Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 191712
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1212 PM EST Sun Nov 19 2017

.SYNOPSIS...
A strong cold front will move offshore early this morning, ending
the risk for showers and bringing very dry and much cooler
temperatures on brisk northwest winds. There is the potential
for a rather widespread frost away from the immediate coast
Monday night with some freezing temperatures possible inland. A
coastal trough and approaching cold front may bring some showers
late Tuesday and Tuesday night. Low pressure is expected to develop
in the eastern Gulf of Mexico mid week and may bring unsettled
weather to the eastern Carolinas Thursday and Friday as it moves
northeast. High pressure early next weekend will be followed by
the passage of a cold front next Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 920 AM Sunday...The cold front is just now moving
offshore with all of the showers with it. Clearing line is just
in its wake. I did remove all pops which were essentially coming
to an end anyway. Otherwise no changes. Previous discussion
follows:

A strong cold front had barreled through LBT and BBP and will
move across EYF and FLO in the 7 o`clock hour before heading
offshore between 9 and 10 am. Showers were racing NE ahead of
the front and had already ended W of I-95. The remaining light
showers will end with frontal passage with winds turning sharply
NW. Brisk NW winds and strong cold and dry advection will be
the rule behind the front.

Cold front rapidly approaching from the west is accompanied by
a line of showers, currently approaching the western edge of the
CWA. What was once an impressive, albeit low-topped, squall
line, has diminished into a broken area of showers. Some of this
is due to waning instability, but have also noted a separation
between convection the best baroclinicity/fgen forcing, both of
which will continue to occur and lead to even further weakening
of the convection through daybreak. Timing of the FROPA is well
matched by guidance, and expect the front and all showers to be
offshore around 9am. While a few locations may receive a brief
gusty shower with heavy rainfall, most areas will see just very
light showers and total qpf only a few hundredths of an inch.
Strong winds ahead of the front, noted on LTX VWP of 40 kt at
1kft, will continue strong gradient winds gusting to 30 mph
through FROPA however, veering to the NW behind the front.

Once the front crosses offshore, rapid cool and dry advection will
occur on gusty NW winds. This will create rapid erosion of the cloud
cover and cooling of low-level thermal fields through the day. This
will have the two pronged effect of leading to a sunny day, but with
temps struggling to warm despite the sunshine. In fact, highs today
are likely occurring right now, and although some diurnal warming is
forecast, do not expect temps to climb back to current values, and
instead afternoon-highs will be in the low to mid 60s.

Large area of high pressure will build eastward today and tonight
becoming positioned across the western Carolinas tonight. This
weakening of the gradient will allow north winds to relax, remaining
just a few kts above calm tonight. Cold advection rarely fully
decouples at night, so have left a few mph of wind through Monday
morning. This will prevent ideal radiational cooling, although a dry
column, cool 850mb temps, and light north winds will still permit
temps to crash into the low to mid 30s, but no freezing temperatures
are currently forecast. Soundings are quite dry at the surface and
winds will remain a few mph above calm, but have still introduced
patchy frost all zones away from the coast, except Robeson, Bladen,
and Inland Pender where the growing season has ended for 2017.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...High pressure will be overhead Mon and
the atmospheric column will be exceedingly dry with precipitable
water values less than two tenths of an inch. Expect bright
sunshine and very light winds Mon. 850 mb temps will be
increasing Mon, but after such a chilly start, the environment
should only support highs in the mid and upper 50s. Dewpoints
will be in the 20s for most of the day and this will result in
minimum relative humidity values as low as 25 to 30 percent Mon
afternoon.

The high will move offshore Mon night and Tue and an offshore
coastal trough is expected to develop. This trough should then
migrate W and may get rather close to the coast Tue night before
weak low pressure develops offshore of the Southeast Coast and
lifts NE. This weak offshore low will be lifting N of our
latitude Wed morning. At the surface, Canadian high pressure
will build SE and its expansive center should reach the
Mississippi Valley by the end of the period. However, aloft, a
very deep trough will be carving out which will lead to the
development of low pressure in the eastern Gulf of Mexico later
in the week.

The forecast gets a little murky later Tue and Tue night and it
is unclear how much precipitation will be realized across the
Forecast Area. Confidence is a little higher that coastal
communities would be most impacted by scattered showers given
their proximity to the aforementioned coastal trough. The GFS,
and to a lesser extent, the Euro model, are showing several
weak perturbations embedded in deep SW flow lifting across the
area. These weak features may be able to generate showers
further inland as well. Also, as moisture is tapped from the
Gulf of Mexico, we will see precipitable water values climb to
just over 1 inch Tue night. Thus although confidence is lower
than it normally is for this portion of the forecast, will
include chance POPs throughout, but favor the coast.

