Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 170828
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
328 AM EST Mon Feb 17 2020

.SYNOPSIS...
Weak low pressure situated just off the coast will bring rain
and drizzle to the area through early Monday. Brief high
pressure Monday and Monday night will give way to more rain
Tuesday through early Wednesday as a frontal system crosses the
region. Rain chances hang around through Thursday as low
pressure develops to the south. Colder and drier air will
overspread the area late week into the weekend as cold high
pressure influences weather across the Carolinas..

&&

.NEAR TERM /THROUGH TUESDAY/...
Weak sfc low will move northeast along the coastal trof/front,
located just offshore from the Carolina Coasts. The Low will be
off Cape Hatteras by daybreak Mon. The pcpn will end across the
FA from west to east early this morning. In it`s wake, guidance
wants to paint fog and low stratus across the Carolinas, with
the threat for dense fog and VVs across inland locations. Models
indicate drier air infiltrating the mid and upper levels late
this morning thru tonight and best seen with the various levels
of water vapor imagery. As a result, any breaks in the low
cloud deck would allow insolation to peak thru which could push
max temps today hier. Will hold onto 60-65 for todays max temps.
For tonight included areas of fog but not all that convinced
for dense fog that some guidance is painting across the FA.

Flow aloft still to remain more or less zonal or basically low
amplified thruout this fcst period. This the reason why cold
frontal systems have been stalling west-east across the
Carolinas or just south of the FA and along the Gulf of Mexico
coastline. This next cold front, dropping south, will reach the
Carolinas late Tue. Weak mid-level s/w trofs or vorts to fire
up another round of weak sfc lows that will move along this
cold front. Pcpn will increase in coverage and intensity during
Tuesday morning and thru the afternoon. Pcpn amounts from now
thru early Tue evening only reach between one tenth to one-
quarter of an inch. Max temps for Tue may be a bit generous by
the models given cloudy skies and pcpn and as a result will use
lower 70s for Tue highs.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
Cold front will approach the area on Tuesday night as high
pressure builds over the central Plains. As the front
approaches, deep SW flow will develop over the Southeastern US
and advect moisture into the area. This will lead to a
continuation of shower activity through the evening. Showers
will be light overnight Tuesday and this will influence low
temperatures as a result, keeping most areas in the mid-50s.
Several models show the cold front passing the area during the
mid- to late-morning time frame. At the moment, have not backed
off the late-arrival solution. This leads to highs on Wednesday
approaching the 60-degree mark along the coast and mid-50s
inland with increasing shower activity likely during the
afternoon.

On Wednesday night, precip chances will dwindle as the cold
front brings drier air over the area. Will keep the possibility
of cloud cover and non-zero rain chances as westerly flow aloft
will cause isentropic life along the weak wedge of SFC high
pressure caused by advecting NE winds. Expect overnight lows
near 40.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Upper-level jet streak will prompt the development of a low pressure
system off the coast of GA during the day on Thursday. Clouds and
increasing PoPs from south to north across the area will limit
afternoon high temps. Late Thursday evening, three ingredients
become extremely important for P-Type Thursday night into Friday
morning. First, the high pressure building over the central US will
make a deep surge to the south and east. Current GFS and ECMWF model
runs show the high over Missouri with good agreement on strength and
center location. Second, the aforementioned low pressure system will
develop Thursday evening and quickly move to the north and east.
Strength of the initial low is similar in popular global models.
However, models differ on the location and propagation of this
system. The GFS currently shows the low developing, moving quickly
off to the NE, and tracking just to the S of Bermuda by Friday
morning. A secondary jet streak ahead of the longwave trough leads
to the development of a second low pressure system off the coast of
GA in the baroclinic zone along the SFC cold front and the Gulf
Stream. The ECMWF shows the low developing, zipping eastward, and
tracking NW of Bermuda by Friday morning. These subtle differences
lead to colder air within the ECMWF as the second low does not
develop in such a zonal and progressive pattern. The final piece of
the puzzle is moisture. The secondary low developing within the GFS
allows for moisture to hang around the area longer which could lead
to increased potential of wintry precip along the NC/SC coast on
Friday morning. However, with this being the warmer solution (and
cold air chasing exiting moisture), it would be a mix of rain and
snow transitioning to flurries. The ECMWF leads to colder air over
the Carolinas with its lone (slightly stronger) low pressure system,
but as the low exits, it has very little moisture to work with. For
now, will keep rain showers as this leans toward redevelopment of
low pressure after the first wave progresses and reflects a
climatological fight for cold air over the eastern Carolinas. Best-
case scenario, given current model trends is rain-snow mix
transitioning to flurries on Friday morning, but we would still need
a better push of cold air with a secondary low developing far enough
north to maintain some semblance of usable moisture. Hopefully the
trifecta comes together because this may be our only shot of seeing
those elusive ice crystals with March right around the corner.

