Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 211945

Area Forecast Discussion
National Weather Service Wilmington NC
345 PM EDT Sat Apr 21 2018

Canadian high pressure will continue to extend into the
Carolinas as it migrates slowly east off the Mid-Atlantic coast
through Sunday. Slow moving low pressure will cross the
Southeastern U.S. Monday through Wednesday, bringing widespread
rainfall with continued below-normal temperatures. Another
system may affect the Carolinas Thursday into Friday.


As of 300 PM Saturday...A weak 500 mb ridge will move across the
area tonight and then offshore Sunday. An upper low dropping
southeast across Kansas will make it as far east as Arkansas by
Sunday afternoon. Developing southerly flow in the mid and upper
levels ahead of the upper low should begin to increase cloud cover
across the Carolinas Sunday, with veering low level winds even
developing a bit of stratocumulus beneath the upper level moisture
plume during the day.

A blossoming area of isentropic lift ongoing now across southern
Georgia is developing quite a canopy of mid-level clouds between
Charleston, SC and Jacksonville, FL. While a little of this moisture
may sneak across the Santee River overnight, our skies should remain
mainly clear with good radiational cooling expected. The only
exception to this will be within a few miles of the beaches where
steady onshore winds may prevent a radiational inversion from
developing until late tonight, if at all. For this reason I`ve tried
to show a large range in forecast lows as you move inland: 53 at
MYR, 50 at CRE, and 46 at FLO. The coldest temperatures tonight
should be across interior SE North Carolina where lower 40s are
expected in the normal cold spots.

Despite winds just above the surface veering more southerly during
the day Sunday, warm advection goes into lift leading to nearly
steady 850 mb temps. This means highs Sunday shouldn`t be
appreciably different from today: low 70s inland and mid-upper 60s
near the coast. Rain chances should hold off until sunset across the
SC Pee Dee region.


As of 300 PM Saturday...A complex weather pattern will unfold
during the short term period as low pressure, progged to be
near/just E of the MS valley during Monday, promotes strong
onshore low-level flow and Theta-E advection. As the upper low
drifts ENE across TN and into KY the pattern becomes favorable
for strong upward vertical velocities. The upward motion will be
enhanced by the increasingly divergent flow aloft, and the
convergent flow expected to be present in the low levels. As a
result, widespread areas across the ILM CWA may receive 1-3
inches of rainfall. Available instability for thunderstorms is
on the low side however strong lift supports carrying isolated
thunderstorms in the least. Best chance of rain will occur
Monday for southwestern zones, and Monday evening for the
remaining areas. Favored a blend of MAV/MET/ECE temperatures all
periods. Breezy conditions expected to develop during Monday,
especially along the coast. Will have to watch for potential
coastal flooding as well each high tide Monday into Monday night
given the onshore fetch.


As of 300 PM Saturday...A low pressure system will track off to
the NE Tues into Wed. The sfc low will track closer to the
coastline while the upper low will move northeast from TN toward
the Ohio Valley. As this closed upper low lifts north, another
shortwave will rotate down toward the Southern Appalachians by
Thurs. Overall, this system remains quite complex, but looks
like the heavier rain will move north leaving clouds but some
drier air wrapping through mid week. The next shortwave should
dig down and push a cold front through on Thurs, but does not
look like a big rainmaker. Therefore, expect breaks in the
clouds and some clearing late Tues into Wed with increased
clouds and potential for pcp again Thurs. Another system will
follow in this progressive flow by Fri into Sat, although the
GFS keeps most of the weather with this system north of our
local forecast area, while the ECMWF remains more pessimistic
heading into next weekend. Overall a good amount of clouds and
and not much QPF expected through the week. Temps have been
trending warmer but remaining near normals through much of the


As of 18Z...VFR conditions expected over the next 24 hours.
Easterly winds will reach 12 knots along the coast today, and
perhaps again late Sunday morning.

Extended outlook...Rain Monday and Tuesday could bring periods
of MVFR/IFR conditions in low ceilings and visibility. The worst
conditions are expected Monday night.


As of 300 PM Saturday...A ridge of high pressure extending from the
Great Lakes to just off the Virginia coast is maintaining an
easterly wind across the area. The high will move very little over
the next 24 hours as low pressure develops across Louisiana and
Arkansas, and this should maintain the easterly wind through Sunday.
Wind speeds should average 10-15 knots, perhaps a bit stronger by
late Sunday afternoon.

Buoys are currently reporting wave heights of 2-3 feet across the
coastal waters with the Frying Pan Shoals buoy offshore now up to 4
feet. Dominant wave period has shortened to around 5 seconds with a
second peak at 8-9 seconds indicating local wind chop is becoming
more dominant. Waves of 4 feet should become more common Sunday
afternoon south of Cape Fear.

As of 300 PM Saturday...Marine conditions will become hazardous
during the short term. High pressure off New England during
Monday with low pressure along the MS valley will create a
strong onshore fetch with Small Craft thresholds likely. Plan
to raise the advisory with the afternoon Coastal Waters
Forecast. The strong winds will continue into Monday night,
and it`s possible a period of Gales could occur. However,
confidence is not high enough to warrant a Gale Watch at this
time. The onshore fetch will allow for seas to get above Small
Craft thresholds by daybreak Monday, and to exceed 10 ft when
winds are strongest later in the day Monday into the evening.
Numerous showers and isolated thunderstorms are expected,
more-so across the southern waters initially, and all waters
by Monday evening.

As of 300 PM Saturday...Complex low pressure system will track
NE parallel and near to the Carolina/VA coast Tues into Wed. A
strong onshore flow will persist into Tues , but winds will
diminish as they shift around from on shore to off shore by Wed
on the back end of the low as it lifts off to the northeast.
Another system will follow behind this one, dragging a cold
through on Thurs. Therefore expect off shore flow to continue
through much fo the period.

Overall, expect seas to subside through the period from a peak
Tues morning, above 10 ft in outer waters. The on shore flow
will shift around to the off shore and decrease with seas down
below SCA thresholds by Wed morning and continuing to lower to 2
to 4 ft by Thurs morning.





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