Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 281940
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
340 PM EDT Wed Sep 28 2016

.SYNOPSIS...
A cold front approaching from the west will slow down on Friday and
linger near or along the Carolina coast through this weekend. High
pressure will build in behind the front through early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 PM Wednesday...Convection has broken out along the
piedmont as expected, with a few showers/storms along the sea breeze
as well. A few of these storms have the potential to become strong,
especially far NW zones and just outside of the CWA, where
thermodynamics and forcing mechanisms best overlap. These include
height falls ahead of the deepening upper low, increasing low-level
winds around 850mb, SBCape of 3000 J/kg, and 0-6 km bulk shear
around 20 kts. Latest HRRR and 12z NSSL WRF are both modeling the
current situation pretty well, and expect most of the activity to
remain just outside the CWA border to the west, with the best chance
for any severe storms remaining well NW of the ILM CWA. That being
said, cannot rule out an isolated strong wind gust along i-95 this
aftn/eve, before diurnal heating wanes and storms weaken and
dissipate.

Tonight, a second round of convection is possible as a vorticity
lobe streaks up from the south, embedded in the mean flow between
the Atlantic Ridge and deep closed low to the west. Elevated
instability will remain, and forcing within this vort will be enough
to cause more showers with isolated tstms tonight, and this may
affect a larger portion of the CWA than will be impacted through
this eve. Do not expect strong or severe overnight, but more showers
will be possible and have continued CHC Pop through the overnight.
Temperatures overnight will remain above seasonable norms, with mins
dropping only to around 70.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 300 PM Wednesday...Synoptic pattern changes very little
through the end of the week, although sensible weather will improve
through the period. Deep upper low across the OH VLY will remain the
dominant feature as flow becomes very slow, keeping the closed low
basically stationary through the period. This will cause a cold
front to move slowly to the east, but guidance has backed off even
further on this motion, and it is now progged to not quite make it
to the coast even by Friday night. This will keep unsettled weather
with warmer temperatures across at least the eastern third of the
CWA, while locations out towards i-95 should still break into the
drier and cooler air, especially on Friday. This is noted by much
lower RH above 850mb advecting eastward in a dry slot beneath the
upper low. However, the large ridge across the Atlantic remains
strong, and forces the moist air ahead of the front and the dry slow
to remain along the coast, while the pinched flow between these
features drives vort impulses and shower chances northward into the
region. Friday will overall be a drier and slightly cooler day than
Thursday, that will be most felt well inland, while the immediate
coast may see little change with above climo temps and scattered
aftn convection.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 300 PM Tuesday...Latest model run keeps deep cutoff upper
low a bit farther west as it tracks up toward the Great Lakes over
the weekend. Therefore the sfc front and deeper moisture should remain
aligned parallel, just along the coast rather than off shore.
Plenty of dry air will wrap around the upper low into the
Carolinas aloft, but the lower dewpoint air behind the sfc
boundary may struggle to make it to the coast. Also, the sfc
boundary will remain a focal point for convective development and
although the air aloft will be drier, there should still be
shallow convection possible along and east of the boundary. There
will be a sharp gradient between the drier air to the west and
moister air to the east, but exactly where that will lie is tough
to say. The models are trending on keeping the boundary farther
west, along the coast, rather than off shore. This will mean more
clouds, showers and more humid air in place over the eastern half
or third of our area, but as you move inland there will be greater
amounts of sunshine and drier air. The latest pcp water shows
values up close to 2 inches from the tip of Cape Fear up to
Hatteras while west of I-95 will have PWATS less than an inch with
even lower amounts as you head W-SW. Essentially, the drier air
will wrap around from the SW aloft and N-NW at the sfc and it will
be more of a dewpoint gradient rather than temps. Daytime highs
will remain in the 80s most places. The guidance has backed off on
the cooler overnight lows due to the lack of lower dewpoint air
moving in, but I still think many places inland will get down
toward 60 early Sat.

As the the mid to upper low lifts north Sunday through early next
week, the lingering boundary will be pulled farther back on shore
as it dissipates through Monday. The winds should shift around to
the NE to E bringing some moister air back inland. Overall, places
inland and west of surface boundary will see a greater amount of
sunshine while places east of boundary will see a greater amount
of clouds and chc of pcp.

Heading into the middle of next week, the forecast become further
complicated by the differences in the models as to the track and
timing of Tropical Cyclone Mathew. For now, this system looks like
it will track westward and eventually turn up around the Atlantic
Ridge. The GFS is much faster with this system and we will have to
see how this evolves to determine how or if this affects the
southeast coast. For now, the greatest effects may be over the
coastal waters in pulses of swells and increasing gradient winds
eventually drive up the seas.

&&

.AVIATION /18Z WEDNESDAY THROUGH SUNDAY/...
As of 18Z...VFR conditions this afternoon and evening outside of
SCT 3SM TSRA BKN030CB across inland terminals KLBT/KFLO BTWN
22-02z. Isolated showers throughout region aft 02z as disturbance
aloft moves north over interior zones and ocean showers move
onshore at coastal terminals overnight into very early Thursday.
VFR Thursday 13z-18z as drier air spreads into the region with SKC
for most locations, TCU at end of TAF cycle.

EXTENDED OUTLOOK...Primarily VFR. Isolated to scattered afternoon
showers through much the period, although limited in strength and
coverage due to dry air aloft.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 300 PM Wednesday...Stalled front continues to sit NW of the
waters, with a weak pressure gradient remaining in place. Winds will
slowly veer from present S/SE to SW overnight, along with a slight
increase in speed from 5-10 kts to a more uniform 10 kts. This will
create seas of 2-3 ft, with a southerly wind wave and low amplitude
SE swell comprising the spectrum. Showers with isolated tstms will
be possible across the waters late tonight as well.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 300 PM Wednesday...Slow moving cold front will drag west to
east through the short term, finally approaching or stalling across
the waters Friday night. This will keep the waters in the warm
sector with S/SW winds of 10-15 kts expected through most of the
period, possibly shifting to the W/NW Friday night. These persistent
winds combined with the offshore high pressure will keep a 5-6 sec
southerly wind wave and 9-10 sec SE swell in the spectrum, creating
2-3 ft seas.

LONG TERM/SATURDAY THROUGH MONDAY/...
As of 300 PM Tuesday...A cold front will run parallel along or
near the Carolina coast...weakening through early next week.
Overall expect more northerly winds to come around to the NE to E
as weakening boundary gets drawn back westward as upper low lifts
off to the north through the period, but great variability is
possible. Seas will generally remain 2 to 3 ft over most waters
but a slight rise will be seen due to some longer period SE swells
mixing in through the weekend into early next week.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.

&&

$$

NEAR TERM...JDW
SHORT TERM...JDW
LONG TERM...RGZ
AVIATION...MJC



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