Area Forecast Discussion
Issued by NWS Wilmington, NC-- Highlight Changed Discussion --
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FXUS62 KILM 210542
Area Forecast Discussion
National Weather Service Wilmington NC
142 AM EDT Fri Apr 21 2017
Bermuda High pressure will extend west across the region
through early Sunday. A cold front will sag south into North
Carolina over the weekend . Low pressure will develop on this
front and will further intensify as it slowly drops to the
southeast through the Carolinas late Sunday through late
Monday. Strong to severe thunderstorms and widespread rain
will accompany this slow moving low pressure system. The low
will slowly depart out of the area through Tuesday leaving drier
high pressure ridging across the area through the middle of
.NEAR TERM /THROUGH TODAY/...
As of 830 PM Thursday...Low amplitude ridge axis aloft and
across the area this evening, will slide eastward and off the
coast by early Friday. This will allow thin cirrus clouds to
push across the ILM CWA overnight thru Friday. A low level jet
and a slow tightening of the sfc pg, will both combine to keep
an active sfc SW-WSW winds across the ILM CWA overnight and
continuing thru daylight Friday. This will help prevent any fog
issues like what occurred Wed night/Thu morning. Could see
isolated pockets of fog but at this time not enough coverage to
mention in the fcst. Low temps tonight will remain elevated and
only drop into the low to mid 60s, which is nearly a good 10
degrees above the normal lows for this time of the year. The
same goes with Friday max temps, running up to 10 degrees above
As of 300 PM Thursday...The weather pattern is reminiscent of
summer with surface high pressure out near Bermuda and
sufficient heat and moisture for an expansive cumulus field and
a well-defined seabreeze. Dry air aloft has thwarted the
potential for showers so far, although I`ll maintain a 20-PoP
through about 6 PM in the Cape Fear region for an isolated
shower that still may develop. Mid and upper level winds are
from the west, so any showers that do develop will be pushed
back across the seabreeze front toward the ocean.
Clouds should largely dissipate with the loss of heating this
evening. With the high off the coast a modest southwesterly low
level jet should develop with wind speeds at 1000 feet AGL
increasing to 25-30 knots. This frisky wind should help keep the
nocturnal inversion from becoming too deep, and my forecast
lows are near the warmer GFS MOS numbers: 65-68 along the coast
and 62-65 inland.
It`s easy to lose sight of the fact those lows are a good 12-15
degrees above normal for this time of the year. The month of
April has averaged 3-4 degrees above normal so far with
departures over the past week in the +5 to +7 degree range.
Heat increases further Friday with highs expected to reach the
upper 80s for virtually all areas more than 15 miles from the
coast. Conditions aloft will be even drier than today, and with
no upper level support I am keeping the forecast dry.
.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Biggest challenge this period involves a
southward drifting cold front which will waver to the north before
dropping towards the area late Saturday night. Broad mid-level
ridging and offshore high pressure will dominate the synoptic flow
across the Southeast Friday night through Saturday, creating very
warm temperatures and minimal precip chances. Mins Friday night will
likely stay in the upper 60s on the coast, mid 60s inland, serving
as a launching pad for highs to climb into the mid 80s away from the
beaches on Saturday. A strong sea breeze on Saturday will keep the
coast cooler, around 80, with mid 70s on the coolest Brunswick
County coast. Isolated showers/tstms are possible Saturday aftn, but
with dry mid-levels and weak forcing, have capped POP at 20 inland.
The forecast becomes muddled Saturday night as a cold front to the
north tries to sink southward into the area. The guidance differs
greatly in this evolution, with the WRF pushing the front through
into SC by Sunday morning, the ECM keeping the front way to the
north, and the GFS somewhere in between. The WRF is clearly the
outlier, and is ignored for this forecast due to strong impeding
SW flow downstream of a deepening upper trough, suggesting the
front will struggle to drop south that quickly. A GFS/ECM blend
is then preferred which keeps the front just to our north, and
while a few showers are possible late in the period, most of the
convection should hold off until the extended. With the front
forecast to remain north of us Saturday night, warm mins are
again expected, dropping only into the mid 60s.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 300 PM Thursday...Bermuda high will be losing its grip on
the Carolinas as low pressure system moves in from the west on
Sunday. Both the GFS and ECMWF show the low center moving east
almost directly along the NC/SC border reaching into the local
forecast area right around sunset Sun evening. This will
maintain a deep warm and moist southerly return flow with temps
into the 80s and dewpoint temps in the mid 60s. Initially expect
a fair amount of sunshine early Sunday which should lead to
some localized cu and shwr development associated with the sea
breeze front as any large scale forcing will be lacking. Once
the low moves east, expect increasing clouds and chc of pcp.
