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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 192003

Area Forecast Discussion
National Weather Service Charleston SC
403 PM EDT Fri Apr 19 2019

A strong cold front will move offshore early tonight. Low
pressure over the Ohio Valley will prevail Saturday, followed
by high pressure Sunday through Wednesday or Thursday. The next
cold front may approach late next week. 


Update: The line has cleared the forecast area and the tornado
threat is over. Thus, the Tornado Watch has been canceled. Also,
canceled the Wind Advisory outside of Charleston County and
Tidal Berkeley. The best gradient winds have been disrupted by
the passing convection and while gusty winds will still occur
gusts should remain below advisory criteria. 


Tonight: Expect rapidly improving conditions as a strong cold
front pushes offshore. Lows will drop into the upper 40s inland
to the mid-upper 50s at the coast. 

Saturday: The mid-levels will consist of a unseasonable strong 
trough over the eastern half of the country in the morning with low 
pressure near the OH Valley. In fact, NAEFS shows 500 mb heights 
near the core of the trough about 4 standard deviations below normal 
for this time of year. As time progresses, the trough will shift to 
the east, with its southern extent beginning to move offshore by 
daybreak Sunday. Meanwhile, the low continues to meander near the OH 
Valley. At the surface, in the morning a strong cold front will be 
moving off the East Coast while low pressure is near the OH Valley. 
Weak troughing will extend from the low into the TN Valley. As time 
progresses, the cold front will continue to shift further offshore 
while the low meanders near the OH Valley. The trough will shift to 
the northeast. Drier air will build into our area with PWATs falling 
as low as 0.5". Models hint that during the day there could be some 
remnant showers far offshore (with the departing front) and towards 
the mountains (with the trough). But it appears we should stay 
within the dry air and see only clouds. The dry forecast continues 
into the night as high pressure in the Gulf builds towards us. The 
pressure gradient will be elevated, leading to gusty southwest winds 
in the afternoon, especially at the beaches. Below normal 850 mb 
temperatures and low heights will lead to below normal temperatures. 
Highs across the area may not reach the 70 degree mark. This will 
carry over into the night with lows falling into the 40s, warmer 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 centered over FL will spread 
across the Southeast into the night. Strong subsidence will bring 
dry conditions and sunny skies. Warmer 850 mb temperatures and 
rising heights will lead to seasonal temperatures.

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 continues. Temperatures should rise a 
few degrees above normal, but remain cooler at the beaches due to 
the sea breeze.


High pressure over the Southeast Monday night will remain nearly 
stationary into Tuesday, bringing dry conditions and above normal 
temperatures. The high starts to shift offshore Wednesday as a front 
approaches from the north. Models have this front weakening as it 
gets closer to us, meaning the rain threat should be low. Thursday 
the models diverge on the upper level pattern and the overall rain 
threat, so we went with a blend for the forecast.


KCHS: Thunderstorms have moved east of KCHS and a period of 
light rain will continue for a few hours. MVFR ceilings could
continue for another few hours as well, then go VFR this
evening. There is a low end chance for MVFR ceilings to develop
late in the period, but will keep VFR for now. Winds will be 
gusty once again on Saturday, frequently reaching the 25-30 knot

KSAV: Thunderstorms have pushed well to the east and all that is
left is lingering light rain that will persist for another
couple of hours. Thereafter, VFR conditions will prevail. Winds
will become gusty again on Saturday, with just a low end chance
of MVFR ceilings to develop. 

Extended Aviation Outlook: Gusty southwest winds Saturday


Quick update: Have canceled the Gale Warnings other than the
Charleston County waters. Elsewhere the line of thunderstorms
has passed through and disrupted the winds, but solid Small
Craft Advisory conditions will continue. Advisories have been
issued and run into Saturday. 

Saturday through Tuesday: A strong cold front will be moving 
off the East Coast Saturday morning while low pressure is near 
the OH Valley. The pressure gradient across the coastal waters 
will be elevated, leading to gusty southwest winds in the 
morning. Saturday afternoon the gradient will lower as the front
moves further offshore, allowing winds to ease. But it's a safe
bet that Small Craft Advisories will be up for all of the 
coastal waters and maybe even Charleston Harbor Saturday morning
due to winds and seas. These advisories should drop off by 
Saturday night. Broad high pressure will spread across the 
Southeast Sunday night, then prevail towards the middle of next 
week, bringing tranquil conditions.

Surf Zone Hazards: The High Risk of Rip Currents will continue
through this evening. Winds/seas have subsided enough to cancel
the High Surf Advisory everywhere other than Charleston County. 


GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117-
SC...High Risk for Rip Currents until 8 PM EDT this evening for 
     High Surf Advisory until 11 PM EDT this evening for SCZ050.
     Wind Advisory until 8 PM EDT this evening for SCZ050-052.
MARINE...Small Craft Advisory until 8 AM EDT Saturday for AMZ330-352-
     Gale Warning until 11 PM EDT this evening for AMZ350.