Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 290156
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
956 PM EDT Fri Apr 28 2017

.SYNOPSIS...
High pressure will extend across the area from offshore through
Sunday. Expect warm temperatures and isolated sea breeze
showers or storms, mainly Sunday. The next cold front will
bring a chance of showers and thunderstorms late Monday into
early Tuesday. High pressure will follow for the mid-week
period. Low pressure system may impact the region during
Thursday with a soaking rain.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 1000 PM Friday...It`s been fascinating watching the low
clouds along the coast on 11-3.9 micron satellite imagery this
evening. Low clouds from Myrtle Beach northward appear to
eroding along the south edge, but clouds in the Georgetown
vicinity are holding together a little better. Not even the HRRR
model is good enough to forecast the movement of such a small
mesoscale phenomenon, so I`ve attempted to manually extrapolate
the cloud movement northward in the forecast grids over the
next 4-6 hours as they spread inland but spare the immediate
Cape Fear coastline. No significant changes to forecast low
temperatures. Discussion from 630 PM follows...

An unbelievably humid airmass for this early in the year covers
the Carolinas. Dewpoints in the mid 70s are practically unheard
of in April, and even with nearshore ocean water temperatures
near record warm territory these dewpoints have generated areas
of sea stratus and even sea fog earlier along the GA and SC
coast.

Inland cumulus should die away fairly quickly this evening with
the loss of daytime heating. It`s a little more uncertain how
clouds will respond near the coast: very humid air streaming
onshore will experience frictional/speed convergence which
could maintain a very low stratocumulus deck affecting
Georgetown, Myrtle Beach, and Wilmington through the evening
hours. Precipitation appears unlikely overnight as the depth of
our moisture is very limited and will be capped off by warm and
very dry air aloft.

Lows tonight will run at least 15 degrees above normal for the
date with 69-74 expected, coolest inland.

Climate note: Wilmington`s low temperature so far today has been
74 degrees. Assuming we don`t drop below 74 between now and
midnight standard time (1 AM daylight time) this will establish
a new all-time record warm low temperature for the month of
April in Wilmington. Records extend back to the year 1874.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY NIGHT/...
Saturday and Sunday: The synoptic pattern will be dominated by deep
layered subtropical ridging with the region positioned just to the
west of the 850-500 hPa anticyclone. Modified forecast soundings for
both Saturday and Sunday show pronounced capping with only the far
interior west of I-95 becoming uncapped for about 1-2 hours with the
sea breeze. Given lower tropospheric moisture looks pretty meager
outside of the boundary layer, prefer to go with a dry forecast for
both days. Temperatures will remain above normal with highs ranging
form the lower 90s well inland to around 80 at the beaches. Lows
Sunday morning will range from the upper 60s inland to the lower 70s
at the beaches.

Monday: A cold front will approach from the west Monday as high
pressure shifts farther offshore and a powerful storm system moves
into the upper Mississippi Valley. Moisture return ahead of the
front looks solid with taps noted from off the Gulf of Mexico and
Atlantic. Although the upper low and the core of the strongest
forcing looks to pass well to the north, there will be enough to
support a broad swath of showers/tstms across the frontal zone. Pops
will be increased to 70% for most zones Monday night as the front
sweeps offshore. Highs will warm into the lower-mid 80s away from
the beaches Monday afternoon with lows Tuesday morning ranging from
the upper 50s well inland to the mid 60s at the beaches.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Surface and mid level ridge will weaken and drift east Mon,
allowing a cold front to approach from the W. Low pressure and
associated strong dynamics and upper level support will be well
dislocated from the Carolinas as a cold front moves across the
area Mon night. This suggests convection weakening as it moves
into the eastern Carolinas. Current timing brings the likelihood
for showers and thunderstorms later Mon and Mon night.

As the front moves off the coast Tue morning, high pressure
along the Gulf Coast will slide east and then offshore to our S
during Wed. This should bring a dry period. Deep low pressure
will move out of the mid south and Gulf coast states Wed,
lifting slowly to the NE. Its associated cold front will move
into the Southeast states Thu-Thu night, bringing the risk for
robust thunderstorms.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
As of 00Z Saturday...Low confidence forecast with cloud heights
along the coast over the next several hours as we transition
from day to night. Very rich low level moisture streaming
onshore has supported MVFR/IFR ceilings along the coast of the
Carolinas this afternoon. While the moisture will remain
overnight, the loss of daytime heating could cause an erosion
of this cloud cover -- but to what degree is unknown. The last
few visible satellite images show fairly solid low cloud cover
extending from Charleston and Georgetown which should move
northward along the coast now through 06Z. Forecasts are for IFR
ceilings to perhaps improve to MVFR temporarily in the MYR/CRE
area after 02Z, but confidence in low.

At least scattered low clouds below 1000 feet AGL will persist
all night even if ceilings do not develop. Models even suggest
after 06Z enough moisture will push inland that FLO and LBT
could see some scattered low clouds develop. VFR conditions
should develop after daybreak.

Extended outlook...Periods of IFR/MVFR conditions are possible
in showers and thunderstorms late Monday into early Tuesday.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1000 PM Friday...The seabreeze has died away leaving winds
mainly in the 10-13 knot range which should persist overnight.
No significant changes are needed to the forecast. Discussion
from 630 PM follows...

South winds across the coastal waters have been strongest
nearshore for the afternoon with the seabreeze. Farther offshore
winds are barely 10 knots at the Frying Pan Shoals buoy and the
Edisto buoy east of Charleston. Once the seabreeze dies away
expect a very warm and humid onshore flow to continue overnight.
Although we don`t expect true sea fog to develop, periods of
low stratus clouds and hazy visibilities in the 2-4 mile range
are possible.

SHORT TERM /SATURDAY THROUGH MONDAY/...
As of 300 PM Friday...Southerly wind regime will persist
through Monday as the region remains along the western flanks of
Atlantic high pressure centered well offshore. Speeds will
generally remain 10-15 kt through the period, except Sunday
Night into Monday where speeds increase to 15-20 kt and 20-25 kt
Monday night as low-level jetting and a tightening pressure
gradient settle in ahead of a cold front. Seas will slowly build
over the weekend, peaking 5-7 ft by Monday night ahead of the
cold front. A Small Craft Advisory could be needed as early as
Monday morning.

LONG TERM /TUESDAY THROUGH WEDNESDAY/...
As of 300 PM Friday...In the wake of the cold frontal passage
early Tuesday, offshore winds will slowly diminish. The offshore
trajectories will knock seas down and should drop below Small
Craft Advisory levels by Tuesday afternoon. There are no
concerns for Wednesday into Thursday.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...Coastal Flood Advisory until 2 AM EDT Saturday for NCZ107.
MARINE...None.

&&

$$

SYNOPSIS...99/CHS
NEAR TERM...TRA
SHORT TERM...99/CHS
LONG TERM...99/CHS
AVIATION...TRA



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