Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 270924

Area Forecast Discussion
National Weather Service Wilmington NC
524 AM EDT Tue Sep 27 2016

A weak wave of low pressure moving just offshore will bring
showers today, mainly along the coast. A cold front approaching
from the west will stall through mid-week before moving across the
area on Thursday, maintaining warm and unsettled conditions. Cool
and dry high pressure will build into the area by the weekend.


As of 330 AM Tuesday...The story today will be a sfc low that
develops just offshore from the SC Coast and is progged to move NE
along an inverted sfc trof oriented SW to NE, and just offshore
and parallel to the Carolina coasts. The flow aloft in the mid-
levels will be increasing from the SW which will help accelerate
the coastal low to the NE to off Cape Hatteras by daybreak
Wednesday. POPs across the coastal counties will be borderline
high chance to likely, then dropping off to low to moderate chance
as you push further inland. The pcpn/convection across the far NW
portions of the ILM CWA, ie. west of the I-95 corridor, will be
from a sfc cold front located over the western portions of the
Carolinas this morning. Models indicate this cold front will track
off to the east toward the Carolina coasts, but only at a turtle`s
or snail`s pace. The other story for the near term period will be
the evolution of the closed upper low that will be dropping
southward to the southern Great Lakes by Wed daybreak. This will
produce the increased SW flow aloft across the FA which
accelerates the coastal low to the NE as mentioned earlier.
Temperatures will be a consensus of model mos guidance with
emphasis on the European guidance.


As of 400 AM Tuesday...Models are in an o.k. agreement in the
closed upper low becoming a cutoff upper low during this period,
as it breaks off from the main belt of the westerlies aloft. The
cutoff low will drop southward, reaching the Central Appalachians
by Friday daybreak. The extremely slow moving cold front from the
near term period, will only reach the Carolina coasts toward late
Thursday night. Forcing ahead of the cold front will alone keep
POPs active Wednesday into Thursday. However, and additionally,
dynamics associated with vorts or s/w trofs rotating around the
upper cutoff low, like spokes on a bicycle, may combine with the
sfc frontal dynamics. And, if this occurs during the max heating
of the day, then there will be a possibility that a few strong to
severe thunderstorms may occur especially on Wednesday and to a
lesser degree during Thursday. The FA does not get directly
underneath the cold pool aloft, ie. exhibiting steep lapse rates,
associated with the cutoff low. But nevertheless, temps aloft are
progged to lower just not to the extreme under the cutoff low
itself. Will highlight in the HWO the isolated threat for strong
to sever convection. On a side note, SPC does have the ILM CWA
within a marginal area on Wed. POPs will generally be hiest in the
aftn thru early evening each day. And will carry a low POP during
the overnights and early morning hours. Daily MAX/MIN temperatures
will run 1 to 2 categories hier than the climo normals thruout
this period.


As of 300 AM Tuesday...The extended remains a rather lower than
average confidence forecast due to discrepancies in the guidance
handling an anomalous cut-off low across the OH VLY. The ECM
continues to be a slow outlier, but once again the GFS/CMC, which
are in very good agreement today, have slowed from previous
solutions. This continues to lend some support to the ECM, and a
slower progression of the mid-level and surface features is likely,
just not quite to the extent the ECM continues to advertise. While
this upper low spins and ejects only very slowly NE through the
wknd, the surface cold front beneath it will drift east, crossing
the local area late Thursday, before being replaced by Canadian high
pressure. This suggests that cooler and drier conditions will be in
place for the majority of the extended, with temps at or slightly
below seasonable norms, and a nice early fall weekend is possible.
Must continue to note however that if the ECM ends up correct, this
front may not cross until Saturday, leaving much warmer and
unsettled conditions in place through the first half of the wknd.


As of 06Z...Slow moving cold front well NW of the terminals, and a
developing weak low pressure along the coast, will maintain ample
cloudiness and possible showers through the valid period. A few
showers have developed in the short term forecast period will be
marked with a cold front sliding into the forecast area and then
stalling. This front will be a focal point for showers and
isolated thunderstorms each day.

