over the region today before a weak
cold front gradually sags south into the area. Atlantic high
pressure will extend west over the region late week into the
upcoming weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Zonal flow aloft will become more west-southwesterly
through the day as the mid/upper level ridge becomes more
centered over the tropical Atlantic. For much of the day, a
large area of NVA will sit over the region before some channeled
vort energy draws closer in the evening. At the surface, a weak
surface trough will take shape across the central Carolinas and
central Georgia. Westerly low level flow will prevail early
before turning more southwesterly with time as the sea breeze
moves inland and the surface trough becomes better defined. The
main forecast question revolves around thunderstorms chances and
any severe weather potential. Models show good agreement that
most of the upcoming day will be dry with a strong capping
inversion noted on model soundings. This matches up well with
the NVA aloft. Then late in the afternoon, the cap weakens and
shortwave energy embedded within the west-southwest flow aloft
begins to impact the area. Model consensus is that an area of
convection will develop within the surface trough over central
and north Georgia and then push to the east. As such, it looks
like the daytime hours will be dry. Highs are expected to rise
into the low to mid 90s, but increasing high clouds could keep
temperatures down a degree or two in some areas.

Tonight: The big question during this time is what upstream
convection develops and what is it`s state as it moves closer to
the forecast area. It appears we will be dependent on
convection moving in for rain chances, as there will not be any
real initiating features across the forecast area. Therefore,
confidence is low in coverage and intensity for the evening and
early overnight hours. PoP`s have been limited to the 20-30
percent chance range. The overall near storm environment isn`t
overly impressive, especially when considering that any impacts
would likely be after sunset in the absence of surface heating.
Mid-level lapse rates should be between -6 and -7 C with LI`s of
-5 to -6. DCAPE values will likely be in excess of 1000 J/kg,
 but instability will probably not be rooted in the surface. The
 marginal risk in place by SPC seems quite reasonable given
 that the overall coverage will be isolated to scattered at
 best. But, we could still see a couple of strong to marginally
 severe storms capable of damaging wind gusts and hail. The main
 time period would be roughly 7-11 pm. PoP`s shift to the east
 and diminish through the night. Lows are only expected to fall
 into the low 70s.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
Tuesday should be more active than prior days due to increasing
shortwave energy affecting the area and a weak front sagging
southeast into the area. High temps around 90 and dewpoints
close to 70 will contribute to moderate CAPEs of 1500-2000 J/kg
in the afternoon. Mid-level lapse rates will be decent and some
dry air will exist aloft, supporting decent cold pools. 0-6 km
shear will be around 25 kt which is marginal but could support
some storm organization. The best severe weather potential looks
to be inland closer to the better upper level energy.

Wednesday will be fairly similar to Tuesday though mid-level
flow will be veering, potentially resulting in more capping that
could limit convective development. Instability parameters are
also expected to be weaker. Isolated to scattered tstms expected
to develop in the afternoon. Severe weather potential looks
relatively low though an isolated severe storm will be possible.

Subtle shortwave ridging may produce some NVA on Thursday and
the surface front may push just southeast of the region.
However, decent low-level moisture and warm temps will produce
at least some surface-based instability. Convection potential is
somewhat nebulous for Thursday though we trended pops downward
a bit.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Friday through Sunday may feature higher coverage of showers
and tstms mainly in the afternoon and evening as a series of
shortwaves moves through the Southeast and a lee surface trough
exists inland. A more pronounced cold front could affect the
area Sunday or Monday, though the front may not end up making it
this far south.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
VFR will prevail at both KCHS and KSAV. Thunderstorms could
develop this evening and impact the area, but confidence in
direct impacts at either terminals is quite low.

Extended Aviation Outlook: Mainly VFR conditions. Brief flight
restrictions possible in mainly afternoon/evening showers/tstms.

&&

.MARINE...
Today through tonight: Westerly flow early on will shift to
south and southwesterly through the day and remain southwesterly
through the overnight. Wind speeds may increase into the 15 knot
range this afternoon, highest along the land/sea interface and
in the Charleston Harbor where winds will likely be 15-20 knots.
Overnight, winds will mainly be in the 10-15 knot range. Seas
will generally be in the 2-3 ft range.

Fairly weak winds and small seas are expected to persist over
the Atlantic waters and Charleston Harbor Tuesday through
Saturday. Weak Atlantic high pressure will linger off the coast
with a subtle front stalled just inland. The sea breeze will be
fairly weak Tuesday through Thursday, then potentially a bit
stronger Friday into Saturday as the Atlantic ridge strengthens.

&&

.EQUIPMENT...
The temperature sensor at KSAV is running high during the
daytime hours. Use this data with caution, especially during
peak heating. The high temperature has been set to missing for
today. Technicians have been notified.

&&

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

&&

$$

NEAR TERM...BSH
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...BSH/JRL
MARINE...BSH/JRL
EQUIPMENT...


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