Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 250200

Area Forecast Discussion
National Weather Service Wilmington NC
1000 PM EDT Sat Mar 24 2018

Low pressure moving along a front stalled to our south will
bring clouds and some light rain through Sunday. Strong high
pressure will build in from the northeast late Sunday, maintaining
cool weather through Tuesday. High pressure will shift offshore
on Wednesday with warm and dry weather to follow. Showers and
thunderstorms will cross the Carolinas ahead of a cold front on
Friday. Another shot of cool air will come Friday night into
Saturday as high pressure migrates across the Southeast.


As of 10 PM Saturday...Low-level water vapor imagery depicts
well the instability aloft approaching the Carolinas, ahead of a
potent impulse moving across IL/IN, where up to a foot of snow
has fallen, across the northern periphery of this energetic
short wave. Instability aloft will peak between 2 am and 6 am
over NE SC and SE NC, where a rumble of thunder is possible. The
energy waves aloft will track over a strengthening low-lvl
baroclinic boundary overnight. Rain will become widespread,
especially after midnight, as isentropic lift and vertical
circulations aloft increase. PWAT values peak either side of 9z
over the area, then shifts south and east, as the low pulls over
the sea. Most locations should receive between 1/2 and 1/4 inch
of rain tonight through Sunday morning.

As of 300 PM Saturday...Increasing moisture and a slight
increase in isentropic lift will help increase coverage of light
to moderate rain through the evening hours. Surface high
building down the coast and the passage of the surface low,
which will drag a cold front off the coast, will contribute to
rain expanding farther south overnight. There will be minimal
convergence along the cold front, so not looking for any
convection, but the nature of the front will generate light rain
behind the boundary. Light rain or drizzle could linger until
midday Sun or so.

Forecast soundings and cross sections show moisture/cloud cover
lingering through the day even though the low levels do start to dry
out. Surface high building down the coast leads to northeast flow
tomorrow with temperatures running well below climo.  How far below
climo is the question. NAM/WRF is a good bit cooler than the GFS and
normally would favor the cooler numbers in a wedge setup. Worried
that might see some peaks of sun late in the day. The rapidly
increasing late March sun angle would warm temps rather quickly
should it break out. Even with a thinning cloud deck some late day
warming may be inevitable. Thus have gone in between the cold NAM
and the warmer GFS but certainly potential for several degree errors
with high forecast tomorrow.


As of 300 PM Saturday...The mid level pattern will amplify
through the period evolving into an omega configuration. The
main feature for our region will be the sharp mid level ridging
across the Tennessee and Ohio Valley`s which will maintain a
sharp surface ridge into the area through the period. Any
lingering moisture in the form of cloud cover or light
rain/drizzle should be fading Sunday evening and skies should be
clearing by Monday morning. Regarding temperatures, the MET
guidance continues with the colder numbers and opted for what
seems to be a more reasonable solution of the MAV numbers. Lows
Monday morning should be in the middle to upper 30s with highs
later in the day in the middle to upper 50s.


As of 300 PM SATURDAY...The wedge of high pressure extending
down from the north will finally erode away through Tues as
ridge builds up the Southeast from the GOM. Light northeast flow
will shift around becoming more on shore through Tues and
eventually a southerly return flow will set up into Wednesday as
the high shifts off the coast. This will allow a warmer and
moister air mass to take hold of the Coastal Carolinas through
mid week. Temps reaching around 60 on Tues will be up around 70
by Wed and well into the 70s to near 80 by Thurs. Some high
level moisture will spill over the top of the ridge producing
some passing clouds which will filter out the sun at times
through mid week. The pcp water will increase up near an inch
Tues into Wed but the mid levels will remain very dry with
plenty of subsidence to keep any pcp out of the forecast Wed
into Thurs. As SW return flow increases late Thurs into Fri, the
pcp water will increase further, up near 1.5 inches Thurs night
into Fri as showers and possible thunderstorms increase across
the local forecast area ahead of a cold front. The GFS has sped
up the timing of the front, bringing it early Fri. This would
affect the potential for pcp on Thurs and max temp and
potential for any thunderstorms on Fri. Instead may see better
isentropic lift and chc of pcp behind the front into Fri aftn
with temps in the 60s. Dry and cool high pressure will build
in behind the cold front late Fri into Sat.


As of 00Z...High pressure centered well north of the area will
continue to nose in through the forecast period. The warm front will
be driven south as a fairly strong wedge sets up. Ceilings will
lower tonight to IFR, with light to moderate rain moving in after
midnight. Sunday, a classic wedge day with cloudy skies and slowly
improving ceilings. Northeast winds are forecast through the period.

Extended outlook...Sun afternoon IFR becoming MVFR. VFR Mon-


As of 10 PM Saturday...A front ends up laying across the
waters, near the NC/SC border before low heads southeast across
the area then offshore. Prior to the passage of the low,
northeast flow will develop across NC waters. Gradient becomes
more defined with speeds increasing to 15 to 20 kt late tonight.
Similar wind speeds are expected to develop across portions of
the SC waters prior to the passage of the low, but with
direction from the southwest. Seas will build overnight as
winds shift and speeds start to increase. Seas 3 to 4 ft are
likely by daybreak Sun with isolated 5 ft not out of the

Passage of the low and associated cold front will allow high
pressure to build in from the north. Gradient over the waters will
tighten up and speeds increase to 20 to 25 kt as early as mid-
morning Sun. Seas respond to increasing northeast surge and build
over 6 ft around midday, on their way to 8 ft and possibly higher as
the period ends. Will raise SCA for all waters starting at 15Z with
the headline running well beyond the end of the period.

As of 300 PM Saturday...Expect strong winds and high seas for
the entire period as surface high pressure anchored to the
northeast will be the primary driver of conditions across the
coastal waters. Sustained winds of 20-25 knots, leaning toward
the higher end of the range can be expected for several hours
Sunday evening. By later Monday and into Tuesday morning winds
will diminish slowly into a range of 15-20 knots. Seas
throughout the period will be 5-8 feet and possibly even higher
across the outermost waters. With good confidence, will go ahead
and raise/extend a small craft advisory through the day Monday.

As of 300 PM SATURDAY...NE winds will weaken as they shift
around becoming more on shore and variable on Tues and then
southerly by Wed into Thurs as high pressure shifts off the
Southeast coast. As winds ease, the seas will lower remaining
between 3 to 5 ft most of the period. A longer period, up to 16
second, NE swell will reach into the waters by Tues evening and
diminish slowly through Thurs as S-SW return flow increases.


MARINE...Small Craft Advisory from 11 AM Sunday to 8 PM EDT Monday for



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