Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 150513

Area Forecast Discussion
National Weather Service Wilmington NC
1213 AM EST Mon Jan 15 2018

Cold and dry high pressure will hold into Tuesday. An area of
low pressure will develop off the coast mid-week, bringing a
period of light wintry precipitation Wednesday and Wednesday
night. Arctic air will reach the area late Wednesday and
Thursday. Temperatures will begin to climb Friday, rising into
the 60s next weekend.


As of 1034 PM Sunday...No significant changes made in the late
evening updates, the trend to partly cloudy looks okay for the
SE NC coast. The leading edge of these clouds can be seen
thinning upon encountering the drier continental air near-shore,
with land dewpoints in the teens along the coastal interior.

As of 728 PM Sunday...Clear skies prevailed this evening with
unlimited visibility, and below normal temperatures, already
below freezing in many locals. 15 kft clouds moving at 55-60 kt
across north GA and western SC, will have minimal impact on
sensible weather or hourly temperature curves across NE SC and
SE NC overnight. Looking offshore, the western edge of a 3 kft
strato-cumulus deck, was making landward progress. Current
forecast appears to account for the moisture intrusion, and
little edits were needed, as portions of the north coast and
Cape Fear region become impacted by the encroaching clouds. This
in turn may slow cooling several degrees in these coastal
zones, and the current forecast minimums reflect this horizontal
temp gradient. Wind chills will range between 10-15 deg at
daybreak, although winds will be 10 mph or less generally, air
temps will be a couple degrees either side of 20.

As of 300 PM Sunday...Arctic high will shift from the OH Valley to New
England later today and tonight as it continues to extend down the
east coast. Skies will remain mostly clear overnight, although
forecast soundings are suggesting there could be some low cloud.
This appears similar to what forecast soundings were showing last
week when no cloud developed. Thus will not go for any low cloud but
soundings also suggest there could be some patches of thin cirrus at
times overnight. Although the gradient steadily weakens overnight do
not think the boundary layer will completely decouple. A few
sheltered areas and cold spots could, but winds under 5 mph will not
be the norm. Still, northerly flow will be a good bit lighter than
it was last night and with mostly clear skies lows will end up well
below climo. Some areas will dip into the upper teens with most of
the area in the lower 20s.

Northerly flow continues on Mon but with the elongated ridge axis
just west of the area north to northwest flow will be lighter. Lack
of any advection and an abundance of sunshine allows for some
airmass modification, but with temps starting out close to 10
degrees cooler than this morning highs will remain well below climo,
peaking in the mid 40s at the warmest locations. Airmass remains
very dry with precipitable water at or below 0.30" Mon and relative
humidity will once again dip under 30% in the afternoon.


As of 300 PM Sunday...High pressure stretched from north to south
over the Carolinas, will weaken as a potent mid to upper level
trough pushes a cold front east, into the Carolinas Tues night
into Wed. Overall, the air mass will modify through the period
with increasing moisture toward Wed morning. Temps Mon night
will drop into the mid 20 most places under decent radiational
cooling conditions as the sky remains mainly clear and winds
near calm. Warm and moist advection through Tues will help to
bring temps up around 50 most places and give a boost to
dewpoint temps bringing them up near 30 by the end of the day.

Moisture will increase in the mid to upper levels as digging
H5 trough pushes eastward. This will throw some mid to high
clouds across the western portions of the area Tues night.
Sounding profiles show moisture increasing through the column
above 13k ft mainly west of I-95. The GFS is a bit faster with
system and shows a greater increase in cloud cover. Overall
expect some increase in clouds Tues night, mainly after midnight
but any pcp holding off until later on Wed. Therefore, may see
temps drop out with better radiational cooling conditions to
start the night allowing temps to fall to 30 to 35 most places,
but may see a slight rise in temps once clouds arrive.


As of 300 PM Sunday...A brief Arctic blast and light wintry
precipitation Wed-Thu and then a warm up as more dry weather
returns. The risk for rain showers will return at the tail end
and just beyond this forecast period.

The latest NAM has bolstered the latest European solution with
precipitation developing ahead of a vigorous upper low and
associated shortwave energy. The upper trough is expected to
swing across the FA late day Wed and Wed night. The upper low
will move off the Mid-Atlantic coast Thu morning. In the wake
of this system, 850 mb temps will drop to minus 8 to minus 12C
Wed night as Arctic air briefly builds across the eastern
Carolinas. The Euro has latched back on to the solution of a
coastal low and the NAM depicts a coastal low as well. However,
the NAM is weaker and further off the coast with its depiction
than is the Euro model. If the Euro does verify, then more
precipitation may clip the coast Wed morning and this bears
watching. Otherwise precipitation should be increasing from W to
E as lift associated with the upper trough increases. Isentropic
upglide may also allow precipitation to break out across the
eastern Carolinas.

