Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 280357
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1057 PM EST Mon Feb 27 2017

.SYNOPSIS...
High pressure will push off the eastern seaboard today, with a weak
coastal trough to develop nearby tonight. High pressure will remain
over the Atlantic through early Wednesday. A cold front will move
through Wednesday night into Thursday, followed by more high
pressure for the end of the week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
As of 1055 PM: Isolated TSRA have developed over portions of SE
GA, TSRA continue off the GA coast. I will update the PoPs and
weather to reflect the latest observations. Overall, I think the
trends in the current forecast appear on track.

As of 925 PM: Cluster of strong to severe thunderstorms located
on AMZ374. These storms are likely responding CAPEs around 1000
J/kg near the western wall of the gulf stream and a stationary
boundary. These storm will continue to track to the NE. Inland,
light showers were sliding east over the coastal plain. I will
update the forecast to increase PoPs, especially over AMZ374.

As of 630 PM: IR satellite loop and lightning detection
indicated clusters of showers and thunderstorms were developing
across southern GA. The convection was developing in the
vicinity of a frontal wave. Based on the satellite and radar
trends, I expect that this convection will continue as it tracks
east this evening toward the mouth of the Savannah River. The
passage of the showers should make the development of fog more
likely during the pre-dawn hours. I will update the forecast to
adjust PoP placement and timing, I will also increase mention of
patchy fog.

As of 550 PM: KCLX has detected a fairly rapid increase in
shower coverage over the past hour. The coverage was the
greatest over the coastal area between the Edisto and the
Savannah Rivers. I will increase the PoPs to CHC across the area
of greatest coverage, elsewhere, I will increase to Shack.
Mesoscale analysis indicated very low values of SBCAPE, I will
keep the mention as SHRAs, an isolated TSRA is possible over the
outer GA waters.

Previous Discussion:
Mid level perturbations will traverse the area, allowing for
the development of a subtle coastal trough in close proximity to
the area. Isentropic ascent and moisture flux will combine with
upper diffluence/divergence to generate showers, so chance
POPs are forecasted. There looks to be three potential
mechanisms for how the showers gets going. First is the nearby
Atlantic trough, the second is the energy aloft, and finally
even the possibility that sea breeze induced convection from the
Gulf of Mexico will ride in from the southwest. There is some
elevated instability, so isolated thunder can`t be ruled out,
mainly near the immediate coast. Considerable clouds and warm
air advection will allow temperatures to remain mild. Expect
lows around 60 degrees.

Fog will become a concern after the precipitation ends late
tonight. This will be due to the wet grounds, the lack of winds,
and favorable condensation pressure deficits. If there is enough
build-down of stratus involved in the mix, then coverage might
be more than just patchy, and dense fog may also be an issue.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday through Wednesday Afternoon: The area will remain along the
western edge of Atlantic high pressure at the sfc and along the
northern edge of a large mid/upper lvl ridge of high pressure
centered over the Caribbean. The pattern will result in increasingly
unstable conditions as a southerly flow advects moisture and warm
air north into the area well in advance of a cold front approaching
from the west Wednesday night. Tuesday morning could start off with
some fog eroding as an inversion breaks early, but a few showers
and/or thunderstorm will be possible Tuesday afternoon, mainly for
inland areas where temps peak in the lower 80s. Record-breaking
temps will be possible Wednesday with afternoon temps approaching
the low/mid 80s away from the coast. A few showers/thunderstorms
will also be possible over inland areas into Wednesday evening, well
ahead of the cold front making way toward the Eastern seaboard late.

Wednesday Night through early Thursday: A strong cold front will
push through the region with showers and/or thunderstorms over much
of the area before daybreak Thursday. Although not climatologically
favorable for severe weather, there remains a low chance of some
thunderstorms becoming strong or perhaps severe near/along the
passing front. At this time, the greatest threat of severe weather
looks to be over inland areas in the form of damaging winds
associated with a weakening line of thunderstorms. Should the cold
front arrive earlier than anticipated, the chances of severe weather
will increase.

Thursday: Dry high pressure will build over the region behind a cold
front shifting offshore. We could see a few showers linger into late
morning hours behind the front, but conditions will significantly
improve by the afternoon. Temps will be noticeably cooler than the
previous day within a north/northeast sfc flow. In general, temps
should peak in the mid 60s Thursday afternoon.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Cool and dry surface high pressure will build into the area late
week and then slide into the Atlantic by Monday. Lack of moisture or
any significant forcing will allow for a precip-free forecast.
Temperatures will be near normal early in the period, then slowly
warm early next week as southerly flow develops on the backside of
the high.

&&

.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
As of 630 PM: IR satellite loop and lightning detection
indicated clusters of showers and thunderstorms were developing
across southern GA. The convection was developing in the
vicinity of a frontal wave. Based on the satellite and radar
trends, I expect that this convection will continue as it tracks
east this evening toward the mouth of the Savannah River. I
will TEMPO 5SM SHRA between 3z-7z at KSAV and 7Z-11Z at KCHS.
The passage of the showers should make the development of fog
more likely during the pre-dawn hours. Fog should dissipate by
mid- morning, leaving steady south winds and slowly decreasing
sky cover through the rest of Tuesday.

Extended Aviation Outlook: Flight restrictions possible in early
morning fog/stratus Wednesday. A cold front will move through early
Thursday with brief restrictions possible in low clouds and
showers/thunderstorms.

&&

.MARINE...
Tonight: There is enough of a weakness in the ridging across
the maritime community, allowing for a subtle trough to develop
over or near the area. The flow slowly veers to the SE at no
more than 10 to 15 kt. Additionally, there is enough
instability to have a slight chance of thunderstorms. Seas will
range from 2-4 ft.

Tuesday through Saturday: South/southwest flow will persist through
midweek as the coastal waters remain along the western edge of
Atlantic high pressure. In general, wind speeds of 10-15 kt on
Tuesday will increase 15-20 kt early Wednesday. There is a chance of
Small Craft Advisory level conditions Wednesday afternoon into early
Thursday, mainly for waters off the Charleston County coast and
offshore Georgia waters as a cold front pushes through the area
Wednesday night. A Small Craft Advisory could also be needed over
the Charleston Harbor Wednesday afternoon, mainly due to strong
winds over land drifting over waters. Expect conditions to improve
over all waters Thursday morning with winds turning to the
north/northeast behind the front shifting well offshore. High
pressure will then prevail over the waters late week with a brief
uptick of wind speeds Saturday morning.

Sea fog: A warm/moist southerly flow moving over cooler shelf waters
could result in patchy sea fog late Tuesday into Wednesday before a
cold front sweeps over the region Wednesday night.

&&

.CLIMATE...
Record high temperatures for March 1
CHS: 82 degrees last set in 1997
CXM: 79 degrees set in 1918
SAV: 86 degrees set in 1918

Record high minimum temperatures for March 1
CHS: 61 degrees set in 2012
CXM: 63 degrees set in 2012
SAV: 65 degrees last set in 2012

&&

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

&&

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



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