Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 251956
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
356 PM EDT Sun Jun 25 2017

.SYNOPSIS...
A cold front will gradually move through the area tonight, then linger
just offshore through Tuesday. High pressure will build in from the
northwest by mid week bringing drier conditions before moving into
the Atlantic for the second half of the week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
A highly amplified upper pattern will take hold tonight,
featuring a broad trough in the eastern half of the country and
ridging in the inter-mountain west. We still have the sub-
tropical ridge from Bermuda across Florida that attempts to hold
on, but weakens ahead of subtle short waves that ride quickly
E-NE through the flow aloft between the anticyclone and the
large scale trough. As a result there are slow height falls
through the night. Meanwhile, a cold front continues to struggle
to the SE, and is still found off just to the W-NW of the CWFA
as of early this evening. But with the height falls and a nudge
from high pressure in the central Plains that pokes east, the
front should limp through and reach near the coast by daybreak
Monday.

There remains a huge swath of Pwat`s around 2.2-2.3 inches from
the Gulf of Mexico, around 120-130% of normal in advance of the
front. The moisture extends through the entire troposphere and
will support the risk of at least minor to moderate flooding
concerns this evening, with rainfall rates on the order of 2-3
inches an hour. The MCS over the local area has cloud top temps
as cold as -65 to -75C across a large chunk of our zones which
would support at least a few Flood Advisories, mainly for the
coastal corridor through 7 or 8 pm. But flash flooding seems
unlikely, and we are fortunate to be coming out of low tide.
Heavy rainfall continues to be mentioned in the ZFP and grids.

While we have seen one storm in Beaufort/Jasper County region,
the overall risk of severe weather remains limited due to poor
lapse rates, the wet environment and DCAPE generally less than
800 J/kg. Still, isolated wet microbursts with winds of 40-50
mph may still occur where boundary collisions occur this
evening.

We continue to show likely or categorical PoP`s for all but the
Allendale, Screven, Jenkins counties where we still have high-
end chance. Coverage will diminish from W-NW to E-SE during the
late evening and overnight hours, with slight chance/chance
probabilities for the post-midnight period.

There are hints of low stratus per soundings and certain MOS
guidance and even 30% SREF probabilities of fog late tonight.
But condensation pressure deficits don`t appear low enough, so
no mention of reduced visibilities over land areas at this
time.

The temperature curve has been greatly altered due to the
extensive convection and the resulting diabatic cooling. But
due to the lack of any CAA behind the front we don`t foresee
anything any lower than the lower or middle 70s for minimum
temperatures.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
A cold front is expected to move southeast through the area early
Monday before stalling just offshore through Tuesday, then pushing
farther southeast Wednesday as high pressure builds from the
northwest. Rain chances will remain elevated Monday for most areas
except toward the Pee Dee/Midlands as the deeper moisture/forcing
begins to shift offshore. Low rain chances for generally light
precipitation will continue however into Wednesday, although by
Wednesday chances will mostly be confined to the GA coast where
coastal convergence will be enhanced. Otherwise temperatures will
warm to near normal into Tuesday before the drier and cooler air
mass arrives for Wednesday.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
The center of High pressure will move offshore of the NC Outer Banks
Wednesday night, and drift further east and out to sea through
Saturday. Southerly flow will develop across the Southeast during
this time period. Temperatures will trend back to normal and
moisture will increase, bringing a return to the typical summertime
shower/thunderstorm pattern. The risk of showers/storms appears to
increase each day into the weekend.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
There remains a high probability of SHRA/TSRA impacting both
terminals into this evening as a cold front sags into closer
proximity to the terminals, with MVFR and possible IFR most of
the time through 02-03Z Monday. Occasional heavy rains and maybe
even some moderate wind gusts will occur in the convection
through 22-23Z.

There are indications of low stratus late tonight into Monday
morning, but probabilities are low enough where we don`t need to
show anything worse than scattered clouds around 1500 ft at this
time.

With a cold front lingering nearby through Monday, showers are
still possible at times after the deep convection wanes this
evening. But significant impacts are not anticipated at this
time.

Extended Aviation Outlook: Flight restrictions are possible at times
through Tuesday, mainly due to showers and thunderstorms although
some fog will be possible Monday night.

&&

.MARINE...
Tonight: The general synoptic pattern does show a S-SW flow
around the Atlantic ridge and in advance of the cold front,
before land breeze influences and the approach of the cold front
allows for veering winds overnight. On average winds will hold
below 15 kt with seas 2-3 ft. But given numerous or even
widespread convection, wind fields will become altered at
times. Mariners should be prepared for lightning strikes, gusty
winds, reduced visibilities in heavy rains and occasional higher
winds and seas due to the convection through the night.

Monday through Friday: A cold front will push southeast toward the
GA waters into Monday night before shifting farther south and east
as high pressure builds from the northwest through mid week. The
high will then shift offshore later this week. This will lead to an
enhancement in winds/seas toward mid week as the gradient tightens
before conditions improve again late in the week.

&&

.TIDES/COASTAL FLOODING...
We`re still not convinced that tides will "officially" reach our
shallow coastal flooding criteria of 7.0 ft MLLW in downtown
Charleston with the high tide around 10-1030 pm this evening.
And provided the bulk of the rain has ended before then, we will
refrain from issuing an advisory at this time, as levels fall
about 0.1 ft MLLW shy. Most likely no coastal flooding for the
Ft. Pulaski/Savannah area as levels there rise to around 9.0 ft
MLLW.

The evening high tides will continue to be elevated through at
least Monday due to lingering astronomical influences. The
total departures will be driven by the position of the cold
front and the resulting winds that are either parallel to the
coast or onshore. Coastal Flood Advisories are still not out of
the question for the coastal areas from Charleston County to
Beaufort County.

&&

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

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...



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