Area Forecast Discussion
Issued by NWS Charleston, SC

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268
FXUS62 KCHS 251218
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
718 AM EST Sun Feb 25 2018

.SYNOPSIS...
High pressure will weaken through tonight. A cold front will
slowly approach from the west on Monday, moving through the
region by Monday night. High pressure is forecasted to pass to
the north Tuesday, followed by a warm front moving northward
through our area Wednesday. Another cold front is expected to
cross Thursday, followed by high pressure.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Strong deep layered ridging will weaken only slightly
and flatten a bit maintaining plenty of mid level subsidence and
dry air aloft across the region for most of the day. Dry
weather will persist this morning with temps rapidly warming
into the upper 70s by late morning with a good bit of sunshine.
Through mid afternoon, we will see temps again likely topping
daily records at Charleston and Savannah. In fact we could
approach the warmest on record for February, especially at KSAV.
The mixed layer will deepen with the warming land mass,
allowing for S-SW breezes gusting to 20-25 mph at times. Late in
the afternoon, moisture will gradually deepen from the west and
various high resolution model output reflectivity prog shows a
narrow but broken band of shallow low-top convective rains
pushing out of the CSRA and midlands towards our inland zones
after mid afternoon. We expect little to no thunder with this
activity later today as mid levels are very unsupportive moving
into the ridge. We maintained some 20-30 POPs inland from U.S.
17 late day.

Tonight: Various interactions between mesoscale boundaries and
the remnant resultant sea breeze during the evening hours may
result in isolated to scattered showers on the fringe of the 1.5
inch PWATS across our western and northern zones. To the south
of I-16, any spotty showers will be harder to come by as upper
forcing and deeper moisture remain off the north. We trended
POPs in the middle of the road toward the ECMWF which was a
general compromise between the wetter GFS and drier GEM/NAM.
While the stalled front to our west awaits a developing surface
wave along the Gulf Coast region, we will see another moist and
mild night with light southwest flow. We considered adding some
patchy late night fog to the forecast but with a complex
mesoscale and uncertain cloud cover, we held off on the mention
but it may need to be included at some point. Lows will mainly
be in the 60-62 degree range.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
Monday: The mid/upper levels will consist of strong high pressure
over Southern FL and the Bahamas in the morning, shifting into the
southern Gulf of Mexico overnight. The result will be southwest
winds over our area in the morning, becoming westerly in zonal flow
overnight. At the surface, a cold front will be just to our west
during the day, crossing through in the evening or overnight. PWATs
will be ~1.5" ahead of the front, which is almost 3 standard
deviations above normal per NAEFS. POPs reflect the expected showers
during the day, diminishing overnight with frontal passage.
Measurable QPF is expected for the entire area. There is some
instability, so a slight chance of thunderstorms are forecasted in
the afternoon. Ahead of the front, temperatures will remain well
above normal.

Tuesday: The mid/upper levels will consist of zonal flow over the
Southeast. At the surface, a cold front will be over the coastal
waters in the morning, quickly departing. At the same time, high
pressure will be centered to the north over the Mid-Atlantic states.
The high will bring dry conditions. Thickness values still support
high temperatures above normal. Showers are possible overnight.

Wednesday: The coastal trough will merge with a developing warm
front, which will move northward through the area during the day.
Showers are expected as PWATs rise well above normal.
Temperatures will also be above normal.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
A warm front will move north Wednesday night. A cold front will
then approach from the west, moving through Thursday night.
High pressure will then follow.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
VFR conditions today. Deeper mixing and nearby sea breezes
should enhance surface winds this afternoon with SW 12-15 kt
speeds common with at least occasional gusts in the 20-25 kt
range. Deeper moisture this evening may result in some MVFR
cigs and perhaps some shower activity in the coastal corridor.
Later tonight, a slot of drier air in the boundary layer to
850 MB suggests we may see expanding MVFR/IFR cigs and maybe
some lowering vsbys, especially at KSAV. We have introduced
scattered clouds below 1 kft ft to trend and some light fog.

Extended Aviation Outlook: Flight restrictions are expected
with a slow moving cold front late Sunday night into early
Tuesday.

&&

.MARINE...
Through tonight: A cold front to the west will slow it`s
progression and become less defined with time, remaining
well inland from the waters. SW to S flow will continue
over the marine forecast area with a poor low-level mixing
environment over cooler shelf waters. We expect wind speeds
mainly 15 kt or less. It could become a bit gusty for a period
this afternoon along the intra-coastal waterways of Charleston
County in the vicinity of the resultant sea breeze boundary.
Patchy sea fog is possible tonight over the cooler shelf waters
with a decent formation regime in the evening, looking less
favorable nearing daybreak as low level wind fields increase
and veer more southwest.

Monday through Tuesday: The cold front will gradually advance
through the waters, passing to the south of the area late Monday
night, as continental high pressure from the north into Tuesday.
Cool advection, steady isallobaric pressure rises and modest
pinching will likely support Small Craft Advisories developing
Monday night and continuing into Tuesday. Some fog will persist in
advance of the front, more as stratus clouds behind the front.

Wednesday through Thursday: Surface high pressure slides into the
Atlantic and further offshore, allowing for a cold front to approach
the SE late in the period. Winds and seas will be beneath advisory
levels Wednesday, but a much stronger S-SW gradient will exist on
Thursday, and SCA`s could again be common.

&&

.CLIMATE...
Record high minimums for February 25:
KCHS: 62/1992
KSAV: 63/1992
KCXM: 61/2017

Record highs for February 25:
KCHS: 81/2017
KSAV: 82/1985

Record high minimums for February 26:
KCHS: 62/1939
KSAV: 63/1939
KCXM: 62/1957 and previous

Record highs for the month of February:
KCHS: 87/February 16, 1989
KSAV: 86/last set February 24, 2012
KCXM: 83/February 27, 1962

&&

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

&&

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



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