FXUS62 KCHS 271125
Area Forecast Discussion
National Weather Service Charleston SC
725 AM EDT Sat May 27 2017
High pressure will linger over the region through this weekend.
A weak cold front is expected to stall across the area early
.NEAR TERM /THROUGH TONIGHT/...
Today: The mid/upper level flow pattern will feature nearly
zonal flow with a slight anticyclonic curvature. A large area of
NVA will encompass the area and model soundings show plentiful
dry air coincident with a very strong capping inversion. At the
surface, high pressure will be the primary feature as it sits to
the south of the forecast area. Winds for much of the day will
be west-southwest, and this westerly flow combined with rising
heights aloft will result in a warm afternoon. Forecast highs
are in the low 90s everywhere except the beaches which should
see a late afternoon sea breeze. In fact, the Charleston County
beaches will likely see breezy conditions and winds routinely
gusting to around 25 mph.
Tonight: The upper ridge will temporarily flatten in response
to some mid level energy that crosses the southern Appalachians
in the evening. The bulk of any forcing associated with this
shortwave will remain north of the area, but various models do
depict some nocturnal convection along the North Carolina/South
Carolina state line. Current thinking is that this will still
stay north of the Santee River, so a dry forecast is in place,
but it is still something to keep an eye on. Overall still a
quiet night with mild lows around 70.
.SHORT TERM /SUNDAY THROUGH TUESDAY/...
The upper ridge will hold strong for one more day, keeping a
mainly dry forecast for Sunday. The exception may be an isolated
shower or tstm drifting into far northern zones late in the
afternoon as a weak shortwave brushes the area. Highs will top
out in the mid 90s. Given dewpoints around 70, heat indices may
top 100 for a few hours.
The upper ridge will amplify on Monday though the axis will
gradually shift farther into the western Atlantic. Model
soundings show a moderate mid-level cap through early afternoon
after which it breaks. The best shortwave energy will remain
west of the area during the day, though a weak cold front will
push into central GA/SC late. A toasty day with highs in the mid
90s and dewpoints in the lower 70s will yield fairly impressive
CAPE values during the afternoon. There will also be a fair
amount of dry air aloft. If the mid-level cap does indeed break
at some point on Monday, convection should initiate pretty
quickly. There is also the possibility that some upstream
activity will drift into the area. Convective indices would
support some severe thunderstorms, mainly across inland areas
late in the afternoon. Given the uncertainty regarding the
breakdown of the ridge we show pops no higher than 30%.
The cold front will stall near or over the area on Tuesday and
upper shortwave energy will traverse our inland zones. Better
coverage of mainly afternoon/evening showers and thunderstorms
is expected. Greater cloud cover will cut down on surface-based
destabilization though there will still be enough heating to
push CAPEs above 1,000 J/kg. Dry air aloft could create a
damaging wind potential with some of the storms.
.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
A weak front will meander over the area mid to late week while
weak upper troughing will keep a steady stream of shortwaves
moving through. Decent coverage of showers and tstms expected
each day, mainly during the afternoon.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Extended Aviation Outlook: Mainly VFR conditions. Brief flight
restrictions possible in afternoon/evening showers/tstms
Today and tonight: High pressure centered south of the local
waters will drive persistent southwesterly flow through the
period. A locally enhanced pressure gradient as well as the
influence of a late day sea breeze will result in elevated winds
mainly along the Charleston County coast including the
Charleston Harbor. Have capped the forecast at 15-20 knots for
now, but some gusts up to 25 knots will be possible. No Small
Craft Advisory for now, but it could end up being marginally
supportive of one at times. Then overnight, southwest flow will
continue around 15 knots. Seas will primarily be in the 1-3 ft
range through the period, with 4 feet possible out near 20 nm
late today and this evening.
Atlantic high pressure will generally prevail though a weaker
gradient will ensue mid-week as a front stalls over the waters.
Southwest flow will prevail with modest afternoon sea breezes
along the coast.
Tides will be running high through Sunday due to the new moon
and perigee. Fortunately the wind directions are not very
conducive for surge, but we could see very marginal coastal
flooding along the SC coast during the evening high tides today
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