Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 171727

Area Forecast Discussion
National Weather Service Wilmington NC
128 PM EDT Sat Mar 17 2018

A dry cold front draped over South Carolina today will return
north as a warm front this morning and back south as a cold
front tonight, wavering across the Carolinas Sunday through
Monday. A strong area of low pressure is expected to develop
along this front and deepen as it moves east over the Carolinas
late Monday into Monday night, bringing a good chance for
showers and thunderstorms. A secondary area of low pressure
will develop over the Southeast moving up across the off shore
waters of the Carolinas through mid week as much colder air
funnels in from the north.


As of 1000 AM SATURDAY...Winds have begun to veer around to the
SW as front to the south begins to move back north as a warm
front. This will bring warm and moist air back over the local
area through this afternoon. An area of showers was just
reaching into Darlington and Marlboro and should diminish as it
heads east towards the coast this aftn. The main area of pcp
will remain over SC as a shortwave moves across the mainly zonal
flow to the south, but clouds will increase and stream across
the local forecast area through this afternoon. Sounding
profiles and time heights show a decent layer of moisture
between 4k and 14k ft this afternoon, but diminishing through
into early this evening. Therefore expect fewer clouds at the
end of the day. As winds come around to the SW, they will
increase and become gusty. Temps up near 55 to 60 late this
morning will be hampered by clouds and some showers, but WAA
should drive temps up near 70 along the northern tier of
counties (Robeson, Bladen, and Pender) and mid 70s along the
southern tier (Georgetown and Williamsburg).

The models are indicating this boundary will lift well north of
the area by this afternoon, but a low develops along the front
as a potent shortwave drives the boundary back south through
Sunday morning. The best chc of pcp tonight will be over NC
where better upper level support exists, but a low chc will
exist along the actual front as it drops south into early Sun
morning. Lows overnight will fall into the upper 40s to the
mid 50s to the south.


As of 330 AM Saturday...Somewhat of a noisy wx pattern of
features aloft and at the sfc across the U.S. during this short
term period of Sunday and Monday. What`s interesting is the
models are somewhat similar with one another with this noisy
pattern. The strength and positioning of these features are
what`s different amongst the models.

For Sunday, a mid-level s/w trof will track ESE across the FA
and off the coast. It will help drive a sfc cold front across
and south of the ILM CWA by late Sun afternoon b4 temporarily
stalling. Very limited moisture thru the atm column Sun
especially with a WNW downslope trajectory in the wind fields
aloft which generally scours moisture out. In essence, could see
widely scattered showers early Sun morning, otherwise looking
at an overall dry Sun with variable amounts of clouds. Temps
will run 5 to 10 degrees below normal if this front is able to
clean push across and south of the FA followed by some decent

For Mon thru Mon night, a couple mid-level s/w trofs with
Pacific Ocean and Rocky Mountain source regions tapped, are
both progged to push eastward and off the SE U.S. Coast. The 1st
will occur during Mon whereby it is able to lift the stalled
front northward as a warm front, taking it across the ILM CWA
late Mon aftn into Mon night. Here, models are having difficulty
with the intensification and location of this deepening sfc
low. Models should push closer to a uniform decision within the
next 2 model runs. At the tail end of this period, some decent
CAA is progged to push across the FA as the deepening sfc low
drives off the VA Capes. Moisture will likely be thinned out
enough and thus have kept any frozen or freezing pcpn out of
the fcst. Will still need to monitor partial thickness schemes
as next week approaches.


As of 300 PM Friday...Both the GFS and ECMWF develop another
cold and deep trough across the eastern U.S. by the end of next
week. The particulars of how we get that trough here are
different enough to produce sensible weather differences across
the Carolinas Monday through Tuesday.

A well-defined shortwave will move east across the Ozarks
Tuesday. The GFS shows enough ridging off the East Coast to
deflect this feature into Indiana/Ohio Tuesday, while the
flatter flow shown on the ECMWF allows the shortwave to move
into Virginia. Surface high pressure off the East Coast should
be lifting a warm front northward along the South Carolina
coast. On the ECMWF, the shortwave is close enough
geographically to the front to induce surface low pressure to
develop along the front. This scenario would lead to better rain
chances here on Monday, plus cooler temperatures with a slower
northward progression of the front.

