Area Forecast Discussion
Issued by NWS Wilmington, NC

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811
FXUS62 KILM 222325
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
625 PM EST Wed Nov 22 2017

.SYNOPSIS...
High pressure will build into the area overnight. Low pressure
over the eastern Gulf of Mexico will track slowly up from the
south Thursday through Friday, producing unsettled conditions.
The system will depart to the northeast on Saturday. A dry cold
front will move through Saturday night followed by cold, dry
Canadian high pressure through early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 630 PM Wednesday...Nothing but high clouds and a cool
northerly wind this evening with temperatures still expected to
drop into the mid-30s to mid 40s range by daybreak. Forecast
needs no adjustment other than to tweak the temperatures curve
in the gridded database. Previous discussion from this afternoon
follows:

Dry cold front has pushed off the coast, ushering in drier air
and helping to clear out lingering clouds low clouds. Only some
patches of cirrus linger over the region this afternoon. Mid-
level trough axis remains west of the area and the front lacks
any cold advection. High pressure building over the region in
the wake of the front shifts east tonight with northwest flow
becoming north and the northeast. The resulting northeast flow
will be what leads to a drop in temperatures for the remainder
of the period. Aloft the 5h trough axis remains west of the area
as a series of shortwave move around the base of the trough.
The trough digs over the central and eastern Gulf of Mexico
tonight and Thu as the first of several waves is ejected
northeast, moving up the Southeast coast.

The first wave will move across northern FL early Thu afternoon
then  head up the coast late in the day. Still some uncertainty
with respect to how close to the coast this feature will be. As
the shortwave emerges from the base of the 5h trough a surface
wave will develop along a front that will be stalled off the
Southeast coast and across central FL. The surface wave and it`s
mid-level partner will spread deep moisture and cloud cover
over the area but it currently appears that precipitation
associated with the feature will remain south and east of the
forecast area through the end of the period. Confidence in
precipitation chances late in the period is low. There will be
enough moisture and isentropic lift associated with the feature
moving northeast. A slight northward/westward shift of the
surface and mid level features would be all that would be needed
to end up with measurable rain late Thu. Temperatures tonight
will run near to slightly below climo, cooling off once the
northeast surge develops. On Thu highs will be kept below climo
by a combination of northeast winds and increasing/thickening
cloud cover.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 3 PM Wednesday...In the upper levels a large scale trough
will shift into the region and and bring a chance for showers
along the coast of southeast North Carolina and northeast South
Carolina.

The 12 UTC ECMWF, GFS, and Canadian are in some agreement in
keeping the bulk of the precipitation off the coast. The 12
UTC NAM closes off in the upper levels and brings heavy rain in
the entire area. While the Canadian is a bit more robust with
the precipiation along the coastal counties compared to the
ECMWF and the GFS. The 12 UTC GFS Ensemble agrees with the
deterministic ECMWF and GFS so trend into this direction with a
20 to 25% chance of showers mainly east of a Kingstree, SC to
Surf City, NC line through the forecast period. QPF values are
expected to be less than 0.10 of an inch for this event.

Temperatures will continue to be below normal with lows ranging
from the lower to middle 40s at the coast to the mid 30s well
inland on Thursday night. On Friday night lows will be 4 to 5
degrees warmer. Highs on Friday will be in the upper 50s to near
60.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 3 PM Wednesday...Primary weather caption for this time
frame remains `seasonably cool, and dry` as a series of upper
troughs progressively traverse the coast, the strongest of which
late Saturday, brings cold air advection Sunday.
The coolest portion of this time period looks to be daybreak
Monday, when high pressure becomes centered over the inland
Carolinas under clear skies at first light. The mildest portion
of this period will be Saturday afternoon, ahead of the
approaching, dry, cold front, and then again The breeziest part
of the forecast will be Sunday as high pressure builds in from
the west.
Late in the extended period for days 6/7, a return and moisture
flow slated, as a moderately strong upper trough digs into the
central MS Valley, hence, a warm air advection trend appears on
tap for next Tue/Wed, with a slight chance of rain as a warm
front arrives from the south in the return flow.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 23Z...High confidence for VFR conditions through the
forecast period. From models and BUFKIT moisture profiles are
not favorable for fog formation. Weak High pressure across the
region on Thursday will bring mostly sunny skies in the morning
but then with developing Gulf system we can see increasing high
clouds streaming into the area during the overnight period
continuing across the region on Thursday. North winds overnight
will become more Northeast on Thursday around 5-8kt.

Extended Outlook...VFR conditions expected through most of Thurs.
Low confidence for MVFR to IFR conditions near the coast late
Thursday through Saturday morning in low clouds and rain.

&&

.MARINE...
NEAR TERM /THROUGH THURSDAY/...
As of 630 PM Wednesday...Dry cold front has pushed east of
waters with high pressure starting to build in from the
northwest. The high will shift east tonight with winds veering
to north and then northeast. Gradient starts to tighten up as
the high shifts east and wind speeds will increase to a solid 20
kt in response. Northeast winds around 20 kt continue into Thu
morning before surge eases and the gradient relaxes. Winds will
drop closer to 15 kt by midday and will be on the high end of
the 10 to 15 kt range by the end of the period. Seas 3 to 5 ft
this afternoon start to build following the arrival of the cool
surge. Seas increase to 4 to 6 ft this evening and will remain 4
to 6 ft through Thu morning before starting to decrease as wind
speeds drop off. Did not alter inherited small craft advisory
headline which goes into effect this evening and continues into
Thu afternoon.

SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 3 PM Wednesday...The synoptic setup over the coastal
waters will see high pressure over the Carolinas and a frontal
boundary east of the coastal waters. On Friday the ECMWF and GFS
indicate a weak low pressure area will develop along the
frontal boundary and with propagate up this boundary east of the
coastal waters. The biggest impact will be in the waters south
of Myrtle Beach.

The winds will be from the northeast at the start of the period
and will back to the northwest as the low shift northeast of
the waters. Winds speeds will be around 10 to 15 knots with a
increase to 15 to 20 knot especially in the waters south of
Murrells inlet on Friday into Friday night. The wave models are
showing significant sea heights around 2 to 4 feet Thursday
night before increasing to 3 to 5 feet on Friday into Friday
night.

LONG TERM /SATURDAY THROUGH MONDAY/...
As of 3 PM Wednesday...A changeable marine period as a cold
front approaches Saturday, crosses the coast late Saturday
night and early Sunday, followed by building high pressure into
the area through the day Sunday.
Departing low pressure offshore Saturday, will leave moderate
W-NW winds along the 0-20 NM marine zones through Saturday. The
breeziest day and highest seas will be Sunday as North winds up
to 20 KT prevail, with a few higher gusts. Wave guidance
showing 4-5 feet offshore Sun, thus a cautionary headline may be
needed. As the high pressure center nears, N winds will veer to
NE and weaken on Monday.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory until 3 PM EST Thursday for AMZ250-252-
     254-256.

&&

$$

SYNOPSIS...99
NEAR TERM...REK/III
SHORT TERM...DRH
LONG TERM...MJC
AVIATION...MAC
MARINE...MJC/REK/III/DRH



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