Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 261944
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
344 PM EDT Mon Jun 26 2017

.SYNOPSIS...
A cold front will slowly push through the area tonight and then linger
off the coast Tuesday. A disturbance aloft will pass through
Tuesday evening, followed by high pressure Wednesday. The high
will shift into the Atlantic by Thursday and extend across the
local area into next weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
A cold front across the area will slowly push offshore as a weak
wave or two of low pressure travel northeast along it. The
deepest moisture and best convergence near the front will be
across far southeast SC near the coast and eastern portions of
southeast GA and this is where we expect some showers and a few
thunderstorms. The best chances will be through early evening
before shifting offshore closer to the higher instability. Can`t
rule out localized flooding and/or damaging winds, mainly
through the rest of the afternoon. Could see some fog develop
overnight as winds subside but much will depend on the position
of the front and amount of cloud cover. Lows should range from
about 65-70 inland to lower to mid 70s at the coast.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
We`ll get a short respite from typical summertime heat and humidity
through mid week, before it slowly starts to make a return Thursday.
Shower and t-storm chances are also below average during this time,
no greater than isolated or maybe scattered coverage to occur.

For Tuesday the cold front will meander off the SE coast, with an
upstream moving through the midwest states. We`re in a rather
nebulous surface pattern between the two features, with a broad
large scale trough situated aloft over the eastern half of the
nation. The main initiator for any convection will be the sea breeze
and a differential heating boundary near the Altamaha River due to
the proximity of the cold front and the southern extension of a
somewhat drier air mass. As such we look for 20-30% PoP`s,
highest south of I-16 where the best moisture exists. I leaned
toward the MOS guidance rather than the slightly warmer low
level thickness forecast, since that is more in line with 850 mb
temps that are below average for late June. Thermodynamics are
unimpressive, but given quite a bit of dry air with the
resulting DCAPE`s in excess of 800-1000 J/kg, plus 0-6 km bulk
shear of 20-25 kt may support an isolated severe risk.

A short wave trough will slide through from the NW around 02-06Z
Wednesday, and with the lack of deep moisture it shouldn`t produce
anything more than isolated showers and t-storms the first half of
the night. This is followed by the southern portion of the Canadian
air mass, that allows for lows to get down to the mid and upper 60s
inland from US-17, lower 70s on the barrier islands and in
downtown Charleston.

Wednesday through Thursday: The broad trough in the east lifts out
and gives way to building heights aloft from a building sub-tropical
ridge centered near the NW Bahamas Wednesday that becomes positioned
about midway between Florida and Bermuda on Thursday. Moisture is
definitely in limited supply Wednesday, with PWat`s as much as 2-3
standard deviations below normal under high pressure covering a good
chunk of the eastern U.S. As the high moves into the Atlantic for
Thursday, return flow brings with it more common PWat`s for
this time of year. The sea breeze is the main driver of any
diurnal convection during this time, and this supports at most
isolated coverage across interior SE GA Wednesday. With better
moisture Thursday we are forecasting 20-30% chances, mainly over
SE GA and for the SC counties near the Savannah River. Below
normal temps will prevail, and comfortable levels of humidity
Wednesday become more typical Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Nearly zonal flow will persist aloft with surface high pressure in
the Atlantic. Southerly flow around the high will advect moisture
into the Southeast as an inland trough develops into the weekend.
The result will be the typical summertime shower/thunderstorm
pattern with the coverage and intensity appearing to increase each
day into the weekend.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
Generally VFR, although there is a low risk of restrictions from
low clouds/showers/thunderstorms at KSAV this afternoon and fog
and/or low clouds at KCHS/KSAV late tonight.

Extended Aviation Outlook: Mainly VFR through Thursday. Maybe brief
flight restrictions in afternoon SHRA/TSRA Friday and Saturday.

&&

.MARINE...
Tonight: A cold front will linger near the coast as a weak wave
of low pressure or two will move northeast along it. Mainly
east/northeast winds will back to north/northeast, remaining
about 10 kt or less (after peaking about 15 kt at times this
afternoon). 2-3 ft seas will subside a bit overnight.

Tuesday through Saturday: A weak pressure pattern Tuesday gives
way to the counter- clockwise flow around high pressure later
Tuesday night through the end of the week. Sea breeze
circulations will give a boost to winds each day, but on
average, speeds will remain at or below 12-18 kt and seas no
greater than 2-4 ft.

&&

.TIDES/COASTAL FLOODING...
Tides could once again approach shallow coastal flooding
thresholds in the Charleston Harbor with the late evening high
tide cycle. Tide levels at Fort Pulaski look to peak just shy of
shallow coastal flooding levels. A Coastal Flood Advisory may be
needed for parts of the lower South Carolina coast, especially
for Charleston County.

&&

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

&&

$$
NEAR TERM...RJB
SHORT TERM...33
LONG TERM...
AVIATION...33/RJB
MARINE...33/RJB
TIDES/COASTAL FLOODING...



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