Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 180440

Area Forecast Discussion
National Weather Service Wilmington NC
1240 AM EDT Sun Mar 18 2018

Mild temperatures will prevail tonight ahead of an
approaching cold front, that will cross the coast early Sunday.
Lingering clouds and slightly cooler temperatures will be
featured on Sunday. A warming trend can be expected early next
week as a storm system approaches. Periods of rain and showers
Monday night through Wednesday, may transition to light snow
Wednesday night before drier air sets in Thursday. Accumulations are
not expected because of the relatively warmer ground. A low pressure
system will approach the coast next weekend.


As of 1000 PM Saturday...Concern overnight involves a potent
shortwave evident on WV imagery moving overhead the Appalachians,
and how its interaction with a surface cold front will impact
convection overnight.

Latest regional mosaic shows an area of strong to severe
thunderstorms cresting the TN/NC/SC mountains and moving quickly
to the ESE. This is in response to the aforementioned shortwave,
and Although SPC has dropped the SLGT risk to our north, the
MRGL risk has been expanded to include the extreme northern tier
of the CWA. While the potential exists for thunderstorms
overnight, it appears the severe risk is low due to the elevated
nature of instability. Latest RAP soundings show 600-1000 J/kg
of MUCape for parcels near 900mb, enough to sustain convection,
but a stable surface layer should preclude any of the strong
winds aloft from mixing down. However, there is a small area,
mostly from Lumberton to Wilmington, where the high-res guidance
suite, including the RAP, HRRR, NSSL WRF, and ARW, all paint
some convection moving across beneath the upper vort and along
the front. This is due to a ribbon of the slightly better
instability correlating with higher moisture content and
stronger forcing. Have increased POP to mid-chc northern tier
and schc along the SC/NC border, but again, the severe threat
looks minimal. Cannot rule out an elevated hailer, but the
primary threat will be briefly heavy rain and some lightning,
focused from about 2am near Lumberton, to 7am near Wilmington,
and then moving offshore.

A weak surface wave beneath the potent vort will exit offshore
very late tonight or early on Sunday, and this will act to pull
the cold front to the south. Behind this front temps will drop
quickly and some stratus will develop, but exactly where this
front settles will determine the sharp temperature gradient due
to much warmer (cooler) temperatures on the south (north) side.
Have tried to show this with upper 40s by daybreak Sunday far
northern tier, while remaining in the mid 50s near the South
Santee River. Relevant portion of previous discussion below:

As of 344 PM Saturday...Southwest winds will veer around to the
north behind front as it drops south through the area early Sun
morning. Any lingering chc of pcp through the morning will lead
to drying by Sun afternoon. Pcp water values up near 1.4 inches
ahead of the front will drop to near a half inch air mass
clears out in drier northerly flow as high pressure builds in.
Max temps on Sunday will be near 60 over SE NC, but will reach
closer to 70 in NE SC.


As of 344 PM Saturday...ECMWF/GFS both show an upper low across
the Central Plains Sunday night. The upper low is progged to
translate across the MS Valley during Monday evening. At the
surface, a cold front will be aligned south of the forecast area
at the onset. In the meantime, an area of isentropic lift and
increasing low-level theta-E advection will bring rainfall
chances back into the area Sunday night. Mentioned a slight
chance of thunderstorms as well with some elevated instability
present late Sunday night into Monday morning, primarily for SC
zones. By early Monday evening both GFS/ECMWF position a surface
low across TN with the warm front returning north across the
area with decent rainfall chances continuing. Included
thunderstorms during this time frame as stability decreases
across the area. The ECMWF tracks the low a little further
south, but given either solution our rainfall chances will be on
the high end across the forecast area. Blend of MAV/MET numbers
appears reasonable through the period. Would not be surprised
to see the convective risk areas shifted a little farther north
for Monday, but the bulk of the instability will likely stay
farther south.


As of 344 PM Saturday...Low pressure pulling off the coast will
bring a lull Tuesday, before another low develops and brings
periods of showers Tuesday night through Wednesday, changing
over to snow or a rain/snow mix Wednesday evening. Forecast low
temperatures and thermal profiles, depict a brief period of
frozen precipitation is possible across much of the area. Sharp mid-
level drying will end PCPN prior to daybreak Thursday. Significant
accumulations are not expected due to warmer ground, but a "Frost`
advisory, or `Freeze Warning` may be needed very early Thursday,
favored over interior SE NC, but could reach into parts of NE SC.
Did not include thunder this period because of stable/cooler low
levels, but elevated instability will exist to some degree. QPF Tue-
Wed night averages to 3/10" to 5/10".


As of 06 UTC...A frontal boundary stretches from south of KHSE to
south of KRDU and to a low pressure center near KHKY. As an upper
level shortwave moves across this boundary overnight the frontal
boundary will shift again to south of KMYR and KFLO taf sites.
Elevated convection is possible but expected farther north of KLBT
and KILM and the South Carolina TAF sites are expected to remain
precipiation free overnight.

As the frontal boundary shifts south a few hours of IFR ceilings is
expected mainly after 09 UTC and clearing by 13 UTC as there will be
drying aloft boundary layer mixing during the morning.

Extended outlook...Periods of MVFR Sunday through Wednesday. Chances
for convection increasing Monday through Thursday.


As of 1000 PM Saturday...Front to the north will waver in the
vicinity until a shortwave and weak low pressure move along it
and offshore by the morning. This will drag the front southward
and turn winds to the N/NW. However, this is not likely to occur
until first thing Sunday, and most of the local waters will
remain entrenched in gusty SW winds of 15-20 kts through the
overnight, persisting seas at 3-5 ft. Relevant portion of
previous discussion below:

As of 344 PM Saturday...Winds will veer around toward daybreak
quite rapidly to the W-NW and then N, with speeds increasing
after a brief reprieve back to 10-15 kts. Seas will basically be
in the 2 to 4 ft range, but expect a few 5 fters in the outer
waters off of Cape Fear heading out toward Frying Pan Shoals.
Looks like seas should remain below any criteria for SCEC or

As of 344 PM Saturday...Weak high pressure across eastern NC at
the  beginning of the period will shift eastward Monday
morning. A stalled front south of the waters will begin to lift
north as another area of low pressure takes shape across the MS
Valley. The initial easterly wind will veer to a southeasterly
direction Monday morning. Additional veering is expected as low
pressure moves across NC Monday night. Thus a stronger southwest
fetch will develop with Small Craft Advisory conditions
possible overnight Monday. Seas will be highest in the southwest
fetch late Monday night.

As of 344 PM Saturday...This is shaping up to be a difficult
marine period, as a series of strong low pressure systems impact
the coast. Gusty SW winds 20-25 KT Tuesday and Tuesday night,
will shift to north equally strong, if not stronger Wednesday
as N and NW winds kick up in a cold air surge. Gusts to near
Gale force are not out of the question Wednesday over the outer
waters, with current numerical wave guidance at FPSN7 assigning 7
feet Wednesday. Very cold temperatures will greet mariners early
Thursday, in a moderate, but biting, offshore wind.





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