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000
FXUS62 KCHS 122009
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
409 PM EDT Fri Apr 12 2024

.SYNOPSIS...
High pressure will gradually build across the region into the
weekend, and persisting through much next week. A cold front
might impact the area late in the week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Satellite water vapor indicated a broad longwave trough across the
eastern U.S., with a shortwave passing over the southern
Appalachians this afternoon. The disturbance is expected to pass
east, tracking over middle and eastern NC late this afternoon and
evening. This feature may support a weak field of cumulus across the
CHS Tri-county late this afternoon, dissipating around sunset. At the
sfc, a sfc trough will sweep across the forecast area late this
afternoon and evening. In the wake of the trough, the combination of
weak CAA and a pinched pressure gradient should result in wind gusts
remaining past sunset. Conditions tonight will feature clear sky and
steady west winds. Minimum temperatures are forecast to range from
the mid 40s inland to the low to mid 50s along the coast.

Lake Winds: Strong and gusty winds will continue across Lake
Moultrie, as well as along the western lakeshore. Frequent gusts
into the 25-30 knot range are expected and a Lake Wind Advisory has
been extended until midnight tonight.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Saturday: The upper trough in the Atlantic will pull further away,
allowing for ridging and it`s associated climbing heights to
approach from the west. Surface high pressure initially over the
northern Gulf of Mexico coast will expand east, while a trough
lingers upstream from the local area through the day. Downslope
flow, full insolation and 850 mb temperatures about 2C greater than
on Friday suggests an even warmer day. This results in afternoon
highs of 73-77F degrees. There is still a modest gradient in place,
and that along with deep mixing will produce some gusty breezes
throughout, peaking at 20 mph or a little higher.

Saturday night: High pressure is the main feature, as the trough
dissipates or becomes less defined. Winds quickly decouple by
sunset, and with clear skies and within a very dry air mass,
excellent radiational cooling will commence. We leaned toward the
cooler side of guidance, supporting lows generally in the upper 40s
and lower 50s. However, some middle 40s are likely in normally
colder rural sections of Berkeley, Dorchester and Colleton County,
with the Charleston-North Charleston and Savannah urban sections,
and the barrier islands in the middle 50s.

Sunday through Monday: An intense upper low digs through southeast
Canada, with another deep low moving through the Southwest U.S. In
between there is ridging across much of the central states. The
local vicinity lies within a fairly dry west-northwest flow, with
subtle impulses to move through at times. These features won`t be
able to generate anything more than some clouds, especially with
subsidence associated with Bermuda high pressure eventually
establishing itself. This is the beginning of even warmer weather,
with higher 850 mb temperatures and heights, along with expanding
low level thicknesses. We currently looking at highs well into the
80s, except for coastal sections where the afternoon sea breeze
holds temperatures down into the 70s if not cooler. Much warmer
Sunday night than the previous night, with winds never fully
decoupling in most communities and dew points much higher within a
south to southwest synoptic flow.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Ridging aloft will prevail through the first half of the week,
before it breaks down late in the period. This is in response to a
fast moving short wave that is progged to move across the southern
tier of the country. However, since we`re mainly still under the
influence of Atlantic high pressure and the flow aloft in westerly,
and moisture is still rather limited through at least Wednesday,
rain chances are slim to none. Maybe by late week as a cold front
approaches we might finally get some showers into the local area.
Temperatures stay far above climo through most, if not all the week
thanks to 850 mb temperatures near or above the 90th percentile.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
VFR conditions will prevail at KCHS, KJZI, and KSAV through 18z
Saturday. West winds will continue to gusts between 25-30 kts
until mid-evening. The rest of the night should feature west
winds around 10 kts. Gusty northwest winds are forecast to
redevelop across the terminals by 14Z Saturday.

Extended Aviation Outlook: VFR. Gusts will reach near 20 kt at
times Saturday afternoon.

&&

.MARINE...
Tonight: High pressure will continue to build over the marine zones
tonight. A sfc trough is timed to sweep across the marine zones this
evening, resulting in a pinched pressure gradient and CAA late this
evening into the late night hours. West winds may continue to gust
to around 25 across the Charleston Harbor into this evening. A Small
Craft Advisory is in effect until 10 PM. Outside the harbor, winds
across the nearshore waters of SC/GA will gusts between 25-30 kts
through most of the night. Seas will remain between 3-6 ft through
most of the night. Small Craft Advisories will remain in effect for
the majority of tonight. The outer GA waters should see gusts of 25
to 30 kts continue into Saturday morning.

Saturday: The remaining Small Craft Advisories will come down during
the morning, as the gradient finally starts to slowly slacken, and
high pressure edges east of the northern Gulf of Mexico coast. W
winds will drop to 15 kt or less, except a little higher in
Charleston Harbor. Offshore flow will allow for seas to fall to less
than 3 or 4 feet in the afternoon.

Saturday night through Wednesday night: Excellent boating weather
under the control of high pressure, resulting in winds and seas far
below any advisory thresholds. One possible exception to that would
be Charleston Harbor, with afternoon sea breeze influences having to
be carefully monitored due to the potential for some gusts maybe as
high as near 25 kt (the requirement for a Small Craft Advisory).

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Lake Wind Advisory until midnight EDT tonight for SCZ045.
MARINE...Small Craft Advisory until 10 PM EDT this evening for AMZ330.
     Small Craft Advisory until 8 AM EDT Saturday for AMZ350.
     Small Craft Advisory until 6 AM EDT Saturday for AMZ352-354.
     Small Craft Advisory until 11 AM EDT Saturday for AMZ374.

&&

$$

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