Area Forecast Discussion


909 
FXUS62 KCHS 130900
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
400 AM EST Wed Dec 13 2017
.SYNOPSIS...
Dry high pressure will persist across the region through Thursday. A 
cold front will push through the area Friday before high pressure 
prevails Saturday and Sunday. Another cold front will shift over the 
region Monday into Tuesday before high pressure returns during the 
middle of next week.
&&
.NEAR TERM /THROUGH TODAY/...
There will be a brief cool down today a fresh cP airmass settles
across the Southeast U.S. in the wake of a cold front which 
pushed offshore yesterday. The strongest push of post-frontal 
cold air advection has propagated well offshore and the low-
level advection pattern will become neutral to warm later in 
the day as a secondary cold front approaches from the northwest.
H8 temperatures as cold as -2 to -4C will recover 4 to 6C by 
late afternoon with corresponding 1000-850 hPa thickness rising 
to 1320-1330 meters under full insolation. This should support 
highs from the upper 40s/near 50 across the Charleston Tri- 
County area to the lower 50s across much of Southeast Georgia in
the absence of a downslope component.
&&
.SHORT TERM /TONIGHT THROUGH SATURDAY/...
Tonight: A secondary cold front will push offshore overnight and
be followed by another brief yet weaker surge of cold air 
advection as the supporting shortwave passes by well to the 
north. Mainly clear skies will prevail overnight, although some
cirrus associated with the subtropical jet will approach 
Southeast Georgia prior to daybreak Thursday. Lows will range 
from the mid 30s inland to the lower-mid 40s at the coast. 
Breezy conditions will occur at the beaches with gusts at or
above 30 mph at times.
Thursday: Dry sfc high pressure will prevail over the Southeast 
along the base of a large and broad mid/upper trough of low pressure 
extending from the Central United States to the Northeast United 
States. The pattern favors quiet weather, but temps will be 
noticeably warmer than the previous day as low pressure passes to 
the north and helps produce a west/southwest flow over the 
Southeast. In general, afternoon highs will approach the lower 60s 
over most areas. A few locations could peak in the mid 60s south of 
I-16 in Southeast Georgia. A light west/southwest flow will continue 
through Thursday night, keeping temps a few degrees warmer than the 
previous night. In general, temps should dip into the favoring a 
warmer trend compared to the previous night. In general, Thursday 
night lows should range in the upper 30s inland to mid 40s near the 
coast.  
Friday: A cold front will push through the region early this weekend 
with little in regards to precip. However, a few showers can not be 
ruled out near the coast as the front shifts offshore late. Upper 
lvl-moisture along with strong divergence associated with the right-
rear quadrant of an upper lvl-jet should also produce some high 
clouds for most areas away from the coast. Given the setup, temps 
should remain a bit cooler inland where high clouds and fropa occur 
first. In general, temps will peak in the upper 50s inland to 
low/mid 60s near the coast. Dry and cold high pressure will push 
into the area Friday night. Lows should dip into the lower 30s 
inland to mid/upper 30s closer to the coast. 
Saturday: Conditions will remain quiet as dry high pressure becomes 
centered over the Southeast. Despite a full day of sun and 
downsloping wind component, temps will remain below normal. In 
general, afternoon highs will peak in the mid/upper 50s over most 
areas. 
&&
.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
High pressure centered over the area Saturday night will lead to 
strong radiational cooling and temps that dip into the mid/upper 30s 
inland to low/mid 40s near the coast. Conditions will then become 
noticeably warmer on Sunday as a light southerly wind develops on 
the west side of high pressure shifting offshore. Temps should 
approach the mid 60s Sunday afternoon before clouds develop as 
moisture and isentropic ascent increase late. The next chance of 
showers should begin Sunday night and increase in coverage on Monday 
as a plume of moisture characterized by PWATs near 1.75-2.0 inches 
advects over the Southeast along/ahead of a cold front approaching 
from the west. Temps could peak into the upper 60s to near 70 
degrees on Monday before fropa occurs. Models insist that mid-lvl 
energy will traverse over the Southeast before the main mid-lvl 
trough axis passes over the area on Tuesday. For this reason, at 
least slight chances of showers will be possible Monday night into 
Tuesday before dry high pressure returns mid week.
&&
.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
VFR.
Extended Aviation Outlook: VFR conditions will prevail at both CHS 
and SAV terminals through this weekend. 
&&
.MARINE...
Today: Conditions will rapidly improve across the coastal waters
this morning as high pressure builds in from the west. Winds and
seas will remain elevated enough to maintain Small Craft
Advisories for a few more hours for all but the Charleston
Harbor where the advisory will be cancelled a few hours early.
Northwest winds will steadily back to the west and southwest
this afternoon as the surface high shifts south of the waters. 
Tonight: Southwest winds will pick up this evening as low-level
jetting intensifies with the approach of a dampening shortwave
and associated secondary cold front. Expect winds to reach 20-25
kt over the waters with 15 kt in the Charleston Harbor. Seas
will correspondingly build, reaching 3-5 ft nearshore waters
with 5-6 ft offshore waters. Small Craft Advisories will be
issued for all legs with the exception of Charleston Harbor.
Could see gusts to 25 kt occur in the Harbor entrance, but will
hold off on raising flags for the Harbor with this forecast
package. 
Thursday through Sunday: Small Craft Advisory level conditions will 
likely continue for most coastal waters into Thursday morning while 
cold air advection helps promote low-lvl mixing into a 40 kt low-lvl 
jet. Winds/seas should then improve late Thursday morning with 
nearshore waters likely falling below Small Craft Advisory levels by 
noon. Offshore Georgia waters could see Small Craft Advisory level 
conditions linger into early afternoon. Dry high pressure will then 
prevail Thursday evening and night ahead of a cold front approaching 
the waters on Friday. Conditions could approach marginal Small Craft 
Advisory levels over northern South Carolina waters and offshore 
Georgia waters behind the front Friday night into early Saturday. 
Winds/seas will then remain well below Small Craft Advisory levels 
as high pressure becomes centered over the area on Saturday and then 
slowly shifts offshore on Sunday. 
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 10 AM EST this morning for AMZ350-
     352-354-374.
     Small Craft Advisory from 10 PM this evening to 10 AM EST 
     Thursday for AMZ350-352-354.
     Small Craft Advisory from 10 PM this evening to 1 PM EST 
     Thursday for AMZ374.
&&
$$