Scientific Forecaster Discussion
fxus62 kchs 282342
Area forecast discussion
National Weather Service Charleston SC
742 PM EDT Wed Jun 28 2017
high pressure to the north will move into the Atlantic tonight and
Thursday. A surface trough will develop inland on Friday and prevail
into the weekend. A deteriorating cold front will approach the area
early next week.
Near term /until 6 am Thursday morning/...
as of 725 pm: the sfc pattern will feature ridging Carolina
high pressure centered over the western Atlantic and low
pressure over la, supporting east-southeast winds through tonight. An
isolated showers developed along a convergence line over Liberty
County, with a few showers over amz374 and 354. I will update
the forecast to add isolated showers to the forecast.
while we can't entirely rule out a stray shower along the sea
breeze and other meso-scale boundaries over far inland southeast Georgia
near the Altamaha river, for the most part it will remain
rainfree with scattered-broken cumulus and scattered-broken
cirrus/cirrostratus. Temps will slowly fall to the upper 70s and
lower 80s by sunset.
For tonight, surface high pressure off the the Virginia Tidewater
will slide further east into the Atlantic, as a short wave
ridge attempts to amplify a little further. While the low level
trajectories from the east and southeast will allow for a gradual return
of moisture from off the Atlantic, the layer from 850-400 mb
remains essentially void of moisture. This suggests little risk
of any showers, although with isentropic ascent developing, and
a weak mid level impulse drifting in from the SW late in tandem
with some coastal convergence, there might be a few showers or
low topped T-storms over McIntosh County and maybe coastal
Liberty County closer to daybreak.
Once diurnal cumulus fade this evening, the jet induced high
level clouds will gradually diminish in areal coverage as the
southern branch of the jet pulls away. This will support skies
becoming mostly clear north and partly cloudy south. But with
the approach of an impulse aloft overnight and moisture flux
convergence, clouds will increase yet again, so that by daybreak
skies will be mostly cloudy south, at least partly cloudy
Temps will end up near or slightly below average for late June,
ranging from the mid 60s in the Francis Marion to upper 60s and
lower 70s most elsewhere. The exception will be coastal areas
and in downtown Charleston where mid 70s will be common due to
the onshore flow.
Short term /6 am Thursday morning through Saturday/...
gradually building ridge remains overhead through the period as
surface high pressure slides eastward from the mouth of the
Chesapeake Bay. Deep layer moisture will fill in across the area
during the day on Thursday, and remain in place into the weekend.
Convective initiation will mainly be along the sea breeze corridor
each afternoon, though there are a couple of features of note which
could spell an increase in precip coverage and intensity. Shortwave
energy rounding the periphery of the upper level ridge will pass
inland of the area during the day Thursday, and could provide some
destabilization locally, especially along and west of US Highway 301, or
more likely allow ample convection to Blossom over the Piedmont,
which could then either advect toward the coast through the evening
or encourage boundaries to trigger further convection locally.
Additionally, models are indicating that a weak mid-level wave - the
manifestation of a defunct low formerly over the Gulf Coast - may
provide convective enhancement Friday, especially inland. Above
climo pops have been maintained to account for these features. The
typically waning of convective activity overnight is expected.
Temps will remain below normal through the end of the workweek
owing to onshore flow and ample cloud cover, before returning to
near normal this weekend as a more humid airmass fills in.
Long term /Saturday night through Wednesday/...
high pressure will prevail in the Atlantic while a surface
trough persists inland. Southerly flow around the high will keep
plenty of moisture advecting into the southeast during this
time period. The result will be the typical summertime
Aviation /00z Thursday through Monday/...
VFR conditions expected through the 0z taf period. The sfc
pattern will feature ridging Carolina high pressure centered
over the western Atlantic and low pressure over la, supporting
east-southeast winds through the period. Winds may become marginally gusty
during Thursday afternoon. A weak front is forecast to lift
toward the mouth of the Savannah River during the daylight hours
Thursday. Guidance is divided on the convection potential along
and north of the front. However, I will highlight the limited
potential for tsras with a prob30 from 17z-22z.
Extended aviation outlook: persistent onshore flow advecting a
maritime airmass into the area could bring flight restrictions in
low ceilings Thursday night and Friday morning, thought there is
still significant disagreement amongst guidance. Brief flight
restrictions are also possible in mainly afternoon
showers/thunderstorms at both ksav and kchs through the weekend.
tonight: a 1023 mb high centered to the NE of the Great Dismal
Swamp will pull east, with its associated ridge axis extending
west-SW across the Carolina's. This supports an easterly flow as
high as 15-20 kt this evening due to sea breeze circulations,
before the gradient slackens overnight and speeds drop to less
than 12 kt before sunrise. The long onshore fetch will allow for
seas of 3-4 ft this evening, dropping about a foot by morning
as the wind speeds decrease.
Friday through monday: high pressure sliding from the mid-
Atlantic coast to its more seasonally typical Bermuda high
location will remain in control through the period. Expect
mainly light to moderate breezes, with the usual summertime sea
breeze wind enhancements near the coast in the afternoon, and
possible brief periods of gusty winds around daybreak. Seas will
remain mainly in the 2 to 3 foot range in small southeast swell
and minor local windswell.