Strong upper level northwesterly winds across the Rockies and
Plains will carve out an increasingly deep trough across the
lower Mississippi Valley Monday night into Tuesday. Surface low
pressure should intensify across the southern Appalachians in
response to this deepening trough, and the warm front should
lift northward through North Carolina allowing us one full day
in the warm sector Tuesday. Highs should reach well into the
70s Tuesday with breezy SW winds, along with waves of showers
and thunderstorms possible. SPC`s day 4 (Monday) severe weather
outlook includes a risk area across GA/TN/AL, and we`ll monitor
for the potential for strong storms here as this system
propagates into the Carolinas Monday night into Tuesday.

Tuesday night the strong surface low inland should move eastward
and off the Virginia coast. The trailing cold front will move
through our area with colder air building in on northwesterly
winds. Cold air aloft with the trough won`t allow for quick
clearing, and it`s possible we`ll maintain a cloudy/showery
pattern through Wednesday, along with much chillier
temperatures. Once the upper trough clears offshore Thursday we
should dry out, but may also have to deal (yet again) with
potential freezing temperatures as the surface high builds in
from the west. For now I`ve forecast lows as cold as the mid 30s
across much of our area for Thursday night, but with light
nighttime winds it`s quite likely there will be some areas below
32 degrees given this pattern.


As of 17Z...The front is expected to wave northward today with
increasing southwest flow. Some precip will try to slide into the
area this, but timing and amounts are quite uncertain. Likewise,
ceilings are likely to lower, again with uncertainty with respect to
timing and height. The models are hinting at sea fog/stratus for the
Myrtles but will reevaluate with next set of model runs. Sunday,
front drops south again with north winds returning and predominately
IFR conditions.

Extended outlook...Periods of MVFR Sunday through Wednesday.


As of 1000 AM Saturday...Front to the south has begun its
migration north again. This will shift winds around from the
E-SE to the SW through early this afternoon. As the boundary
shifts northward the winds will become southwest at 10 to 20
knots and the seas of 3 to 4 feet will increase to 3 to 5 feet.
A small craft exercise caution may be needed by this evening
evening and a Small Craft Advisory may be needed late tonight.

As of 330 AM Saturday...Of the 2 days, Sunday will be the
better of the 2 for venturing into the local Atlantic waters.
Sun starts off with a CFP from north to south b4 finally
stalling near the mouth of the Savannah River Sun evening. Weak
high pressure, dry conditions, and onshore flow in the wake of
the CFP on tap for Sun and Sun evening. Models quickly swing for
the worst conditions of the 2 day short term period as the
stalled front returns north as a warm front. And, a sfc low
on the front across the lower mid-section of the U.S. , is
progged to catapult itself to the Eastern Carolinas by Late Mon
night/ Tue Morning. It does intensify to sub 1000mb and further
tightens the sfc pg across the local waters. Looking at wind
speeds likely surpassing SCA thresholds and will have to monitor
for possible Gale Conditions by Tue. Significant seas will be at
a temporary lull Sun with mainly 3 to 5 second period NE-E wind
waves dominating. For Mon into Tue, wind waves will again
dominate in the 4 to 7 second period range, but their size will
surpass SCEC and even SCA thresholds. If Gales come to be, will
have to re-calculate the sig, seas. As for pcpn, looking at
liquid RW- with isolated thunder possible aided by mid-level s/w
trof energy as well in conjunction with sfc features.

As of 300 PM Friday...It will be a stormy start to next week
with a couple areas of low pressure expected to affect the
weather across the Carolinas. The first low is expected to
develop along a warm front moving north along the South Carolina
coast late
Monday. This low will slip offshore Monday night. A
second much stronger area of low pressure is expected to develop
inland Tuesday, drawing the warm front north of our area and
allowing breezy southwesterly winds to develop. As this low
moves offshore Tuesday night it will push the front back through
the area as a cold front, with colder northwesterly winds
expected to develop for Wednesday. Given this pattern, there is
increasing likelihood we`ll need a Small Craft Advisory for
Tuesday and Tuesday night for winds and seas.





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