Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 252035
Area Forecast Discussion
National Weather Service Charleston SC
435 PM EDT Tue Apr 25 2017
Low pressure will move further away from the area tonight, allowing
for weak high pressure to return in its place. High pressure will
prevail across the region Wednesday. A weak disturbance is expected
to affect the area Thursday night, followed by high pressure Friday
into the weekend. A cold front will affect the area Monday.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
An extensive and mostly diurnally driven cumulus and stratocumulus
field will fade with the loss of heating this evening. But it`ll
take a few hours after sunset for clouds over the Charleston quad-
county area to finally diminish, waiting for the last cyclonic
isobar around stacked low pressure over the Great Dismal Swamp and
Virginia tidewater to pull through.
Building heights aloft in response to ridging moving east from the
TN and Ohio valleys, and weak high pressure filling in from the
Atlantic behind the departing low as it heads toward the Atlantic
off the Delmarva, will result in skies eventually becoming
clear/mostly clear across the entire CWFA.
Winds will decouple this evening and will result in adequate
radiational cooling to get temps down to the upper 50s and lower 60s
most communities away from the immediate coast and outside downtown
Charleston. Parts of the Francis Marion National Forecast will
experience the coolest temps, with lows in the mid 50s.
The combination of drier air aloft working it`s way in and lingering
low level moisture could produce some late night fog. But
condensation pressure deficits don`t appear low enough to require an
addition to the gridded forecast at this time.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Ridging aloft will be in place across the Southeast on Wednesday
while weak surface high pressure is in lee of the Appalachians.
The ridging aloft will strengthen Wednesday night as the surface
high weakens/dissipates. Aside from some afternoon clouds, the
weather will be dry. Heights and 850mb temperatures should equate to
above normal temperatures, except cooler at the beaches due to the
afternoon sea breeze.
Thursday ridging will move offshore as a disturbance approaches from
the west. Upper level energy is expected to stay to our northwest
and most of the surface energy will follow this track.
Moisture/instability is forecasted to approach our far interior
counties late in the afternoon and evening. PWATs approaching 1.5"
and BLCAPEs approaching 1,500 J/kg could equate to isolated to
scattered showers/thunderstorms in the afternoon and evening hours.
Some convection could persist into the overnight hours, but the bulk
of activity should dissipate as the best thermodynamics shift to our
Friday ridging across the Southeast will strengthen, leading to a
dry forecast. Temperatures again look to be well above normal due to
warm advection and mostly sunny skies.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Above normal temperatures and mainly dry weather will persist
into Sunday. An upper trough approaches early next week with a
cold front expected to push through Monday and Monday night,
bringing scattered showers/storms.
.AVIATION /21Z TUESDAY THROUGH SUNDAY/...
Outside of a low end risk of fog and MVFR conditions late
tonight/early Wednesday at the airfields, VFR will prevail.
Extended Aviation Outlook: No significant concerns.
Tonight: Low pressure hugging North Carolin and Virginia coasts will
lift slowly NE, allowing for weak high pressure from the Atlantic to
fill in across the local coastal waters. The result is for
slackening W-SW winds at or less than 15 kt and slowly subsiding
seas at or below 3-5 ft.
Wednesday through Sunday: Weak high pressure will be in lee of the
Appalachians Wednesday, weakening/dissipating Wednesday night.
Thursday a weakening system will approach from the west, being
pushed to the north Thursday night into Friday by strong Atlantic
high pressure. The Atlantic high is expected to prevail through the
weekend. With the high driving the weather pattern over the coastal
waters the next few days, mainly southerly winds should prevail.
Diurnal fluctuations are expected with the afternoon sea breeze and
the overnight jet. Seas will generally be 2-4 ft, highest across the
outer GA waters where they could approach 5 ft at times.
Rip Currents...The combination of swell impacting the beaches, an
afternoon sea breeze, and the upcoming Perigean Spring Tide will
generate a Moderate Risk of Rip Currents on Wednesday.
Despite offshore flow, tide levels have remained elevated and since
it won`t take much of a departure (only 0.46 ft at Charleston) to
produce shallow coastal flooding with the evening high tide, we have
gone ahead with a Coastal Flood Advisory for Charleston, coastal
Colleton and Beaufort counties. Levels look to fall just shy of
advisory thresholds further south.
The upcoming Perigean Spring Tide and recent elevated departures
will allow for potential shallow coastal flooding with the
evening high tides Wednesday through Saturday. Coastal Flood
Advisories will likely be required.
SC...Coastal Flood Advisory until 10 PM EDT this evening for