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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 241715

Area Forecast Discussion
National Weather Service Charleston SC
115 PM EDT Wed Apr 24 2019

High pressure will prevail through Thursday. Low pressure and a
cold front are forecasted to bring unsettled weather on Friday.
High pressure returns for the weekend and prevails through the
first half of next week. 


This Afternoon: Sfc high pressure will remain centered over the 
western Atlantic while a low amplitude ridge of high pressure 
persists aloft. The pattern favors warm and dry conditions within a 
west-southwest wind between the sfc high offshore and a sfc trough 
of low pressure well inland. Overall, high temps will be dependent 
on the thickness or cirrus aloft and the timing of a seabreeze 
circulation gradually shifting inland late this afternoon. At this 
time, abundant sunshine and 1000-850mb thickness levels support
temps peaking in the upper 80s away from the coast. 

Tonight: Overall, very little change to the setup through the 
overnight with high pressure to the east driving southwesterly flow 
across the forecast area. Expect a dry and mild night with lows 
falling to around 60 away from the coast.


Thursday: The mid-levels will consist of weak ridging over the 
Southeast during the day. The ridge will get pushed offshore in 
the evening and overnight as a trough starts to move over the 
Southeast by daybreak Friday. At the surface, high pressure will
be far offshore during the day and moving away. Meanwhile, a 
storm system and its cold front initially over the Southern MS 
Valley will continue it's eastward movement, making its way into
the Southeast by daybreak. The outer periphery of the high will
give our area dry weather during the day and into the first 
half of the night. After midnight, showers associated with the 
storm system should start making their way into our far inland 
counties, bringing measurable rainfall. Southwest winds and 
partly sunny skies ahead of the storm system will allow daytime 
temperatures to make another run for the 90 degree mark in many 
locations, just a few degrees short of the records. Though, it's
possible highs may be limited if clouds increase faster than 
expected. Overnight lows will be very mild, well into the 60s.

Friday: The mid-levels in the morning will consist of a trough 
over the Southeast. A decent lob of vorticity will be embedded 
within this trough as it moves eastward during the day, then 
moving offshore during the evening and overnight. At the 
surface, a storm system and its cold front will slowly cross 
through the Southeast during the day, moving offshore during the
evening and overnight. Models show a better plume of moisture 
ahead of the front with PWATs approaching 1.6" in the morning, 2
standard deviations above normal per NAEFS. Models are in 
fairly good agreement showing widespread showers across our area
during the day. Though, they have some minor differences on how
fast the showers move out in the evening. For now, we have 
likely POPs during the day. These may need to get raised more. 
Storm total QPF appears to be ~0.25". There is some instability 
ahead of the front, but it's far from impressive. Hence, we're 
going with a chance of thunderstorms in the afternoon, but 
nothing severe. Highs will be "cooler" barely making it to 80 
degrees. With both showers and skies clearing overnight, lows 
will drop into the 50s.

Saturday: Mid-level troughing offshore in the morning will move
away, allowing semi-zonal flow to prevail over our area. At the
surface, broad high pressure will build over the Southeast. 
Expect dry conditions with mostly sunny skies. High temperatures
will be near normal.


Models are in fairly good agreement showing high pressure over 
or nearby our area this weekend and continuing through the first
half of next week. There remain hints from some of the models 
at sea breeze convection developing at times early next week. 
But with the aforementioned high we're either keeping the 
forecast dry or daytime POPs limited to slight chance at most. 
Highs will be near normal.


VFR conditions will prevail at both CHS and SAV terminals through 
18Z Thursday. Southwest winds could gust up to 15-20 kt with an
afternoon seabreeze at both terminals. 

Extended Aviation Outlook: Low pressure and a cold front are 
expected to bring flight restrictions on Friday. VFR returns 
Saturday and beyond.


This Afternoon and Tonight: Southwest flow will prevail across the 
local waters as the region remains between high pressure over the 
western Atlantic and a trough of low pressure well inland. Winds 
this afternoon will likely gust into the 15-20 kt range for 
most of the waters as a strong afternoon seabreeze develops. 
Speeds will decrease overnight, falling more into the 10-15 kt 
range. Seas will be in the 2-4 ft range through the period.

Extended Marine: High pressure offshore Thursday will move 
further away from the coast. Though, the main driver in winds 
that afternoon will be the seabreeze circulation. Friday a storm
system and its associated cold front will move through the 
waters, probably during the evening. Winds and seas are expected
to increase with the front. Gusts could approach Small Craft 
Advisory levels, especially in the Charleston Harbor. But for 
now we're forecasting them to be just below 25 kt. High pressure
returns for the weekend and prevails through early next week, 
bringing tranquil marine conditions.