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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 201426
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1026 AM EDT Sat Apr 20 2019

.SYNOPSIS...
A weak surface trough will prevail to the west through tonight.
High pressure is forecasted to dominate the weather Sunday
through Wednesday or Thursday. The next cold front may approach
late next week. 

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
An unusually strong deep layered cyclone centered over the 
Cumberland Plateau will slowly propagate away from the Southeast
U.S. later today as surface high pressure over the western Gulf
of Mexico expands to the east and northeast. The associated mid
and upper trough extends south into the northeast Gulf of
Mexico as it moves eastward. Steep mid level lapse rates and
cold mid levels where H5 temps are as low as -16 to -20C will
lift through this afternoon. This is already generating a few
light showers over Jenkins County as of late morning, while more
organized showers are situated just west of the Georgia 
interior counties. We anticipate that some of these will move 
into locations near and west of US-301, so we have added mention
of slight chance PoP there. Cloud cover will play a critical 
role in max temps this afternoon, so we have trimmed the far 
inland areas 1-2F where we will experience more cloud cover 
(70-90%), but left the coastal sections the same where cloud 
cover will be less (40-60F). We still might need to lower a few 
places from Allendale to Candler for max temps, as the HRRR and 
RAP show those places not hitting 60F.

Deep mixing will tap into modest low level 
winds to result in gusty southwest and west breezes as high as 
25-30 mph. 

Lake Winds: Although the sensor at Pinopolis will not be
sampling conditions on the lake that well today, given the
latest sounding data, both surface and aloft, and the fact that
we're already seeing wind gusts in the upper teens, we have
raised a Lake Wind Advisory for Lake Moultrie through 8 pm. The
strongest gusts will generally be over and near the shores of
the lake this afternoon and early evening.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
Tonight: Winds will gradually diminish tonight under clear
skies. While a full decoupling of the boundary layer does not
appear likely, decent radiational conditions are still expected
to dominate. Used the colder side of guidance to construct 
overnight lows with localized adjustments to take into account 
the normally colder locations such as the Francis Marion 
National Forest. Lows will range from the mid 40s inland to the 
lower-mid 50s at the beaches.

Sunday: The mid-levels will consist of a strong trough along the 
East Coast in the morning. The trough will weaken and lift to the 
northeast with time, allowing heights to rise over our area. At the 
surface, broad high pressure initially centered over FL will spread 
across the Southeast with time. A dry forecast with mostly sunny 
skies is on tap. Rising 850 mb temperatures and heights will lead to 
temperatures within a few degrees of normal for this time of year.

Monday: The mid-levels will consist of a trough over the 
Northeastern U.S. in the morning. As this trough continues to lift 
to the northeast with time, ridging will build over the Southeast. 
At the surface, high pressure will prevail over the Southeast. The 
dry weather and sunny skies continue. Temperatures are forecasted to 
rise a few degrees above normal, but remain cooler at the beaches 
due to the sea breeze.

Tuesday: The mid-levels will consist of riding over the Southeast 
that will continue to build with time. At the surface, the center of 
broad high pressure initially over the Southeast in the morning will 
start to trend offshore into the evening. Same story, different day. 
Dry weather and sunny skies. Thee only difference is temperatures 
are a few degrees warmer.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
High pressure will prevail along the Southeast Tuesday night into 
Wednesday, then shift further offshore Wednesday night into 
Thursday. The result will be dry conditions and above normal 
temperatures. By Thursday night and Friday a trough or cold front is 
expected to move over the region, bringing showers and cooler 
temperatures. Though, models differ on the strength, timing, and 
potential impacts. Hence, we went with a blend for the forecast.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
VFR. Gusty winds will linger at both KCHS and KSAV for much of
the period.

Extended Aviation Outlook: VFR.

&&

.MARINE...
This afternoon: Although conditions are much improved from
yesterday, both winds and seas will remain high enough to keep 
Small Craft Advisories in place for all marine zones. SW and W
winds will be as high as 20-25 kt, while seas will range from 
4-7 ft within 20 nm and 5-7 ft further out. earlier this morning
we received a report from the Charleston Pilot Boat from Buoy 6,
where there was a 2-3 foot wind wave from the west-southwest,
but a 4-6 foot swell from the east-southeast, creating hazardous
wave conditions.

Tonight: Seas will finally drop below advisory thresholds for
the Charleston and Georgia offshore legs this evening.
Otherwise, West winds will average 15-20 kt this evening, then 
diminish through the night. Seas will subside 3-5 ft Georgia
offshore and Charleston County legs with 1-4 f remaining legs by
daybreak Sunday.

Sunday through Wednesday: Broad high pressure initially 
centered over FL Sunday morning will spread across the Southeast
into Sunday evening. The high will prevail through Wednesday, 
then move offshore. The end result is tranquil marine 
conditions.

Rip Currents: Lingering swell energy coupled with breezy
conditions will support a moderate risk for rip currents all
beaches this afternoon.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Lake Wind Advisory until 8 PM EDT this evening for SCZ045.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for AMZ330-
     352.
     Small Craft Advisory until 11 PM EDT this evening for AMZ350-
     374.
     Small Craft Advisory until 1 PM EDT this afternoon for AMZ354.

&&

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