We are expecting clouds to fill in, possibly as early as
overnight Mon in the form of higher clouds, but more likely
during the day Tue when thicker clouds should arrive, with
skies becoming mostly cloudy by/during Tue night. Cloud
development as early as overnight Mon could impact low temps.
At this time, we are forecasting lower to mid 30s across inland
areas with upper 30s to near 40 at the coast. This may lead to a
frosty night across many areas away from the immediate coast
with some locations dropping to freezing inland. Daytime highs
in the 60s are expected during this period with lows Tue night
in the upper 40s to lower 50s with perhaps some mid 40s well
inland.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 300 PM Saturday...A couple of short wave troughs in the
southern stream will have some impact on area weather in much of the
extended period though confidence is currently low in exactly what
those impacts will be due to model divergence.

The first upper trough may bring a few showers into Wed with a
cold front moving offshore by/during Wed morning. After this
fropa, the second upper trough could spawn low development along
the front offshore and bring rain to the area Thu into Fri.

For now, the forecast reflects slight chance pops Wed and for
Wed night into Fri. Temperatures will be near seasonal normals
Wed before falling back into the mid to upper 50s for Thu and
Fri. Slightly warmer temperatures are expected Sat with highs
in the upper 50s to lower 60s. SYNOPSIS...Mins will see a
similar trend falling from the mid to upper 40s Tue night to the
mid 30s to around 40 Thu night before rebounding to the 40s by
Sat night.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
As of 18Z...With the cold front now offshore, dry and stable air
is flooding across the eastern Carolinas. Gustiness in this
northwest wind will continue another couple of hours near the
coast before settling down below 10 knots. Surface winds should
decrease further tonight with VFR conditions continuing.

Extended Outlook...VFR conditions are expected Sunday through
Tuesday morning. MVFR conditions may develop in low clouds and
light rain Tuesday night through Wednesday morning, then MVFR
to IFR conditions are possible Thursday night into Friday in low
clouds, rain, and fog.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 920 AM Sunday...No changes to the coastal waters forecast
this morning. Previous discussion follows:

Cold front approaching from the west will
cross the waters this morning and exit the area late this afternoon.
This front is creating a pinched gradient locally, and winds across
the waters are presently from the SW at 20-25 kt with higher
gusts. These winds will persist through FROPA this morning, and
then shift rapidly to the NW while remaining at elevated speeds.
Along with the wind shift, scattered showers with isolated
higher and erratic winds are also likely through late morning.

Although winds will begin to ease this aftn as high pressure builds
in from the west, strong cool advection will maintain gusty winds
through the period, falling only to 15-20 kt from the north
late tonight. The ongoing SCA will remain unchanged, and is in
effect through 6pm for 20-25 kt of wind (SW early, NW late) and
seas 5-8 ft. As the winds shift to the offshore direction, wave
heights will fall to 4-5 ft this evening, and 3-5 ft tonight,
but a SCEC may be needed once conditions fall below SCA
thresholds.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...High pressure will be overhead Mon. As the
high shifts offshore Mon night and Tue, a developing offshore coastal
trough will develop and migrate toward the coast. Current thinking
is this trough may move into the coastal waters later Tue before
shifting back offshore Tue night. In fact, the models are showing
a weak offshore low developing on this trough late Tue night which
will lift N of our latitude Wed morning.

The strongest winds this period will be Mon morning, up to around
15 kt from the N. The wind direction will veer to NE Mon afternoon
with speeds decreasing to less than 10 kt late. Wind speeds Mon
night will be 10 kt or less, veering from E to ESE. light and
generally easterly. The wind direction Tue will be SE at speeds
of near 10 kt. The wind direction will back to the N later Tue
night, increasing to 10 to 15 kt by Wed morning. Seas will trend
lower into Tue, from 3 to 4 ft early Mon to 2 ft or less later
Mon afternoon through Tue morning. Seas should then tick about
a foot higher Tue afternoon and then back to 3 to 4 ft Tue night.

LONG TERM /WEDNESDAY THROUGH THURSDAY/...
As of 300 PM Saturday...A coastal trough should retreat back
offshore by Wed morning as high pressure advances across the
Ohio Valley and shifts our winds to a more north to northeast
direction. Light winds and slight seas are expected until Wed
night or Thu when NE winds of 15 to 20 kt could build seas to 4
to 5 ft with 6 footers possible at 20 NM.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory until 6 PM EST this evening for AMZ250-
     252-254-256.

&&

$$

SYNOPSIS...
NEAR TERM...RJD/JDW/SHK
SHORT TERM...RJD
LONG TERM...RAN
AVIATION...TRA


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