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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 182322
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
722 PM EDT Sun Apr 18 2021

.SYNOPSIS...
A stationary front will linger offshore and to the south early
this week. A cold front is expected to push through the region
on Wednesday, followed by dry high pressure through late week.
Low pressure and a more unsettled weather pattern could impact
the region next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Based on latest trends and the expectation that there is just
too much dry air in place with condensation pressure deficits
greater than 30 or 50 millibars, we trended even lower on the
coverage of showers tonight. For now we have no more than 20-30%
PoP roughly south of a line Skidaway Island to Midway to
Ludowici. Another mild night, with lows close to 5F above climo.

Previous discussion...
Zonal flow will prevail in the mid-levels this evening, with a
weak shortwave moving over the Appalachians towards daybreak
Monday. At the surface, a stationary front will be offshore and
stretching to our south. Likewise, models have the highest
PWATs and POPs in these locations. Similar to 24 hours ago, the
synoptic models tended to show higher QPF amounts inching into
our far southern and coastal counties overnight, while the CAMs
had much lower QPF amounts in these same locations and keep a
majority of our area dry. Given the CAMs performed better
yesterday into today and considering the pattern of drier
conditions winning, we leaned more towards the CAMs with this
package. Lows will generally be in the 50s for most locations
and the lower 60s at the beaches.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
A weak upper level short wave will be departing north of the area
for the first part of Monday, followed by generally zonal to west-
southwest upper flow.  Another weak upper short wave is expected to
move just southeast of the region on Tuesday. By Wednesday, a broad
upper trough is shown by models to cover the entire eastern and
southeastern portion of the country.

The overall dry pattern is expected to continue, with significant
rainfall not expected. The best chance for any rainfall still looks
to be Tuesday, as better deep layer moisture associated with a weak
upper level short wave impacts mainly the southeastern portion of
our CWA. Have mostly slight chance PoPs, reaching low end chance
PoPs over the extreme southeast portion of the area and Atlantic
Waters. Any precipitation chances are expected to end by Tuesday
evening. By Wednesday, as the broad upper trough moves into the
area, there models show that the associated surface cold front will
move through dry/no precipitation.

High temperatures are expected to be near to slightly above normal.
Mainly in the mid 70s to around 80. Slightly cooler in the mid to
upper 70s for Tuesday given more clouds and slight chance for
precipitation/showers. Lows around normal in the lower to mid 50s
most areas through Tuesday night. With afternoon surface dewpoints
relatively dry /in the 40s Monday, 50s Tuesday, and then 40s again
on Wednesday/ afternoon conditions will feel very pleasant.

Lake Winds: There are indications that winds will be strong
enough for a Lake Wind Advisory on Lake Moultrie given deep
mixing and a tight gradient ahead of and behind the next cold
front during mid week.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Models are in good agreement for late week showing cool and dry high
pressure prevailing. Unsettled weather is then expected over the
weekend as low pressure impacts the region. Positioning and details
are still a bit uncertain, but regardless, this system will bring
healthy rain chances to the local area. Temperatures through the
period will average below mid/late April climatology.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
VFR through 00Z Tuesday. Gusty W-NW winds Monday afternoon
through the early evening.

Extended Aviation Outlook: VFR conditions expected to prevail
through the week. Winds could get a bit gusty Wednesday as the
dry cold front moves through the area.

&&

.MARINE...
Tonight: A stationary front will be offshore and to our south,
leading to "gentle" to "moderate" SW breezes much of the night.
Land breeze circulations will allow for winds to veer more W
closer to daybreak. Seas will average 2 or 3 feet.

Monday and Tuesday: No highlights are expected with winds generally
15 knots or less and seas 2 to 3 feet.

Wednesday and Wednesday Night: Winds and seas are expected to
increase ahead of, and then behind the next cold front, which will
likely push through the waters later half of Wednesday. Models
indicate winds reaching marginal SCA levels, with seas possibly
reaching 5 to 6 feet beyond 20 NM offshore.

Thursday and Friday: Winds and seas expected to fall back below
highlight levels as high pressure builds over the waters.

&&

.FIRE WEATHER...
Minimum relative humidity values Monday afternoon are
expected to be 25-30% away from the immediate coast. Wind gusts
will be near 20 mph at times, and we will need to consider Fire
Danger Statement given the lack of rainfall the past several
weeks.

A combination of gusty winds, low relative humidity, and dry
fuels could produce hazardous fire conditions Wednesday
afternoon/early evening.

Very low relative humidity is expected to persist into Thursday
and Friday afternoons. Though, sustained winds may remain below
10 mph.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...ETM
AVIATION...
MARINE...
FIRE WEATHER...