On the synoptic scale a large upper-level low just north of Lake
Superior will shift to Ohio Valley by Wednesday night. This feature
will be bringing a significant air mass change but this does not
begin until after the short term forecast period.

The slow moving cold front will be the focus for the heaviest rain
on Wednesday into Wedensday night with QPF values running between
just over 1". Maximum Temperatures on Tuesday and Wednesday are
expected to rise to the middle 80s with the warmer temperatures west
of Interstate 95. For lower temperatures values will range from the
upper 60s inland to the lower 70s at the coast.long the coast so
far this morning, and this is likely to continue through daybreak.
Do not expect coverage to be widespread enough for a VCSH mention,
so have added a TEMPO group at ILM/CRE/MYR for periodic and brief
MVFR. The inland terminals will likely remain dry as the showers
along the cold front to the NW are forecast to dissipate as they
drop SE. While cloud cover will be significant, much of it will
remain the mid-levels, so light fog is possible overnight at
LBT/FLO, with winds just above the surface likely too strong for
any IFR vsby restrictions.

Scattered showers will again be possible during Tuesday aftn/eve,
but coverage is expected to be light enough that no mention of any
restrictions has been added attm. Best chance for showers during the
day will be along the coast, but will handle this potential with
later updates. Winds will be generally from the east and less than
10 kts beneath VFR cigs. More stratus will again be possible Tuesday
night, especially along the coast.

EXTENDED OUTLOOK...Scattered SHRA/TSRA Tuesday through Thursday.
Cold frontal passage Thursday. VFR expected fRI/SAT.


As of 330 AM Tuesday...Winds and seas will be driven by the
inverted sfc trof and the weak low moving NE along it. This will
result in an easterly flow at the start of this period. Winds will
veer to the SE to S this afternoon and evening, and to the SW
overnight. The sfc pg will remain somewhat relaxed except as the
low passes by. Wind speeds generally 10 to 15 kt, except a more
solid 15 kt with possible gusts to 20 kt as the low passes across
the ILM NC Waters and temporarily continuing in the wake of this
low. The reason for the hier winds and Significant seas will run
2 to 4 ft north of Little River Inlet and 2 to 3 ft south of this
Inlet. The ese 1 to 2 foot ground swell at 7 to 8 second periods
will dominate the seas spectrum initially. Wind generated waves at
4 to 5 seconds will become dominate during and after the passage
of the low. Scattered to areas of convection will affect the
waters thruout this period, with the best coverage occurring
today into this evening.

As of 400 AM Tuesday...The area waters will be under the influence
of an expansive cutoff low that drops southward to the Central
Appalachians by the end of this period. A sfc cold front out ahead
of this cutoff low, will continue at a snail`s pace to the east,
finally reaching the coastal waters during late Thursday Night.
SSW to SW flow will dominate the local waters Wednesday into Thu,
then veer to the W and NW depending on the extent the cold front
pushes to or partially across the local waters. The sfc pg will
slowly tighten-some with time due to the approaching cutoff low.
Initially, wind speeds at 5 to 10 kt, then increasing to 10 to 15
kt or around 15 kt, Thu into Thu night prior to the cold front
reaching or partially moving across the local waters. Significant
seas will hoover, no relation to the vacuum, right around 3 ft.
Some fluctuations of 1 foot either higher or lower than the 3 ft
will occur. For the most part, wind waves at 4 to 6 second periods
will dominate. No underlying 1 to 1.5 foot easterly ground swell
at 8 to 9 second periods will be present. Convection may become
strong to possibly severe during Wednesday and again on Thu.

As of 300 AM Tuesday...A cold front will slowly move across the
waters on Friday, causing winds to shift from SW at 5-10 kts early,
to NW at 5-10 kts late. As high pressure builds down into the area
behind this front on Saturday, winds will shift further to the NE,
but remain at relatively weak speeds due to the weak pressure
gradient. Seas will be 2-3 ft Friday with a southerly 5-6 sec wave
being the predominant wave group. By Saturday, wave heights will
fall to around 2 ft, possibly building again late in the period as
some forerunner swell from a developing tropical system well out in
the Atlantic enters the waters.




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