With the track of the low possibly bisecting the area, there
could be potential for severe weather over southern portions
mainly east and south of low center, but also could see more in
the way of isentropic lift and rain to the north. The loss of
heating may diminish the chc of severe convection into the
overnight hours but the best upper level support will head east
toward the coast by Mon morning. Overall expect fairly
widespread coverage of pcp late Sun into Monday. The latest
model runs do show a more southern track for the low which
could produce more in the way of overrunning pcp for our local
area rather than thunderstorms, but that remains to be seen.
The sfc low center should be just over or near the Cape Fear
coast Mon morning, but the deep upper level trough will still be
west. The cutoff low center will track mainly south of the area
but the trough will extend up through the Carolinas. The low
will move east through the day on Mon and then will travel
slowly N to NE parallel to the coast. This will keep clouds and
rain chances in the forecast possibly through Tues. Should see
drier conditions by mid week as weak high pressure builds in
behind departing low.
Temps should be a good 10 degrees cooler on Monday in northerly
flow on the back end of the low. Clouds and rain will keep
smaller diurnal ranges with temps heading back toward normal
Tues into Wed as low slowly departs. Overnight lows will
probably be 55 to 60 most places. Temps should be back up into
the 80s by mid week with increasing sunshine.
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 00Z...High confidence in VFR conditions through the
period. Boundary layer winds will remain 5 to 10 kt overnight
due to 20 to 30 kt low level nocturnal jet. This will prevent
development of significant fog and the low levels are dry
enough that stratus is not a concern. Southwest flow will be on
the breezy side today with potential for gusts in excess of 20
kt, especially along the coast. Cannot rule out an isolated
afternoon shower but the chance a terminal would be impacted is
very low. Any diurnal clouds that develop will dissipate around
Extended outlook...MVFR/IFR conditions possible in showers and
TSTMS, mainly Sun through Mon. Otherwise VFR.
-- End Changed Discussion --
NEAR TERM /THROUGH FRIDAY/...
As of 830 PM Thursday...Once the sea breeze influence to the
winds decays later this evening, winds will become SW-WSW at 10
to 15 kt. A low level Southwesterly jet and a slow tightening of
the sfc pg will combine to influence wind speeds across the
local waters. This will result in SW winds at a solid 15 kt or
possibly a range from 10 to 20 kt. Will decide at press time.
Significant seas will run 2 to 4 ft with the 4 footers occurring
across the ILM NC Waters where winds in general will run hier
than the ILM SC Waters. An easterly pseudo swell at 7 to 8
second periods will dominate the seas spectrum this period.
As of 300 PM Thursday...High pressure anchored about halfway
between the North Carolina coast and Bermuda will maintain a
southwesterly wind across the area for the next 24 hours.
Although wind speeds are quite light today, a modest increase in
wind speeds is expected Friday as the pressure gradient
tightens in advance of an approaching cold front over the Ohio
Valley. Seas are generally around 2 feet inside 20 miles from
shore, the result of at least two sets of 7 to 8 second swells.
Seas should build by at least a foot if not a foot and a half by
Friday afternoon due to the developing winds.
SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...High pressure offshore and a slow moving
cold front to the north will keep SW winds entrenched across the
waters through the period. SW winds of 15-20 kts will be common
through Saturday, with a slow decrease in speed, especially
northern waters, Saturday night as the front sags towards the
area. Long period easterly swell from TD one will combine with
steepening 5-sec SW wind waves to produce seas of 3-5 ft.
LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 300 PM Thursday...A southerly flow up to 15 kts or so
will persist on Sun between Bermuda High pressure extending over
the local waters from the east and an approaching low pressure
system to the west. The persistent southerly push could drive
seas up from 3 to 5 ft to near SCA thresholds by late Sunday.
The low will move across the waters Sun night into Mon with a
sharp shift in wind direction to the N on the back end.
The center of the low should be just near or south of the Cape
Fear coast Mon morning. The winds may diminish and become quite
variable at this time before the low slowly moves east and north
through late Mon into Tues. This should allow seas to diminish
for a brief period Mon morning before a sharp rise in
northerly surge on the back end. Winds may increase up to 15 to
25 kts Mon into Mon night before diminishing through late Tues
as low tracks farther away. Seas may remain above SCA late Mon
into Tues, diminishing Tues night in a lighter northerly flow.