The column is supportive of frozen precipitation early on Wed
and then again late Wed and Wed eve. At this time, the brunt of
the precipitation is slated to fall Wed afternoon to early eve.
QPF is forecast to be a tenth of an inch or less. Factor in mix
and changeover to rain and slow column moistening and this
looks like a very light to no snow accumulation event. At this
time, we do show some accumulation of snow, a tenth of an inch or
two, across portions of our NW zones and NE zones where ice in
the cloud and low level thermal structure may line up best for
brief accumulating snow. Wind chill values overnight Wed and Thu
morning will be in the single numbers and a Wind Chill Advisory
may be issued for at least portions of the area with later
forecast packages.

Arctic high pressure will build strongly across the region Thu
with its center passing to our S Fri and then offshore Sat and
Sun. Southerly return flow will bring gradually higher temps and
humidity levels during this time. A cold front will approach
Sun night and may bring some showers, but otherwise it will be
dry Thu through Sun.

Highs will be in the upper 30s to lower 40s Wed and around 40
Thu. High temps should rebound into the 50s Fri and Sat and 60s
Sun. Lows will be mainly in the teens Wed night to around 20
along the coast with strong cold air advection. It will likely
not be quite as cold Thu night, but some locations could again
sneak down into the teens with strong radiational cooling. Lows
will then trend from upper 20s and lower 30s Fri night to 40s by
Sun night.


As of 06Z...Low cloudiness entering parts of Pender County but not
expected to get near ILM overnight. The remainder of the area will
see clear skies and light N to NE winds through the period.

Extended Outlook...Rain/MVFR/IFR/with a slight chance for
wintry precipitation late Wed, otherwise VFR.


As of 1034 PM Sunday...SCA replaced with an `Exercise Caution`
headline, for 15-20 KT winds and 4-5 foot seas offshore for the
overnight period. No other changes at this time.

As of 728 PM Sunday...Advisory conditions prevail with N wind
gusts to 25 KT and 6 foot seas offshore, so will allow the SCA
in place, to continue on this evening. As winds back to NW
overnight, sea heights should drop 1 - 1.5 ft, allowing the SCA
to expire later tonight.

As of 300 PM Sunday...High pressure remains north of the area,
building down the coast tonight and Mon. Northeast flow this
afternoon and overnight will gradually weaken as the surface
pressure gradient relaxes. Speeds currently around 20 kt will drop
to 15 to 20 kt overnight and the winds will back to a more northerly
direction. The combination of the wind shift and the decrease in
speeds should bring about an end to the already marginal small craft
advisory. In fact AMZ254 will probably drop below advisory
conditions prior to the current end time of midnight. Elongated
ridge axis remains west of the waters Mon with northerly flow
continuing to decrease and possibly becoming northwest as the period
ends. Seas 4 to 6 ft into the evening drop to 3 to 5 ft overnight
and will run 2 to 4 ft Mon.

As of 300 PM Sunday...High pressure extending down into the Carolinas
will maintain a light northerly flow through much of the period.
Models have been showing a possible area of low pressure
developing to the east of the waters late Tues into early Wed
which may sharpen the gradient and enhance the northerly flow,
but for now, will maintain northerly flow 10 kt or less
becoming more variable late Tues into Tues night as high
pressure weakens. Seas will remain 2 to 4 ft.

As of 300 PM Sunday...Small Craft Advisory conditions likely to
develop late Wed into Thu. Still unclear as to the exact
location and strength of developing coastal low. However,
magnitude of cold and dry advection will result in a period of
higher winds and seas through the first half of the period. Wind
speeds will likely peak in the 20 to 25 kt range with higher
gusts Wed night. The direction will be NW Wed and then slightly
veer to NNW Wed night into Thu morning. Seas will peak in the 5
to 9 ft range Wed night and Thu morning.

Winds will decrease to 10 to 15 kt by Thu afternoon and then
hold around 10 kt Thu night and Fri. The direction will back to
NW during Thu, W Fri morning and to SW Fri afternoon. Seas will
subside to 4 to 5 ft Thu afternoon with 2 to 4 ft seas generally
expected Thu night and Fri.





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