Area Forecast Discussion
Issued by NWS Wilmington, NC-- Highlight Changed Discussion --
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FXUS62 KILM 102318
Area Forecast Discussion
National Weather Service Wilmington NC
618 PM EST Sat Dec 10 2016
Arctic high pressure will maintain some of the coldest temperatures
of the season through tonight. A warming trend will begin Monday as
a coastal trough pushes ashore. A cold front will move into the area
Tuesday followed by a stronger cold front Wednesday night. As a
result, a chance of rain can be expected Sunday through Wednesday
with colder temperatures returning Thursday and Friday.
.NEAR TERM /THROUGH SUNDAY/...
-- Changed Discussion --As of 630 PM Saturday...Based on 6 PM observations I have
lowered forecast lows by a couple degrees in the Wilmington
area, with lesser changes at other cities. With such ideal
radiational cooling conditions expected for the next 6-8 hours
(calm surface winds, light winds at 1000 feet aloft, very dry
air, clear skies) I have ramped our local "radiational cooling"
tool up to its maximum setting. This local forecast editing
tool takes soil type into account and cuts up to 7 degrees off
model-blended low temperatures where peat/pocosin soils produce
localized cold spots on calm, clear nights like tonight. Parts
of the Angola Bay gameland in northern Pender County, NC could
conceivably dip to 17 or 18 degrees by 3:00 AM!
Discussion from 300 PM follows...
Expansive high pressure centered near the TN VLY is ridging
eastward across the Carolinas. This feature will continue to
push to the E/NE tonight beneath fast and increasingly zonal
mid-level flow. The combination of subtle warm advection off the
surface and the shifting high pressure overhead will lead to
rapid decoupling tonight, and winds will become nearly calm.
Calm winds and clear sky conditions allow for good radiational
cooling overnight, and mins are forecast to drop into the low to
mid 20s away from the immediate coast. This is more in line
with the cooler MAV numbers, as guidance tends to underestimate
the lows during the 2nd, better radiational night, after a cold
front. The exception to these colder temps will be very near the
coastline, where a developing coastal trough late will turn
winds more to the east, onshore, and may create some advecting
stratocu late. So while temps inland will drop to values very
close to last night, the coast should end up several degrees
warmer, a degree or two either side of 30.
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.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 230 PM Saturday...The moderating area of arctic high pressure
will shift off the coast during Sunday while a weak coastal trough
shifts onshore. The flow aloft will primarily be zonal through the
period helping move a cold front into the area during Monday.
Regarding moisture trends, expecting a sharp return of low-level
moisture by Sunday afternoon. Although clouds will be returning
during Sunday the level of saturation in the h7-h5 layer will be
lacking. Isentropic lift will increase Sunday afternoon allowing
rain chances to climb during the day, but more-so by Sunday night
into Monday. The lack of deep moisture will preclude any significant
QPF with this event with POPs carrying into Monday night.
Temperatures will be somewhat complicated during Sunday with the
coastal trough in the vicinity, at least until it becomes absorbed
in the synoptic flow. As a result, expecting high temperatures
around 50 across the far inland areas to the upper 50s at the coast
Sunday. Very little temperature variation heading into Sunday night
with ample cloud cover and weak return flow ahead of the cold front.
Lastly, high temperatures Monday could approach 70F across the
eastern two thirds of the forecast area in the relatively warm
southwest flow prior to frontal passage. Highs around 70 are
markedly higher than normal for this time of year (upper 50s).
.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 230 PM Saturday...Progressive west-east flow aloft will
continue across this part of the country with a fairly de-amplified
pattern overall. H5 heights will slowly increase over the area late
in the week with a trough to develop across the western United
States and ridge in the east. During Tuesday an area of weak low
pressure will develop off the NC coast with the first cold front
moving through by Tuesday. Ample low-level moisture will maintain
mostly cloudy skies through mid week with a continued chance of
light showers. A better surge will arrive Wednesday night into
Thursday as another area of cold high pressure ridges into the
Carolinas from the Midwest. Drier conditions will take hold with
below normal temperatures Thursday and Friday. Temperatures will
begin to recover this weekend as return flow develops with high
pressure shifting offshore.
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 18Z...High confidence in VFR through tonight, but
aviation conditions will deteriorate on Sunday.
High pressure ridging into the area from the west will move overhead
through tonight. This will continue SKC with light N/NW winds
becoming near calm after sunset. Despite a clear and calm night, fog
is not expected due to the very dry air, and VFR will persist into
daybreak. On Sunday, winds will begin to increase to 5-10 kts from
the east as a coastal trough develops offshore, creating slowly
lowering clouds. Attm any restrictions are progged to hold off until
just after this valid period, but at least SCT stratus/stratocu is
expected at all terminals on Sunday.
Extended Outlook...MVFR/-RA Sun evening with IFR Mon morning. VFR
developing Mon. Periods of MVFR/-RA Mon night through Wednesday with
IFR most likely during the morning hours. VFR Thursday.
-- Changed Discussion --NEAR TERM /THROUGH TONIGHT/...
As of 630 PM Saturday...No significant changes are needed to the
forecast as 5 and 6 PM observations match closely with the
previous forecast. Discussion from 300 PM follows...
High pressure ridging to the east will deflect just to the NW
of the local waters through tonight. SE of this high, a coastal
trough will begin to sharpen in the offshore waters before
drifting west on Sunday. The pressure gradient in the vicinity
of these features remains light through Sunday morning, so winds
will remain around 10 kts or less with slow veering from N to
ENE late. These light winds and lack of a significant swell will
keep wave heights just around 2 ft through the period.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 230 PM Saturday...Northeast flow around 10 knots Sunday
morning will gradually veer to the east, then a southeast direction
during Sunday afternoon with a coastal trough transitioning inland.
The pressure gradient will increase by early Sunday evening and
marginal Small Craft Advisory conditions are possible, mainly for the
Cape Fear waters. The Small Craft Advisory conditions should be
short-lived as the stronger pressure gradient shifts farther offshore
by Monday morning. The improved maritime weather will persist into
the afternoon with the overall flow veering to a west wind Monday
afternoon. Light offshore winds are likely by Monday night. Seas will
be highest as the winds peak in the wake of the coastal trough`s
passage inland late Sunday afternoon into early Monday morning.
Otherwise seas will be 4 ft or less Monday through Monday night.
LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 230 PM Saturday...Weak low pressure is expected to form in the
vicinity of the NC coast during Tuesday and push a weak cold front
across the waters. A stronger surge is expected Wednesday night into
Thursday with the passage of another front and sharp cold air
advection in its wake. Brisk northerly flow will occur as a result
during Thursday. Seas will range from around 4 ft on Tuesday and
lower to around 3 ft during Wednesday. Seas will build again
Wednesday night into Thursday in response to the surge.
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