Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 231150

Area Forecast Discussion
National Weather Service Charleston SC
650 AM EST Sat Feb 23 2019

A high pressure wedge across the area today will give way to a
warm front tonight. A cold front will pass quickly through
Sunday and is followed by high pressure into the middle of next
week. Low pressure may pass nearby late in the week.


As of 640 AM: Ongoing 12Z sounding indicate a strong inversion
between the sfc to 2.5 kft, with a 10 degree temp difference.
Moisture trapped under the inversion will likely support low
cloud cover through the day. Rounds of isentropic lift is
expected to support drizzle to isolate showers this morning. I
will update the forecast to extend the mention of drizzle.
Temperature trends will also be updated with the latest

As of 420 AM: The GOES-East Night Fog product clearly showed
the stratus associated with the backdoor cold front advancing SW
across the FL/GA line. Near term guidance indicates that cold
air damming will remain entrenched across the Carolinas and GA
today. NAM12 indicates that weak isentropic lift will continue
between 295-305K this morning, supporting widespread low clouds
and patches of light fog. However, steady NE winds should result
in dewpoints to lower an addition 1-2 degrees around dawn,
resulting in land fog to dissipate at sunrise. Rounds of shallow
isentropic lift will pass over the CWA today, supporting
isolated showers or patches of drizzle, high lighted with SCHC
PoPs. The widespread clouds, periods of light rain, and late
morning wind shift from the ESE will make the max temperature
forecast challenging. Based on the latest MOS, I will forecast
temperatures to range from the mid 60s across the CHS Tri-
county to the mid 70s along the Altamaha River.

Tonight: A warm front is timed to lift north across the forecast
area shortly after midnight. Steady south winds will develop in the
wake of the warm front.Isolated to scattered light showers should
develop as the front lifts across the region, highlighted with SCHC
to CHC PoPs. Low temperatures should be set during the late evening,
followed by steady to slowly warming temps through the rest of the
night. Low temperatures are forecast to range from around 60 across
the SC Lowcountry to the mid 60s across SE GA. Sfc dewpoints in the
low 60s will flow over the mid-50s shelf waters and will result in
widespread sea fog along the coast. Beginning along the GA coast
early this evening and lifting to Charleston County during the pre-
dawn hours.


Sunday: A fast moving cold front is still on track to push rapidly
through the forecast area, as it reaches our northwest tier during
the morning and shifts offshore into the afternoon. A band of
showers will accompany the front with a sufficient feed of moisture
from out of the Gulf of Mexico and aided by the right rear quadrant
of the upper jet that moves by to the northwest and north. With Pwat
to climb as high as 1.8 to 1.9 inches, or about as great as it can
get in February, we are showing 70 PoP`s across the board. But the
day is certainly not a washout, as the fast progression to the
showers will lead to about an hour or so of rain at any given
location. QPF on average is no more than about 1/10 of an inch. The
risk for isolated t-storms is non-zero given a little instability
and CAPE, but this is not enough to warrant including in the
forecast. As H8 temps reach 13-14C, this supports max temps in the
upper 70s to around 80, except several degrees cooler near the
Atlantic. Winds will be gusty at times throughout the day, reaching
as high as 20-25 mph.

Sunday night: A modified Canadian air mass will build from the
Plains and southern Canada, with rapidly rising pressures in wake of
the front. Skies will clear and as cold advection ensues, temps by
Monday morning will be as much as 30-40F cooler than highs on

Monday through Tuesday: A zonal flow will dominate aloft, as surface
and low level high pressure overhead Monday slides into the Atlantic
during Tuesday. There is some return flow of moisture from off the
ocean Tuesday, but large scale subsidence and the lack of any
forcing suggests that it`ll remain rainfree through the period. H8
temps are near 5-7C both days, while H10-H8 thickness of 1330-1340
meters Monday climbs about 15-20 meters Tuesday. This supports max
temps 65-70F Monday and 67-71F Tuesday, with both days a little
cooler near the ocean.


Zonal flow in the mid and upper levels will prevail until late in
the week, when a short wave trough is currently forecast to
approach the region. At the surface there remain model differences,
and as such our confidence Wednesday through Friday is low. Due the
uncertainty we have leaned considerably toward the previous forecast
which shows no more than chance PoP`s through the period, while
temps will average above normal as the calendar changes from
February to March.


A strong low level inversion and broad weak forcing will
maintain IFR to LIFR ceilings across the terminals through the
12Z TAF period. Ceilings may improve to upper IFR to lower MVFR
during the heat of the afternoon, most likely at KSAV. Given a
nearly saturated BL and broad forcing, rounds of drizzle or mist
may pass over the terminals into the early daylight hours. A
warm front is expected to lift across the region tonight,
resulting in winds to shift from the SE. Ceilings should
gradually lower in the wake of the warm front, the potential for
fog will be greater during the pre-dawn hours Sunday.

Extended Aviation Outlook: Continued flight restriction tonight
until a warm front lifts through, and then a period of possible
flight restrictions associated with a band of showers with a cold
front late Sunday morning and early in the afternoon. The next
chance of any sub-VFR weather won`t be until the middle of next
week. Also, gusty SW and W winds will occur at times Sunday, peaking
around 20-25 kt at both terminals.


Today: Sfc high pressure will gradually weaken today. Northeast
winds will begin the day with gusts around 20 kts across the SC near
shore waters. By this afternoon, winds should shift from the ENE at
around 10 kts. Wave heights are forecast to range from 2 to 4 ft.
Sea fog is expected to linger across the nearshore GA waters through
much of today.

Tonight: A warm front is timed to lift north across the waters
during the evening hours, resulting in winds to shift from the
south. Sfc dewpoints are forecast to warm into the low 60s as shelf
water temps remain in the mid 50s. Conditions will be nearly optimal
for widespread dense sea fog across the near shore waters and the
Charleston Harbor tonight. Seas should range between 2 to 5 ft,
highest beyond 20 NM.

Sunday and Sunday night: A fast moving cold front will move into the
local waters early Sunday afternoon, and clears the marine area well
before nightfall. Although winds will be tempered somewhat by the
warm advection, given a 35-40 kt low level jet on both of the front,
and then good isallobaric pressure rises and cold advection behind
the front, Small Craft Advisories will likely be required for at
least parts of the area. Sea fog will still be a concern in the
morning, with dense fog already in place, before it clears out with
the cold front.

Monday through Thursday: High pressure will prevail through mid
week, with perhaps an area of low pressure nearby late in the week.
For the time being winds and seas look to stay beneath any advisory
thresholds, while there doesn`t appear to be any chance of sea fog
through the entire period.


The Charleston Harbor residual has increased slightly above .6
meters early this morning. The ongoing gusty NE winds should
maintain the residual through this mornings high tide, with .4
meters need to reach 7 ft MLLW. I will adjust the morning high tide
up to 7.1 ft MLLW and highlight with a Coastal Flood Advisory for
the SC coast from 14Z-17Z.

I will continue to monitor Fort Pulaski to see if the early
morning residual decreases.


Record Highs for February 24...
KCHS: 81/2017 and previous
KCXM: 81/1930 KSAV: 86/2012

Record High Mins for February 24...
KCHS: 60/1992 and previous
KCXM: 63/2018
KSAV: 64/1980


SC...Coastal Flood Advisory until noon EST today for SCZ048>050.


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