Area Forecast Discussion
Issued by NWS Wilmington, NC

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904
FXUS62 KILM 191902
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
302 PM EDT Thu Apr 19 2018

.SYNOPSIS...
A dry cold front will move off the coast this evening. Chilly
temperatures are expected tonight through Sunday as Canadian
high pressure builds into the Eastern U.S. Low pressure will
move slowly across the area Monday through Wednesday next week,
bringing rain back to the Carolinas.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 300 PM Thursday...A pair of shortwaves moving across the
Northeastern U.S. coast has induced surface low pressure to
develop southeast of Cape Cod. A cold front extending south from
this low is moving through the Carolinas now, and should sweep
off our portion of the coast between 5-8 PM. Strong westerly
winds in advance of this front have gusted as high as 39 mph in
Wilmington, 38 mph in Florence, and 37 mph in Marion, SC. As the
front moves through this evening, winds will shift to the north
with much drier and cooler air punching southward.

High pressure over Iowa will only slowly move eastward tonight
and Friday. Cold advection should drop 850 mb temps down to +4C
tonight, and +2 to +3C Friday afternoon. At the surface we`re
expecting lows tonight to range from 39-44, near a MOS
consensus. For users of the new "National Blend of Models" MOS,
it performed very poorly with nighttime lows (too warm) during
the last cold blast we had back on April 8th, so I`ve ignored
its output which has lows 42-46. Also during the last cold
blast, the GFS MOS ran much warmer than other guidance with
highs and did not verify well, so I`ve ignored its output for
Friday. Following the cooler NAM and ECMWF guidance for
tomorrow`s highs yields lower 60s in the Cape Fear area and the
Grand Strand beaches, mid 60s across Whiteville, Lumberton and
Marion, and upper 60s for Florence and Darlington. Temperatures
this month so far have run 1.5 to 2.5 degrees colder than
normal.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Weakly amplified mid-level pattern will
transition from 5h troughing at the start of the period to weak
shortwave ridging Sat and Sat night. Meanwhile, surface high over
the Great Lakes at the start of the period will drift southeast Fri
night and Sat, ending up over the Outer Banks Sat night. Northerly
flow will be maintained through the period, keeping temperatures
below to well below climo. On Sat most areas will end up with highs
below 70, after starting out with lows in the upper 30s to lower 40s
on the back on good radiational cooling. Sat night lows will be
similar to Fri night although slight increase in boundary layer
winds might help keep temps a bit warmer. Clouds let alone rainfall
seem like a stretch. Precipitable water remains under half an inch
through the period with forecast soundings suggesting the bulk of
any cloud cover will be above 25k ft late Sat and Sat night.
Forecast soundings continue to show a nice subsidence inversion in
place through the period, preventing upward motion.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 300 PM Thursday...Very large high, more typical of the cool
season, to be moving off the coast on Sunday. Meanwhile a cutoff
upper low (also normally a cool season feature) to be crossing the
Gulf States, leading to cyclogenesis. As often the case with a
cutoff, the timing is often uncertain and too fast in guidance. Much
of the cloudiness and rain expected to overspread the area Sunday
night into Monday may now be about 12 hours slower. Another change
from this time yesterday is that guidance is now suppressing the
highest rainfall amounts to our south. Given the strength of the
high to our north this seems plausible. Even so, the system will be
slow  moving and keep rain in the forecast through at least
Wednesday.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 18Z...A dry cold front will push through the region
today. Good southwest gradient ahead of the front. Winds will
shift to the west post frontal. Cold air advection will arrive
by mid to late afternoon, with winds continuing to back to the
west northwest. Tonight, cold air advection will continue with a
large diurnal swing in temperature. Too dry to support fog.
Friday, continued northwest flow with cooler temperatures.

Extended outlook...VFR through Sunday.  MVFR is possible at times
Monday through Tuesday morning with rain in the area.

&&

.MARINE...
NEAR TERM /THROUGH FRIDAY/...
As of 300 PM Thursday...A dry cold front extending from New Bern
to Elizabethtown, Lumberton, and Bennettsville, SC will move off
the coast between 5-8 PM, accompanied by a shift from westerly
to northerly winds. Wind gusts around 25 knots all afternoon
will continue behind the front, and should even increase late
this evening to around 30 knots as colder air punches south
across the Carolinas. High pressure across the Midwest will
slowly build eastward Friday, with our winds weakening and
veering northeasterly.

The strong west and southwest winds of the past 24 hours have
built an impressive wave set, particularly across the open
waters of Long Bay and along Frying Pan Shoals where the CORMP
Harbor buoy and the NDBC Frying Pan Shoals buoy have been
reporting 7 foot seas all day. Dominant wave periods of 6-7
seconds should allow a great deal of this wave energy to make
into shallower water nearshore, and I`ll continue the Small
Craft Advisory through the night and into Thursday morning.

SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Surface high northwest of the area Fri night
will gradually drift southeast Sat. The high ends up centered over
the Outer Banks Sat night. Flow will remain northerly Fri night into
Sat before slowly veering to east-northeast late Sat. Gradient
remains fairly static through the period with speeds mostly in the
10 to 15 kt range. Seas will be in the 2 to 3 ft range through the
period.

LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 300 PM Thursday...Onshore flow on Sunday the result of a
very large area of high pressure moving eastward but remaining
centered well north of the area. At the same time low pressure
will be developing over the Gulf States. This setup will
increasingly squeeze the gradient to where wind and seas both
reach advisory levels. Both entities will be very slow moving,
keeping advisory flags flying for the remainder of the period.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory until 9 AM EDT Friday for AMZ250-252-254-
     256.

&&

$$

SYNOPSIS...TRA
NEAR TERM...TRA
SHORT TERM...MBB
LONG TERM...III
AVIATION...DL



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