Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 271133
Area Forecast Discussion
National Weather Service Charleston SC
733 AM EDT Thu Apr 27 2017
A weak disturbance is expected to affect the area tonight, followed
by high pressure Friday into the weekend. A cold front will move
through Monday night, then a stronger storm system will affect
the area mid to late week.
.NEAR TERM /THROUGH TONIGHT/...
As of 725 AM: Latest IR and regional radar indicate that the
middle portion of the convective band over GA has started to
weaken. The weakening trend agrees well with the 4km WRF.
Keeping the CWA dry through late afternoon continues to look
correct. However, debris clouds should push over the inland
counties before thinning or dissipating.
As of 545 AM: Cirrus outrunning the MCS over AL/northern GA/E TN
has started to increase over the forecast area. I will update
the forecast to adjust the sky grids through the rest of the
morning. In addition, inland temperatures have cooled a little
more than in the the current forecast. I will adjust min temps
to at least the recent observations.
As of 3 AM: A north to south band of thunderstorms was pushing
east across AL. Recent sfc observations indicated that dewpoints
in the low to mid 60s were common along and ahead of the deep
convection. Near term models indicate that sfc instability will
steadily increase northward today, become widespread by mid
morning. However, forecast soundings east of the fall line show
a significant inversion center near H75. CAMs indicate that the
convection will survive the crossing of the southern
Appalachians late this morning. In fact, convection is expected
to increase during the mid to late afternoon as it reaches the
Piedmont. Storm motions should gradually shift toward the NE
this evening as H5 ridge remains over the western Atlantic. At
the sfc, the cold front is forecast to slide over the
Appalachians, becoming stationary. Based on forecast moisture
and temperature profiles over the CWA, change in storm motions,
and slowing of the cold front I will reduce PoPs through today.
A few showers and storms may reach the far inland counties late
this afternoon and evening, but should develop very tall. Also,
the deepening mixing and passage of a seabreeze should provide
gusty south winds from mid day until sunset. Using a blend of
temperature guidance, high temperatures are forecast to range
from near 90 over inland GA to the low 80s over the sea islands.
Tonight, a weak but large area of high pressure will become
centered over the mid Appalachians by the pre dawn hours. Low
level south winds will remain steady and the pressure gradient
across the forecast area ranges from 2 to 3 mbs overnight. The
steady return flow should increase sfc dewpoints to the upper
60s to around 70. Weak isentropic flow and increasing llvl
moisture should yield an increasing deck of low stratus,
especially over the inland zones. In addition, weak instability
and low LCLs may allow showers and storms to develop over the
marine zones and portions of the Tri County tonight. Low
temperatures may only reach around 70 degrees over land and the
low to mid 70s over the water.
.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Strong deep layered ridge will hold strong Friday into Saturday,
resulting in dry conditions and well above-normal temperatures.
We expect to see highs climb into the 90s well inland with upper
80s elsewhere but coastal locales. On Sunday as an upper trough
shifts east, upper height falls will bring highs down a few
degrees, and possibly allow for isolated showers/tstms far
.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A mature surface cyclone will lift northeast into the Great
Lakes region Sunday night and Monday, pushing a cold front
through the local area Monday night. A decent channel of
atmospheric moisture ahead of the front will allow scattered to
numerous showers and thunderstorms to move through Monday
afternoon and Monday night. A deeper upper trough moving through
the central United States late week will bring a stronger low
pressure system through the area, accompanied by numerous
showers and tstms.
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
VFR. Mixing is forecast to deepen over 3 kft by noon. Forecast
soundings indicate that momentum transfer should yield frequent
gusts around 20 kts from the south from mid day through the
afternoon. There could be a period during the early to mid
afternoon that the passage of the seabreeze could elevate gusts
into the mid 20s. Winds should decouple around sunset, with
steady winds from south. Low level south winds will remain
steady and the pressure gradient across the forecast area ranges
from 2 to 3 mbs overnight. The steady return flow should
increase sfc dewpoints to the upper 60s to around 70. Weak
isentropic flow and increasing llvl moisture should yield an
increasing deck of low stratus, increasing in coverage during
the pre dawn. The TAFs will feature a TEMPO from 9z to 12z to
indicate IFR ceilings at KCHS and MVFR mist at KSAV.
Extended Aviation Outlook: Low ceilings possible Friday night
and Saturday night. Brief ceiling and/or visibility reductions
possible in scattered showers/storms Monday and Monday night.
A cold front will reach the southern Appalachians late this
afternoon and evening. South winds will gradually strengthen
through mid day, developing frequent gusts into the low 20 kts
by this afternoon. A 2-3 mb pressure gradient is expected to
linger over the forecast area tonight, supporting gusts in the
low 20 kts. In fact, a few periods of gusts in the mid 20s are
possible during the mid evening. Wave heights of 4 to 5 feet
will become common beyond 10 nm by this afternoon. Closer to
shore, wave heights should favor the 2 to 3 feet range. Wave
heights could start to lower slightly late tonight. It is
possible that Small Craft Advisory winds and wave heights could
develop this evening, but appears marginal at this time.
Southerly winds will strengthen Sunday night and Monday ahead of
a strong cold front which in turn will build seas. Small Craft
Advisories likely for most or all of the marine zones during
this period, probably lasting into Monday night.
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 today.
Elevated tides are expected to continue through Saturday, so
more advisories will likely be needed with each evening high