Area Forecast Discussion
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FXUS62 KILM 211740
Area Forecast Discussion
National Weather Service Wilmington NC
1240 PM EST Sat Jan 21 2017
A warm front will meander across the region of the carolinas
today into Sunday. A more complex and potent storm system will
affect the Carolinas Sunday into Monday with potential for
severe weather during Sunday afternoon and evening. Total
rainfall amounts today through Monday should amount to one to
three inches. This storm system will slowly depart through
Monday leaving high pressure for Tuesday and Wednesday. The next
cold front will move across the area on Thursday.
.NEAR TERM /THROUGH TONIGHT/...
As of 1100 AM Saturday...Dense Fog Advisory has expired for all
areas across the forecast area as fog lifts and visibilities
continue to improve. Frontal boundary remains draped from west to
east almost directly cutting the NC/SC border with some light pcp
along and off the coast. Area of heavier rain with isolated
thunderstorms was just creeping in from the south into northeast
This boundary will shift north back north as warm front through
early this afternoon. Sfc winds will come around leaving a deep
warm and moist S-SW flow across the area. Models continue to
show a sfc low moving along this boundary as a shortwave tracks
up from the SW. As the low exits off to the north overnight the
boundary will get a slight push south again but it looks like
it should be aligned closer to the VA/NC border by Sun morning
leaving our forecast area well entrenched in a warm and moist
air mass overnight. The best shortwave energy will move across
the area this afternoon through this evening with periods of
heavier rain and isolated thunder possible. Strongest convection
will remain west aligned with low which should move through the
western Carolinas between 4 and 8pm.
Expect a break in pcp overnight with another period of low
stratus and fog with temps and dewpoints remaining near 60.
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 445 AM Saturday...This will become a busy period of
changing wx conditions due to the progressive flow basically
occurring at all levels. All eyes turn toward the potent upper
closed low over Louisiana at sunrise Sunday. This closed upper
low does intensify as it moves from Louisiana ENE to the Western
Carolinas by daybreak Mon. Looking at the GFS, European, NAM
and SREF model comparisons...and for the most part they all
agree thru 72 hrs with the mid-level closed Low over Virginia by
Monday evening. Its the time line there-after is when the
models diverge from one another`s solutions. For Sunday thru
Sunday night, is the time period when the upper low captures the
sfc low. By Sunday evening, an occluded front will extend from
the captured low to the Carolinas Coasts. Aloft, the dynamics
associated with the upper closed low along with the twisting and
turning of the winds from the sfc to aloft will favor a
hodograph that signifies tornadic possibilities. Will definitely
have the wind shear from both increasing speeds from the sfc
thru aloft and also wind shear in terms of wind direction
changes as one goes up thru the atmosphere. The amount of
instability avbl will be in question in order for this severe wx
The old saying, high Shear, low Cape maybe just enough input
from each for svr thunderstorms to develop with this event.
I`ve seen where 60+ kt winds were howling less than 1200 ft AGL,
but with no avbl CAPE for thunderstorm activity to develop and
tap those low level jet winds in bringing them down to the sfc.
The overall time-line SVR Threat will be from Sunday mid to
late afternoon across the SW portions of the ILM CWA...moving
across and exiting NE of the ILM CWA by mid to late Sunday
evening. Will highlight the Severe potential in the Hazardous
The stacked low will drift across VA and off the VA Cape by
Tuesday daybreak. The sfc cold front pushes well east of the FA
late Sunday night thru Monday. Enough moisture will wraparound
aloft, keeping the FA within cloudiness along with a low POP for
either light showers or patchy light rain or drizzle. There just
isn`t any cold air avbl for any type of Wintry Pcpn chances to
worry about given this type of system and the Winter season we
are currently are in. Overall, temps thru this period will start
well above normal, ie. 15 degrees above normal. And will end
with temps 5 to 10 degrees above normal.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 300 AM Saturday...Impressive stacked low will be exiting
to the northeast Tuesday morning with weak mid level ridge axis
to the west shifting overhead. 5h ridge does expand north
slightly Tue into Wed, increasing mid level subsidence, but it
shifts off the coast by midday Wed. Under the mid level ridge a
weak surface high will build in from the west. The high is a
modifying maritime tropic airmass and lacks cold air. As a
result temperatures Tue and Wed will remain well above climo.
Mid level subsidence and a lack of deep moisture helps keep the
region free of precip as well as limiting cloud cover.
A cold front, trailing low pressure moving from the eastern Great
Lakes to southeast Canada Wed into Thu, moves into the area Thu.
