Area Forecast Discussion
Issued by NWS Wilmington, NC
FXUS62 KILM 271349
Area Forecast Discussion
National Weather Service Wilmington NC
950 AM EDT Tue Sep 27 2016
A weak wave of low pressure moving just offshore will bring
scattered showers and a few thunderstorms 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.
.NEAR TERM /THROUGH TONIGHT/...
As of 940 AM Tuesday...A weak area of low pressure off the GA/SC
coast this morning is expected to move northeast along a coastal
trough during the day. The precipitable water will be above 1.8
inches along the coast, while the bulk of the tropical moisture will
remain offshore. The HRRR is not that robust regarding rainfall
chances and abundant cloud cover will likely hamper significant
destabilization. Thus lowered the POPs, but still expect to see
scattered showers and a few thunderstorms develop around the
forecast area through the evening. Otherwise, the cold front across
far western NC will only slowly move east through tonight. Currently
favor the cooler MAV numbers, especially across the eastern portion
of the forecast area where clouds will inhibit heating the most.
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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
.LONG TERM /FRIDAY THROUGH MONDAY/...
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.
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
As of 12Z...Low pressure off the South Carolina coast combined with
a weak frontal boundary to our west will keep convection in the
picture through the afternoon hours. Time height indicates quite a
bit of mid cloud around today, so we will only get moderately
unstable at best. Light northeast winds this morning will become
easterly and onshore this afternoon. Light winds tonight with some
light fog possible after midnight.
EXTENDED OUTLOOK...Scattered SHRA/TSRA Tuesday through Thursday.
Cold frontal passage Thursday. VFR expected Friday/Saturday.
NEAR TERM /THROUGH TONIGHT/...
As of 940 AM Tuesday...Weak trough along the coastal waters will
result in variable winds across the SC waters and maintain easterly
flow across the Cape Fear waters. As low pressure off the GA/SC
coast moves northeast during the day expect easterly winds across
all waters. The pressure gradient is fairly weak and wind speeds
will remain around 10 knots through tonight. Scattered showers and
a few thunderstorms are possible through tonight as well.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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.
LONG TERM/FRIDAY THROUGH SATURDAY/...
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.