Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 070426
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1226 AM EDT Tue Apr 7 2020

.SYNOPSIS...
High pressure will prevail tonight. A series of upper level
disturbances will pass through Tuesday and Wednesday. A cold
front will move through Thursday, eventually followed by high
pressure.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Very minor changes were made to hourly temperatures for the
midnight update.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/...
A broad upper ridge will remain to our west on Tuesday while
several potent shortwaves moves through the local area. A decent
plume of deep moisture will move in from the west during the
early afternoon hours, pushing PWATs above 1.6" in most areas.
Although the strongest upper vorticity will move through
southeast GA, greater surface-based instability and stronger
mid-level lapse rates will exist over central and southern SC.
Even still, only 500-1,000 J/kg CAPE are forecast over these
areas. There should be ample forcing for at least scattered
showers and thunderstorms developing over inland areas and
spreading east through the afternoon. Given 50 kt of 0-6 km bulk
shear, convection could become slightly organized over southern
SC later in the day, though the instability appears too weak to
support a more significant severe weather episode. High
temperatures will reach the low to mid 80s.

A fairly similar pattern will exist on Wednesday though there
appears to be less shortwave energy to work with. Additionally,
850 mb flow veers to a more WNW direction which favors downslope
flow and low-level subsidence. This could limit the potential
for convection so we show slightly lower PoPs than on Tuesday.
The downslope compression will push high temps into the middle
80s all but the immediate coast.

Thursday will be quite warm due to compression ahead of an
approaching cold front. Broad westerly flow will really limit
the potential for convection ahead of the front. Highs will
reach the upper 80s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Models continue to vary a lot in the long term forecast. They appear
to show the cold front moving through Friday, but they disagree on
whether it will be drenching rains or a mostly dry day. We were
forced to go with a blend of the models again. Friday night into
Saturday the forecast appears to be more dry than wet with cooler
temperatures. But then the models diverge drastically for Sunday.
Expect more changes to the long term forecast as the models
hopefully come into better agreement.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
VFR. There will be a risk for showers/tstms this afternoon, but
it remains unclear this far out whether direct impacts to either
KCHS or KSAV will occur. No mention will be included in the 06z
TAF cycle, but will be reevaluated for the 12z TAF cycle.

Extended Aviation Outlook: Gusty winds are possible each
afternoon through Thursday. Showers could bring brief flight
restrictions each afternoon through Saturday.

&&

.MARINE...
Tonight: High pressure that is initially centered atop the
Georgia waters will slip a little more southeast, keeping a
decent gradient in place locally. That will allow for S and SW
winds to reach as high as 15 to 20 kt on the AMZ350 waters, 10
or 15 kt elsewhere, including Charleston Harbor. Much of the
wave energy will be in the form of easterly swells every 11-=13
seconds, averaging 2-4 ft within 20 nm of shore and up to 5 ft
on the outer Georgia waters.

Tuesday through Saturday: A somewhat enhanced SW gradient will
exist between offshore high pressure and an inland trough. A
gusty sea breeze will occur each afternoon/evening along the
land/sea interface. Cannot rule out brief windows of Small Craft
Advisory conditions in Charleston Harbor due to the sea breeze.
Elsewhere, winds should top out at 15-20 kt.

Rip Currents: Ongoing astronomical influences, a fairly strong
sea breeze and long period, easterly swells of 12-13 seconds
will support a Moderate Risk for rip currents at all beaches
through Tuesday evening.

&&

.TIDES/COASTAL FLOODING...
Higher than normal tides are expected most of this week due to
astronomical influences from the upcoming full moon and perigee.
Additionally, winds are forecast to be onshore at times with
ocean swell, which would further elevate the tides. As a result,
minor to perhaps moderate coastal flooding is expected with
each high tide through Friday. Coastal Flood Advisories will be
needed.

&&

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

&&

$$



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