Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 181944
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
344 PM EDT Wed Jul 18 2018

.SYNOPSIS...
A cold front will approach the region from the north tonight
and will stall over or close our area Thursday and Thursday
night. The front will then slowly lift north as a warm front
Friday. A trough of low pressure will then persist into the
middle of next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Convection continues to increase in coverage, but overall
organization seems to be lacking. The better organized
convection is located just north of the area ahead of a slow
moving, weak cold front. More organized convection is still
shown by models to sink into at least the northern 1/3 of our
area toward evening. Boundary collisions along with ample CAPE
and DCAPE could result in isolated strong to severe storms. The
main impact from any stronger storms will be strong gusty winds.
Will continue with likely PoPs through at least early evening.

Temperatures have ticked up another degree or so since the last
discussion, with highs in the lower 90s most areas. These
temperatures combined with dew point temperatures in the mid to
even upper 70s is resulting max heat indices of 104-108 through
the rest of the afternoon, especially closer to the coast.

Still expect convection to pulse down during the evening, but
will keep chance PoPs for now. PoPs will likely need to be lowered
on later updates once convective trends become evident.

Low temperatures tonight will again be warm, in the mid to even
upper 70s most areas.

Patchy late night, shallow fog is possible late tonight in areas
that received rain. However, probabilities/coverage are too low
to mention in the forecast at this time.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Thursday through Friday: A cold front will stall over or close to
the region, and a deep-layered trough will reside over the region.
Pooling of rich moisture featuring PWATs well over 2 inches will
translate to an active period with numerous/widespread showers/
thunderstorms. maximum PoPs are capped at likely, with greatest
coverage from late morning into early evening both days. However,
locally greater PoPs will eventually be required, especially within
near term forecast updates. Also, convection could persist through
Thursday night without the usual significant/diurnal decrease in
coverage. The primary concern focuses on the potential for locally
excessive rainfall. The threat for severe weather/locally damaging
wind gusts should remain low. Clouds/precipitation should hold
max temperatures in the 80s, below normal for mid-July.

Saturday: Models agree that somewhat drier air will wrap around the
deep longwave upper trough over the eastern CONUS and into our
region. This should result in somewhat reduced coverage of diurnal
convection as compared with Thursday/Friday, and temperatures should
respond by recovering into the more typical lower 90s away from the
coast. warmer temperatures could produce stronger instability as
compared with the next couple of days, perhaps raising the threat
for a few pulse severe thunderstorms with brief/isolated damaging
wind gusts.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The models are in good agreement showing a strong trough over the
East Coast Saturday night through Monday, with it weakening on
Tuesday. However, they don`t agree as much with the surface pattern.
The models hint at a trough inland Saturday night into Sunday.
Another cold front will slowly approach from the northwest Sunday
into Monday. Then, they disagree over whether the front makes it to
our area or stays to the north. Regardless, the end result will be a
rainy weather pattern.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Rest of This afternoon: Convection continues to increase in
coverage. There is still a small potential for isolated strong
storms, especially closer to KSAV, which could produce wind
gusts of 30-40 knots. Still think convection will decrease
through the night, resulting in more isolated to scattered
convection.

Extended Aviation Outlook: Most of the time VFR conditions will
prevail. However, episodes of flight restrictions are likely in
convection, and low ceilings could occur even outside any
showers/thunderstorms during the late night/early morning hours.

&&

.MARINE...
No significant changes were made to the forecast through tonight.
Still expect a weak cold front to move toward the waters this
evening, likely stalling over/near the waters later tonight.
Scattered to numerous showers and thunderstorms expected later
this afternoon and into tonight. Stronger wind gusts will be
possible with some storms. Outside of any storms, winds are
expected to be 15 knots or less and seas 4 feet or less through
tonight.

Thursday through Monday: Thunderstorms will produce locally
hazardous conditions through the period. A cold front will stall
over the waters Thursday and Thursday night, pushing winds into the
east/southeast at 15 kt or less. Then, the boundary will lift north
as a warm front Friday, and winds will turn into the southwest and
could increase into the 15-20 knot range at times through early next
week. Seas only 1-3 feet through Friday will build to 3-5 feet,
highest beyond 20 nm, this weekend into early next week.

&&

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

&&

$$
NEAR TERM...RFM
SHORT TERM...SPR
LONG TERM...MS
AVIATION...MS/NED
MARINE...MS/NED



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