Scientific Forecaster Discussion
fxus62 kchs 271957
Area forecast discussion
National Weather Service Charleston SC
357 PM EDT Tue Jun 27 2017
a stationary front will linger to the southeast of the area tonight. High
pressure will pass north of the region Wednesday, then shift into the
Atlantic Thursday. A surface trough will develop inland on Friday
and prevail into the weekend.
Near term /until 6 am Wednesday morning/...
through early this evening: convection will focus along 2
separate areas; the more concentrated activity will be south of
Savannah which started along a differential heating boundary and
then merged with the sea breeze. The second will be on the sea
breeze, aided by short wave energy aloft. As a result we are
forecasting isolated to scattered pop's most places, with the
highest chances over coastal Bryan, Liberty, long and all of
McIntosh, where 50% probabilities are shown. The overall
thermodynamics are rather unimpressive, so close to zero risk
for any severe weather. Instead, locally heavy rains of 1-1.5"
in an hours time can occur with weak flow 925-700 mb. We altered
the diurnal temp to show temps down into the mid and upper 70s
where we have our highest rain chances.
Tonight: convection will quickly wind down with the onset of the
nocturnal environment, maybe taking a little longer than is
typical across Berkeley County where the short wave and sea
breeze influences could allow for isolated convection to
persist. Otherwise, Canadian high pressure from the Ohio Valley
will build in with time. Jet stream cirrus/cirrostratus will
occasionally be thick enough to cause some minor impact on the
decline of temps, but even so, lows will fall to the mid and
upper 60s most places inland from US-17, 70-74f along the
coast, near Lake Moultrie and in the immediate Charleston and
Savannah Metro regions.
Short term /6 am Wednesday morning through Friday/...
heights aloft will gradually build through the period as broad
troughing shifts off the northeast coast and weak ridging builds in
from the south. Close proximity to surface high pressure over the
mid-Atlantic will ensure that Wednesday remains dry for most of the
area outside of the Altamaha river region, where subsidence will be
weaker and moisture marginally better.
Moisture will be on the increase Thursday and Friday as high
pressure shifts offshore and low level flow backs more south to
southwesterly, bringing a moist, conditionally unstable airmass back
into the region. Shower and thunderstorm initiation will occur
mainly along the seabreeze corridor each afternoon, but with overall
unimpressive lapse rates, severe threat will remain limited. Have
opted for pops slightly above climo mainly along and south of I-16,
where moisture content will be greatest, Thursday. Moisture will
have overspread the area by Friday as a weak surface through
develops inland, and pops have been maintained slightly above climo
for the entire area to reflect this. Global models are hinting at
the passage of a weak mid-level wave Friday, which may further
enhance convective initiation and coverage.
Temps will be near normal through the period, with most variations
owing to cloud cover and precip coverage.
Long term /Friday night through Tuesday/...
nearly zonal flow will persist aloft with surface high pressure in
the Atlantic. Southerly flow around the high will advect plenty of
moisture into the southeast as an inland trough develops this
weekend. The result will be the typical summertime
shower/thunderstorm pattern with the coverage and intensity trending
upwards each day into the weekend.
Aviation /20z Tuesday through Sunday/...
earlier convection will continue to pull away from ksav, while
upstream convection will stay north of kchs. Thus VFR through
Extended aviation outlook: VFR conditions will prevail. Brief flight
restrictions in showers and thunderstorms are possible at ksav
Thursday, then both ksav and kchs through the end of the week.
tonight: a stationary front will meander S-southeast of the local area,
as Continental high pressure from the Ohio Valley gradually
expands overhead with rising pressures. Easterly winds as high
as 10 or 15 kt this evening will back to NE with some land
breeze influences late, allowing for winds to back around to
the NE at similar speeds. Seas will remain near 2 ft within 20
nm of the coast, up to 3 ft across the eastern half of the outer
Georgia waters. Isolated to scattered showers and T-storms will
occur, mainly through mid evening.
Wednesday 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.
Rip currents: dependent upon how much swell energy reaches the
beaches on Wednesday will determine the exact risk of rip
currents. Since there is uncertainty at this time we prefer to
go with a low risk.