Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 270526
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
126 AM EDT Tue Jun 27 2017

.SYNOPSIS...
A cold front will linger off the coast through 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 THIS MORNING/...
No major changes.

&&

.SHORT TERM /6 AM THIS 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 /06Z TUESDAY THROUGH SATURDAY/...
Generally VFR. Could see a brief period of MVFR vsbys from
fog/stratus at KSAV just before sunrise where dewpoints are
higher.

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 10 to 15 kt at times this
evening). 2-3 ft seas, highest Charleston waters and offshore.

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...
Coastal Flood Advisory has expired.

&&

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

&&

$$


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