Area Forecast Discussion
Issued by NWS Wilmington, NC-- Remove Highlighting --
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FXUS62 KILM 210025
Area Forecast Discussion
National Weather Service Wilmington NC
825 PM EDT Thu Apr 20 2017
The Bermuda High will extend west over the region through
early Sunday. A cold front will sag south into North Carolina
over the weekend. Low pressure will move slowly through the
Carolinas late Sunday through Monday night, possibly bringing
strong to severe thunderstorms and widespread rain. Low pressure
will slowly depart out of the area through Tuesday leaving
drier high pressure over the area through the middle of next
.NEAR TERM /THROUGH FRIDAY/...
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
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 /FRIDAY NIGHT 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 /00Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 00Z...VFR conditions basically thruout the 24 hr 00Z Taf
Issuance period. A low level jetstream, SW 20 to 30 kt, will
develop overnight, keeping sfc winds active from the SW-WSW.
These sfc winds will help prevent widespread ground fog from
developing, but still could see patchy MVFR fog in secluded
locations. Any leftover diurnally driven cu will dissipate
altogether early this evening, leaving only sct/bkn thin cirrus
moving overhead per latest ir sat imagery trends. Diurnal cu
will again develop by mid to late morning Fri and persist thru
the aftn. Could see isolated convection develop along a somewhat
pinned sea breeze, with it`s inland progression being limited
due to increasing winds thru the atm column from sfc thru 700mb.
Overall winds will be from the SW thru WSW tonight around 5 kt
once the sea breeze influence decays. Expect the sea breeze to
develop by midday with winds becoming SSW 10 to 15 kt with gusts
to 20 kt. Inland terminals will likely hold at WSW around 10 kt
by late Fri morning and persisting thru the aftn.
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 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
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.