Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 281644

Area Forecast Discussion
National Weather Service Charleston SC
1244 PM EDT Wed Jun 28 2017

High pressure will pass north of the region this afternoon,
then shift into the Atlantic Thursday. A surface trough will
develop inland on Friday and prevail into the weekend.


We tweaked hourly temps and dew points ever so slightly based
on latest trends, and we lowered a few spots south of I-16 by a
degree for max temps since cloud cover is thickest those

This afternoon: Flat ridging will prevail aloft as Canadian
high pressure at the surface over Virginia shifts east to the
Delmarva area. Large scale subsidence, the lack of moisture
(where PWat`s are no more than 70-90% of normal) and limited
thermodynamics point toward an atypical late June day void of
much if any convection, below normal temps and for many places
comfortable humidity levels.

The sea breeze and differential heating boundaries are the only
mechanisms for showers/t-storms. So we have nothing more than
isolated convection during the mid to late afternoon south of
Claxton where there is a little better moisture and boundary
interactions. But would not be surprised to get by with a
completely rainfree forecast.

850 mb temps are at least 1-2 standard deviations below late
June norms, and with jet induced mid and high clouds, plus
diurnally driven cumulus cutting down some on insolation, max
temps today will fall shy of 90F, or about 2-4F below
climatology. Combined with dew points mainly in the 60s will
result in RH levels down into the 40-60% range.

Finally, deep mixing and a modest sea breeze will boost E winds
up as high as 10-15 mph far inland, 15-20 mph and gusty near the

Tonight: Moisture will begin to improve, mainly for southeast
Georgia near the Altamaha River. Models even depict the
development of a weak coastal trough late tonight. Weak
convergence along the line and within some coastal speed
convergence in the onshore flow will likely result in increasing
coverage of showers and thunderstorms along the Georgia coast
and Atlantic waters by late. PoP`s continue to be in the 20-30
percent range. Lows will fall into the upper 60s in the far
north, ranging to the low 70s elsewhere.


Heights aloft will gradually build through the period as weak
ridging builds in from the south. Moisture will be on the
increase Thursday as surface high pressure shifts offshore and
low level flow backs to south to southwesterly, bringing a
moist, conditionally unstable airmass back into the region.
Shower and thunderstorm initiation will occur mainly along the
seabreeze corridor, but unimpressive lapse rates could limit the
severe threat. However, models continue to show a weak mid-
level wave passing across the area late Thursday, which would
enhance convection/coverage and increase the severe threat.
Given the uncertainty of the wave timing, kept POPs slightly
above climo Thursday, mainly along and south of I-16, where the
most moisture will be in place. Moisture will have overspread
the entire area Friday as a weak surface through develops
inland. The same is expected on Saturday, so POPs remain
slightly above climo for the entire area to reflect this. Storm
initiation is expected each afternoon along the sea breeze.
Temps will be near normal through the period, with most
variations owing to cloud cover and precip coverage.


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
shower/thunderstorm pattern.


Although isolated SHRA/TSRA will be near the KSAV terminal close
to 18Z Thursday, VFR conditions are forecast there and at KCHS
with the 18Z TAF set.

Extended Aviation Outlook: Brief flight restrictions possible
in showers/thunderstorms at KSAV Thursday, then both KSAV and
KCHS into the weekend.


This afternoon: Continental high pressure centered in Virginia
will slide into the nearby Atlantic, as a stationary front
lingers across the Florida peninsula. Winds will clock around
to the E, and with a boost from the sea breeze speeds will reach
as high as 15-20 kt. The favorable onshore will allow seas to
build as large as 3-4 ft, with even some 2 foot waves at times
in Charleston Harbor.

Tonight: No real change overnight, with prevailing easterly
flow. Seas will be in the 2-4 ft range, highest beyond 20 nm.

Thursday through Sunday: 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. Seas
will remain mainly in the 2 to 3 foot range in small southeast
swell and minor local windswell.




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