Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 110225

Area Forecast Discussion
National Weather Service Wilmington NC
925 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.


As of 930 PM Saturday...9 PM temperatures were generally in the
upper 20s to lower 30s. IR satellite imagery suggests the
typical cold spots are already several degrees colder than
that. No changes are needed to the forecast with this late
evening update.

Surface high pressure over Virginia is ridging southward into
eastern North Carolina providing excellent radiational cooling.
The high will move offshore Sunday, but too late for any
meaningful return flow to develop tonight. Temperatures at the
offshore buoys will probably start to rise late tonight due to
warm advection developing, but our radiational inversion is too
well established on land for any effect to show up until after
sunrise Sunday. Discussion from 630 PM follows...

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!


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).


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.


As of 00Z...High pressure ridging into the area from the west will
move overhead tonight and off the coast Sunday. This will continue
SKC with nearly calm winds tonight. Despite a clear and calm night,
fog is not expected due to the very dry air in place, and VFR will
persist into the daytime hours Sunday. After 12Z, winds will begin
to increase to 5-10 kts from the east as a coastal trough develops
offshore, creating slowly lowering clouds. Latest guidance indicates
restrictions will 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.


As of 930 PM Saturday...High pressure centered over Virginia and
ridging down into eastern North Carolina is maintaining a
northerly wind across the waters. Observations show speeds
ranging from 5-10 kt near the coast to 10-15 knots in the 20-40
mile offshore zone. Seas have diminished to around 2 feet, and
little change is anticipated overnight.

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.

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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