FXUS62 KCHS 202224
Area Forecast Discussion
National Weather Service Charleston SC
624 PM EDT Wed Jun 20 2018
The region will remain between Atlantic high pressure well the
east and an inland trough of low pressure through later this
week. The trough of low pressure is expected to settle over the
region and will likely persist into early next week. A cold
front could push into the region by the middle of next week.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
This evening: Scattered convection west of I-95 ongoing. Due to
multiple boundary collisions and ample CAPE, isolated strong to
severe storms will be possible for the next hour or two. Main
threat with any stronger storms will be strong winds and
possibly small hail. Convection should be over by around 10 pm,
Have tweaked PoPs to match areas well inland expected to receive
convection, but due to relatively low coverage, kept in the
Temperatures have recently fallen considerably into the mid to
upper 80s across many areas, but given very humid airmass, still
expect them to only fall very slowly the rest of the night.
Minimum temperatures by morning will be in the mid to upper 70s
most areas away from the coast. Possibly not going much below 80
within a few miles of the coast.
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
The biggest change in the overall pattern through the rest of the
week and into early this weekend is that the strong mid/upper level
ridge will gradually weaken. The ridge weakens in response to a
strong upper low that models have been persistently showing will form
over the central U.S. and slowly move east-northeast toward the
lower Great Lakes by the end of the period. In addition, deep layer
moisture increases some. The combination of lower mid/upper heights,
better deep layer moisture and some vorticity advection will result
in slightly higher PoPs, generally in the chance range, each
afternoon. The difficulty is that the best moisture does not
necessarily coincide with any weak upper level forcing each day,
which is why we left chance PoPs for mainly afternoon/evening. The
best deep layer moisture looks to be Thursday, but oddly, guidance
is reflecting slightly lower PoPs. Given the lower upper
heights and the potential for some large scale weak upper forcing,
there may be a slightly higher chance for strong to low end severe
storms each afternoon. However, the chances are not enough to
mention in the forecast or HWO at this point.
Temperatures will remain well above normal, but not quite as hot as
last few days as upper heights fall by about 5 decameters. Guidance
showing considerable drop in surface dewpoint temperatures on
Thursday, which seems a little suspect, but did keep upper 60s
inland and lower to mid 70s at the coast. The combination of
slightly lower dewpoints and temperatures will lead to lower heat
indices, but still in the lower 100s likely each afternoon. Lows
very warm, in the mid to upper 70s, to around 80 at the coast.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The upper ridge will temporarily rebuild over the Southeast on
Sunday, causing temperatures to rise back into the middle 90s,
reducing convective coverage, and potentially requiring Heat
Advisories. A substantial upper vort max is forecast to drop
southeast into the area Monday, pushing a weak back door cold
front through the area Monday night or Tuesday. There is
increasing model agreement that temps will be a couple degrees
cooler next Tuesday and Wednesday.
.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
18Z TAFs: Mainly VFR. Showers and thunderstorms have skirted
KSAV, but we will keep at least VCTS mention in there TAF
until ~22Z. Further north, convection has remained far away from
KCHS. But given the convective potential, we'll leave VCTS in
there TAF for now. Conditions are forecasted to quickly
improve late this evening as the convection decreases, with VFR
Extended Aviation Outlook:
Through this weekend: Mostly VFR conditions. However, chances
for afternoon convection will be slightly higher through much of
the period, which will result in slightly higher chances for
brief convectively induced flight restrictions.
Tonight: South winds have increased due to diurnal enhancements
of the mixed layer at the beaches. Speeds should top out in the
15-20 kt range this evening, mainly within 10-15 nm. Winds are
expected to ease to the 10-15 kt range overnight. Seas will
generally average 2-4 ft.
LONG TERM MARINE...(FRIDAY THROUGH THURSDAY)...No highlights
expected through Monday. The marine area will remain between
Atlantic high pressure well to the east and lower pressure over
the land. This will produce southwest winds of mainly 15 knots
or less, highest during the afternoon and near the coast with
the sea breeze, with seas 2 to 3 feet. By the end of the
period/early next week, models are indicating the potential for
a cold front to approach from the north, which could increase
the pressure gradient enough to produce 15-20 knot winds.
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