High pressure builds in for cooler and drier air during the day on
Friday as clouds give way to clear skies. Below normal temperatures
on Friday before the air mass modifies on Saturday bringing us
closer to climo. Near normal conditions on Sunday as the high moves
overhead. Sunday night into Monday, the high moves offshore and
brings Gulf moisture back into the area ahead of the next cold
front. Expect warmer conditions, clouds, and a chance of rain on
Monday.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
MVFR/IFR conditions from low ceilings and reduced vsby from
fog will dominate overnight thru roughly 15Z. The inland
terminals may see bouts of LIFR conditions due to dense fog and
associated VVs. Leftover light rain or drizzle will lift away
from the Carolinas thru 08Z. Overall improvements to VFR
conditions likely by midday today as drier air temporarily
reaches and pushes across the Carolinas. The various low, mid
and upper level Water Vapor Imagery illustrates this nicely. The
main baroclinic zone is also shunted temporarily east and south
of the area with rain chances put on hold. The coastal
front/trof will remain offshore and east of the Carolinas this
period, resulting in N to NE winds. The sfc pg remains somewhat
relaxed with wind speeds around 5 kt inland terminals and up to
10 kt for the coastal terminals.

Extended Outlook...MVFR/IFR conditions expected Tue thru Thu
Night. This a result of weak waves of low pressure moving ENE
along a stalled front across the Carolinas. Improving to
dominate VFR late Thu night thru Fri as the stalled front
finally pushes south of the Carolinas followed by strong
Canadian high pressure.

&&

.MARINE...

Today thru Tuesday:
No Advisories or Warnings expected this period.

A coastal front/trof will remain situated just offshore and
parallel to the Carolina coastlines thruout this period. Sfc low
moving along this trof, will exit NE of the area during this
morning. Winds will generally resume a NNE-NE direction at 10-15
kt thru tonight. As the cold front drops south and closer to the
FA Tue, winds will become SE-S with the FA becoming temporarily
entrenched in the warm sector. Will see wind speeds increase to
around 15 kt. Significant seas this period will run 2 to 4 ft
with a few 5 footers off Cape Fear. A 1.5 to 2.5 foot swell at 8
to 9 second periods will dominate the seas spectrum this period.
Wind driven waves at 4 to 5 second periods will help round-off
the seas contribution.

Tue Night thru Fri:
Winds increasing during the day on Wednesday as a cold front
approaches the area. This will also bring a chance of showers to
the coastal waters, increasing throughout the day with higher
confidence in the NC coastal waters. Cold front pushes through
the area and high pressure builds in behind the front leading to
increased northeasterly wind 15-20 knots and gusts to 25-30
knots on Wednesday night. During the day on Thursday, low
pressure develops along the GA coastline and the pressure
gradient between this and the high to the north will cause winds
to increase to 20-30 knots with gusts up to 35 knots. Small
Craft conditions continue to look likely during this period with
increasing seas to 6-8 feet. Low begins to move away from the
coast during the day on Friday allowing winds to decrease
slightly. Conditions continue to improve through Saturday as
high pressure becomes centered over the area Saturday night.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.

&&

$$
SYNOPSIS...DCH
NEAR TERM...DCH
SHORT TERM...21
LONG TERM...21
AVIATION...DCH
MARINE...DCH/21



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