Deep southwest flow ahead of the front will help spread Gulf
moisture over the region. Precipitable water values approach 1.5
inches just prior to fropa and there should be some potential for
isolated showers, especially if a slower solution similar to the
latest GFS, verifies. GFS also depicts a weak wave developing along
the front prior to the boundary reaching the forecast area. ECMWF is
a little faster with the front (in part because it doesn`t develop
the surface wave). While temperatures ahead of the front will be
well above climo, the passage of the front begins a downward trend
in temperatures as another high builds in. Temperatures will be near
climo for Fri and then below climo on Sat. The cold air does not
arrive in 1 big surge, instead it oozes into the southeast over a
period of a couple days.
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 18Z...Difficult flight conditions as periods of IFR and
MVFR prevail this TAF cycle. The onshore flow will also plague
coastal terminals at times with VSBYS < 1/2 NM. -RA/SHRA also in
the mix 22Z-02Z, then again Sunday AFT 14Z. Winds mainly SSE-SSW
this period at speeds of 11KT or less.
Extended outlook...Thunderstorms are expected on Sunday
with IFR conditions possible. There is potential for strong to
severe thunderstorms Sunday afternoon into the evening.
Monday thru Wednesday, MVFR to mainly VFR conditions expected.
NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Saturday...SCA for all coastal waters beginning
at 6 am Sunday and persisting thru 6 pm Tuesday.
A sfc frontal boundary will be meandering across the local
waters this period. At first, it will lift northward as a warm
front this aftn and then drop back to the south slightly tonight,
likely stalling across or just north of the region. Therefore
winds to the north of this boundary will shift from E-SE to S-SW
through the day and south of the boundary the winds will be SW. Wind
speeds will see a lull this morning thru this aftn, then pick
up to 10 to 20 kt by daybreak Sunday as the meandering front
moves north of area waters. Thus the ILM Waters will remain in
the warm sector under increasing S to SW winds. Will indicate
isolated thunder across the waters, mainly across waters that
have SSTS near 60 degrees which for the most part are the
offshore waters. Significant seas will be at their lowest today
when compared to what they will become during the next 3 days.
The seas will begin their rising trend tonight with 3 to 5
footers possibly by daybreak Sunday. Wind driven waves at 5 to 6
second periods, will dominate the significant seas spectrum
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 445 AM Saturday...SCA thresholds to be met by Sunday
morning and will persist thru Tuesday daybreak. Much will depend
on the behavior and potential strength of the mid-level closed
low that captures it`s sfc companion and becomes vertically
stacked by the end of this period. For 2 to 3 days out, the big
4 models are in decent agreement with one another with regard
to the intensity and timing of this eventually stacked system.
When you observe 990`s and 980`s sfc lows being advertised
across the ILM CWA, then for Marine purposes, a SCA is a "given"
with an increased potential for Gale Warnings may be needed
especially when models indicate 980`s sfc lows moving in the
vicinity. I may be underdone with the winds for Monday as I
remained somewhat skeptical of various model solutions. Will be
looking atleast at 20 to 30 kt windspeeds with hier gusts.
Significant seas will have already been on the increase at the
start of this period. Ww`ll likely be pushing atleast 10 ft
just outside of the ILM coastal waters off Cape Fear and Romain.
The only "saving grace" is that winds will be veering to the WSW
to WNW, ie. Offshore trajectory, late Monday, thus limiting the
avbl fetch for significant seas to build upon from.
LONG TERM /TUESDAY THROUGH WEDNESDAY/...
As of 300 AM Saturday...Strong offshore flow to start the
period will gradually subside during Tue as high pressure builds
in from the west. Conditions Tue morning will likely require
headlines but unsure if SCEC or SCA will be warranted. Gradient
gradually relaxes Tue with speeds dropping under 15 kt Tue night
as winds veer from northwest to southwest. Surface ridge axis
moves overhead Wed morning with speeds around 10 kt. Ridge axis
shifts offshore Wed with a steady increase in southwest winds in
the afternoon and evening. Solid 15 kt southwest winds Wed
afternoon will increase to 15 to 20 kt Wed night. Offshore flow
Tue leads to a steady reduction in seas, dropping from near SCA
thresholds Tue morning to 1 to 3 ft Tue night. Southwest flow
developing and then increasing Wed will start building with
values peaking between 3 to 5 ft late Wed and Wed night.
MARINE...Dense Fog Advisory until 6 AM EST Sunday for AMZ250-252-254-
Small Craft Advisory from 6 AM Sunday to 6 PM EST Tuesday for