Area Forecast Discussion


584 
FXUS62 KCHS 180935
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
435 AM EST Sun Feb 18 2018
.SYNOPSIS...
A front will meander across the region today, before lifting
north on Monday. High pressure will then prevail for much of
the week. A cold front could approach from the north Friday
before high pressure returns during the remainder of the
weekend. Another cold front should approach the area early next
week. 
&&
.NEAR TERM /THROUGH TONIGHT/...
Pre-dawn: Temps have been mild overnight, ahead of a secondary 
cold front which will reach our northern zones nearing daybreak.
While skies have been mainly clear, stratocu was increasing over
northern and western zones. Another round of advection stratus 
is also on tap for southeast GA to the south of I-16, patchy fog
is in the forecast with the surge of low level moisture.
Today: Mid and upper level flow will be mostly zonal atop a strong 
anticyclone blanketing an expansive area from the Gulf of Mexico
to the Bahamas. Surface high pressure will build from the Ohio 
Valley to the Mid Atlantic by later today, while the front 
stalls to the south of our forecast area. We will see an increase
in layered clouds today across the region with all areas expected
to run a bit cooler today, especially in southeast GA where highs
should only reach the mid 70s to the south of I-16. 
Chances for measurable rains appear low given the lack of any
significant forcing aloft. However, we do see a general increase
in moisture below 700 MB, especially across our SC zones later
today. We placed slight chance POPs across some inland zones 
but we could see some isolated showers further east late this 
afternoon.
Tonight: Warm air advection processes build atop a weak wedged
surface air mass while a coastal trough develops offshore. This
is a recipe for stratus development and a potential build-down
fog scenario, resulting in some widespread late night fog
coverage. To introduce, we painted patchy fog across the region.
There will also be spotty showers around and perhaps some late 
night drizzle where stratus is more prevalent. Lows most areas 
will be in the mid/upper 50s.
&&
.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
Monday: A warm front will quickly lift north late morning into early 
afternoon, favoring a few showers over parts of Southeast South 
Carolina through late afternoon. Temps will be noticeably warmer as 
a ridge of high pressure begins to build over the area from the 
Atlantic. In general, afternoon temps will be some 15 degrees above 
normal for this time of year, peaking in the upper 70s to lower 80s. 
Monday night lows will remain mild, dipping into the upper 50s/lower 
60s. Precip free conditions are expected during overnight hours, but 
sfc dewpts near 60 and potentially some stratus building down 
suggest higher fog probabilities late. Patchy fog has been included 
for all land areas after midnight. 
Tuesday and Wednesday: Warm weather is expected through midweek 
while a ridge of high pressure centered over the Western Atlantic 
continues to build over much of the Southeast United States. 
Although most areas will remain dry, a few showers will be possible 
over inland areas along the western edge of ridge each afternoon. 
Temps will be well above normal each day, potentially reaching 
record breaking levels Wednesday afternoon. In general, highs should 
peak in the lower 80s away from the coast each afternoon. Lows will 
be mild, remaining in the lower 60s Tuesday night. Patchy fog could 
be an issue late each night as a southerly wind helps maintain lower 
60 dewpts over the Southeast.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
A large ridge of high pressure centered over the Western Atlantic 
will be the primary contributor to the pattern over the Southeast 
United States, helping produce warm conditions into late week. In 
general, temps will be well above normal, peaking into the upper 
70s/lower 80s Thursday afternoon. A few showers will be possible 
well inland during peak heating Thursday when mid-lvl energy 
approaches western areas. A weak cold front will attempt to approach 
from the north Friday, potentially producing a few showers over 
Southeast South Carolina, but high pressure should quickly return 
and persist through much of the weekend. High temps should be a 
degree or two cooler over the weekend, but will remain well above 
normal for this time of year. In general, highs should range in the 
upper 70s to lower 80s away from the coast. More substantial precip 
chances should arrive with a cold front approaching from the west 
early next week.
&&
.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
VFR conditions overnight but MVFR could return at times behind 
a cold front toward daybreak and through Sunday morning. IFR
cigs may make a run at KSAV toward daybreak. Models suggest 
lower clouds will expand this evening with a good chance for 
MVFR or lower cigs tonight.
Extended Aviation Outlook: Flight restrictions are possible Tuesday 
and Wednesday night, mainly due to low stratus and/or fog late each 
night. Otherwise, VFR conditions should prevail.
&&
.MARINE...
A cold front will move through the waters this morning and then 
tend to wash out to the south of the GA waters later in the day. 
Latest guidance has been trending stronger with pinching thermal
and moisture gradients across central SC waters this afternoon.
Numerical marine MOS values were now showing nearly 20 kt of
sustained NE flow at FBIS1 out to Buoy 41004. Inspection of the 
925 MB thermal gradient with a 6C temp gradient across Berkeley 
& Charleston Counties suggest northern waters will see a period
of locally enhanced onshore flow later today. We raised a SCA 
for the afternoon hours in our Charleston waters for 20G25 kt 
conditions. Seas will build from 2 ft early to 3-4 ft. Otherwise,
winds will turn NE with much lighter flow over GA waters. 
Tonight: A weak coastal trough will develop with winds likely
to remain NE with speeds below 15 kt and seas 2-4 ft.
Monday through Friday: A front will quickly lift north of the waters 
on Monday, followed by a period of high pressure extending over the 
western Atlantic through late week. The pattern suggests fairly 
quiet conditions over all coastal waters in regards to winds/seas. 
However, lower 60 dewpts will likely spread across the coastal 
waters through midweek, potentially leading to some sea fog issues 
over cooler nearshore waters. East/southeast winds on Monday will 
become southeast on Tuesday, then south/southeast by late week, 
remaining at or below 10-15 kt. Seas will slowly build to 2-4 ft in 
nearshore waters and peak near 4-5 ft in offshore Georgia waters 
late week. 
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from noon today to 6 PM EST this evening 
     for AMZ350.
&&
$$
NEAR TERM...
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...DPB
MARINE...DPB