Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 220449
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1249 AM EDT Mon Jul 22 2019

.SYNOPSIS...
The area will remain between an inland trough and Atlantic high
pressure through Tuesday. A cold front will move through the
region Tuesday night, then stall off the coast, perhaps
lingering into the weekend.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Convection has ended for the night, and under clear or partly
cloudy skies temps will drop only another 2-4F through daybreak.
There are no fog concerns, and while most places will experience
SW winds less than 5 or 10 mph, winds over coastal sections of
SC remain somewhat elevated and as high as 15 or 20 mph.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/...
Monday: The mid-levels in the morning will consist of high
pressure in the western Atlantic and troughing stretching from
the Great Lakes region southwards into the TN Valley. As time
progresses, the high will get pushed away by the trough, which
will strengthen/amplify along the Eastern third of the country.
At the surface, our area will remain between an inland trough
and Atlantic high pressure. Moisture is forecasted to increase,
with PWATs starting ~1.75" in the morning, then exceeding 2"
late at night". The general thinking is the morning hours should
be dry, with convection firing up along the sea breeze in the
afternoon. Remnant convection could persist inland into the
evening, followed by additional convection developing over/along
the coast during the overnight hours. We tried to show this the
best that we can with the hourly POPs, but in simple terms,
expect chance POPs. Temperatures should remain a few degrees
above normal during both the day and at night.

Tuesday: The mid-levels will consist of a persistently strong
trough along the Eastern third of the country. In fact, NEAFS
shows the 500 mb anomaly 2-3 standard deviations below normal.
At the surface, our area will remain between an inland trough
and Atlantic high pressure early. The high will get pushed away
by a cold front, which will approach from the west and northwest
during the day. The front is expected to move through the
region during the evening hours, then stall just off our coast
overnight. A deep plume of moisture is expected with the trough,
with PWATs perhaps reaching 2.25". This is above normal per SPC
climatology. Additionally, NAEFS has above normal PWATs and
Integrated WV Transport values just to our north and it`s
perfectly reasonable these values will creep into our area with
time. The end result will be increasing showers during the day
followed by widespread showers during the evening and overnight
hours. Despite good lift from the front and plenty of moisture,
instability is somewhat tame. The GFS shows Showalter values
barely negative and MLCAPEs struggling to reach 1,000 J/kg. Even
the shear and DCAPEs with the front aren`t very impressive. We
backed off on the thunderstorm threat, lowering it to the chance
category. The risk of widespread severe storms is very low. The
rainfall will be the biggest impact, with some locations easily
exceeding 1". Temperatures should be near normal. Though, it`s
possible our highs may need to be lowered several degrees if the
sky cover is thicker than expected and the precipitation starts
sooner than expected.

Wednesday: The aforementioned mid-level trough persists in
place while the front stalls off our coast. A deep plume of
moisture will continue to brush along the coast with PWATs
exceeding 2". Given the good model agreement, we have likely to
categorical POPs over a good chunk of our area during the day.
Similar to Tuesday, the severe thunderstorm threat will be low.
Given the abundant cloud cover and precipitation, temperatures
will be below normal. It`s not out of the question some spots
may have a hard time reaching the 80 degree mark. But we`re not
ready to go that cool yet.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Slightly improved model agreement today that the front will
hang up offshore around the Gulf Stream Thursday and Friday. A
broad upper trough will linger over the region with a wedge-like
surface pattern and multiple waves of low pressure riding along
the stalled front offshore. This pattern appears to be wetter
for South GA with higher progged PWATs and a moisture low-level
feed of Atlantic air. Our POP gradients from 50-60 percent GA to
40 percent SC may not be tight enough but we have moderate
confidence in at least the gradient. Next weekend, model
uncertainty at this point and we ran with mainly climo POPs.
Temps are expected to run a bit below climo through late week,
perhaps warming a bit next weekend.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
VFR conditions are expected at both CHS and SAV terminals
through 06Z Tuesday. Isolated to scattered SHRA/TSRA will
develop from the sea breeze Monday afternoon and evening.
Should any direct impacts occur, then temporary flight
restrictions can occur from 19Z to 01Z, mainly at KSAV. For now
those chances are too minimal to include with the latest TAF
set.

Extended Aviation Outlook: Flight restrictions are expected as
a cold front approaches the region on Tuesday, moving through
Tuesday night, then stalling off the coast and maybe lingering
into at least Friday.

&&

.MARINE...
Rest of tonight: The coastal waters will remain situated
between high pressure across the western Atlantic and a trough
of low pressure inland. The pattern will result in a fair
pressure gradient across the local waters with SW winds topping
out in the 15-20 kt range for much of the night, including in
the CHS Harbor.While some occasional gusts near 25 kt will occur,
no advisory is necessary. Wind speeds should slowly decrease to
the 10-15 kt range late tonight into daybreak hours. Seas will
range between 2-3 ft.

Extended Marine: The coastal waters will remain between an
inland trough and Atlantic high pressure Monday and Tuesday.
Winds should be from the S to SW at that time, with higher gusts
in the afternoon/evening. A cold front will move through the
region Tuesday night, which will allow winds to ease and turn in
direction. The front is forecasted to stall off the coast and
linger into at least the weekend. Otherwise, Small Craft
Advisory criteria is not expected to be reached.

&&

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

&&

$$
NEAR TERM...
SHORT TERM...MS
LONG TERM...
AVIATION...
MARINE...


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