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000
FXUS62 KCHS 132045
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
345 PM EST Fri Dec 13 2019

.SYNOPSIS...
An area of low pressure will track across the area tonight.
High pressure should then build over the region Saturday and
persist into early next week. A cold front will shift across
the area Tuesday, followed by high pressure into late next
week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
The cold air damming regime has held strong today despite all
model data suggesting it would erode by mid afternoon. This is a
very common model weakness for this area. The surface low that
has been developing along the coast has remained over the Gulf
Stream as it tracks northeast with the cyclonic flow further
entrenching the high pressure wedge over land. The main upper
shortwave will gradually push northeast of the area through
early this evening. Meanwhile, as the surface low moves toward
the NC/SC border, the best isentropic ascent on its NW periphery
will shift north of the area. Much of the precipitation should
clear out from south to north through mid evening due to NVA in
the wake of the shortwave.

Late tonight a strong upper shortwave and the surface cold front
will sweep through the area. Strong forcing for ascent is
anticipated, especially given another round of strong upper jet
divergence coincident with the PVA associated with the
shortwave. A few hours of moderate to heavy showers are expected
to sweep through late tonight. Isolated thunderstorms are also
possible, mainly over the eastern half of the area where a bit
more elevated instability will exist.

Temperatures will rise little during the remainder of the
afternoon through tonight. The cool northeast flow is likely to
continue until daybreak Saturday when the cold front sweeps
through.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Mid-level troughing over the Southeast U.S. Saturday morning will
shift over the Northeast U.S. by Saturday night, causing semi-zonal
flow over our area. This flow will continue on Sunday. Sunday night
into Monday broad high pressure will be building over the Bahamas
while troughing amplifies over the Central U.S., leading to
southwest flow over our area. At the surface, low pressure and it`s
attached from will be moving away from our area Saturday morning
while high pressure moves in from the west. The high is forecasted
to prevail over the Southeast U.S. late Saturday into Sunday, then
shift offshore Sunday night. As the high continues to move further
offshore on Monday, a front will approach from the distant west.
Though, it`s not expected to reach our area in the short term. The
only precipitation we are expecting in the short term is early
Saturday morning, as the aforementioned low/front moves away. Some
remnant showers, especially along the coast, should bring little, if
any, measurable QPF. Then, the high will become the dominant driver
of the forecast for the rest of the short term. Subsidence and dry
air associated with the high will bring our area dry conditions into
Monday. High temperatures should generally be in the 60s Saturday
and Sunday. Highs rise well into the 70s on Monday as winds turn to
the south/southwest, ushering warmer air into the region.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
The area will become warm-sectored Monday night into Tuesday ahead
of a cold front expected to shift across the region Tuesday
afternoon afternoon/evening. Temps will be the warmest of the week
on Tuesday, peaking in the mid 70s across several areas. Sfc heating
should also be sufficient to produce some instability along/near
fropa, suggesting a few thunderstorms embedded in numerous showers
until the front reaches the coast. Dry and cooler high pressure will
then build across the area Tuesday night through late week. Temps
will be some 15-20 degrees cooler following the front with highs
generally peaking in the mid/upper 50s and overnight lows in the
low/mid 30s away from the coast. A few showers could return next
weekend as a coastal trough takes form along the Southeast
Coast.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
IFR, as well as possible LIFR conditions are expected to prevail
through 23Z as a low pressure system continues to move through the
area and lift northeast by 00Z. Until then, showers are expected to
linger around both terminals, with heavier rain at times. By 00Z,
showers are expected to lessen, with VCSH to prevail at both TAF
sites. Fog and low clouds will support IFR to LIFR conditions at
both terminals. Around 06Z, a cold front will start to move through
the area, bringing more rain to both terminals and the continuation
of lower ceilings and visibilities. By daybreak, showers are no
longer expected with vsbys and ceilings improving with the passing
of the cold front. By 15Z, VFR conditions are expected.

Extended Aviation Outlook: VFR through Monday. Flight restrictions
are possible at both terminals Tuesday due to showers/thunderstorms
along a passing cold front.

&&

.MARINE...
Winds may eventually become south later tonight as the coastal
trough shifts inland. However, speeds will be at or below 15 kt.
Nevertheless, seas will be at or above 6 ft over the Charleston
nearshore and GA offshore through the night, thus necessitating
the continuation of Small Craft Advisories in those two zones.

An area of low pressure and its associated front will be moving
away from the coastal waters Saturday morning while high
pressure approaches from the west. The interaction between these
two features will lead to elevated winds for most of Saturday.
The worst conditions appear to be Saturday late afternoon. Small
Craft Advisories will be ongoing for most of the waters, except
AMZ354 and Charleston Harbor where wind gusts should remain
just below 25 kt. The winds are expected to ease late Saturday
evening through the overnight hours as the high becomes more
dominant across our area. All of the advisories should expire
across the waters by daybreak Sunday. The high is forecasted to
persist into early next week. A cold front will shift across all
coastal waters Tuesday, producing another round of cold air
advection across the region and the potential for Small Craft
Advisories Tuesday night into early Wednesday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 10 AM to 9 PM EST Saturday for
     AMZ352.
     Small Craft Advisory until 5 AM EST Sunday for AMZ374.
     Small Craft Advisory until midnight EST Saturday night for
     AMZ350.

&&

$$
NEAR TERM...JRL
SHORT TERM...MS
LONG TERM...DPB
AVIATION...MS/RAD
MARINE...JRL/MS