Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 092333

Area Forecast Discussion
National Weather Service Wilmington NC
633 PM EST Fri Dec 9 2016

Arctic high pressure will bring in the coldest temperatures of
the season tonight. A warming trend will begin Sunday and
Monday. A cold front will approach from the Plains and will
move into the area Tuesday,remaining in the area through
Wednesday before a second stronger cold front will bring below
normal temperatures back to the area Thursday and Friday.


As of 630 PM Friday...After highs only in the mid 40s today
under full sunshine, the coldest night of the 2016-2017 winter
is unfolding. By daybreak lows should reach 21-25 for most areas
away from the barrier islands and immediate coast. There is
still some uncertainty about how strong the radiational
inversion will become tonight with 12-18 knot winds blowing
just off the surface, and rather extreme sensible heat flux
from the soil into the boundary layer due to relatively warm
soil temps.

Surface high pressure ridging across the Dakotas and into
Tennessee will build into the Carolinas overnight. 850 mb temps
of -4C to -6C could moderate a bit overnight not due to warm
advection, but due to a lowering of the subsidence inversion
aloft. All this spells crystal clear skies overnight.

The last time temperatures were as cold as we`re forecasting was
February 14, 2016 when lower 20s occurred in most locations.


As of 300 PM Friday...The germane weather streaming headline
this period reads `Frigid Sunday Morning, Chance of Rain Sunday
Night and Early Monday`. Arctic high pressure entrenched over
the region dawn Sunday will migrate offshore Sunday afternoon.
Height falls aloft co-joined with a tenacious surface wedge will
result in coastal trough formation just off the beaches. The
associated low-level convergence will set off a few showers as
the trough impinges the coast and coastal interior Sunday
afternoon and night. The best chance of rain being Sunday late
night as the trough sharpens and the moisture advection
accumulates. Warm air advection will raise temperatures well
above the threat of frozen pcpn, but the evaporative cooling
could keep maximums Sunday below guidance values.


AS OF 300 PM Friday...A comparison of the 500 mb flow between
the GFS and ECMWF both are vary similar with zonal west-
southwesterly flow over the southeast United States. In the
lower levels the models are showing return flow from the south
and southeast and the tail end of a coastal trough that had
developed the the south a few days earlier. In the larger
synoptic flow cold front from the plains is expect to move
across the forecast area late Monday night into early Tuesday.
Both the 12 UTC ECMWF and GFS are showing the cold front moving
off the coast and stalling to the south and east of the area.
Both are indicating that the surface low will now form a bit
farther off the coast. Uncertainty is high on the fronts final
location. There will be a chance of showers through Wednesday
with a lull expected Monday night. QPF values are not expected
to be extreme with this event.

A second cold front will push quickly through the forecast area
late Tuesday into Wednesday morning with another shot of colder
air later Thursday into Friday.


As of 00Z...High confidence in VFR through the valid period. High
pressure edging in from the west will become oriented overhead on
Saturday. Decent radiational cooling conditions overnight. May go
calm around 06Z. Northeast flow on Saturday, mainly below 10 kts.

Extended Outlook...Showers possible Mon-Wed. Otherwise VFR.


As of 630 PM Friday...Arctic high pressure ridging southeastward
will cover the Carolinas by late tonight. A relatively tight
pressure gradient ahead of this high will maintain northerly
winds at 15 to occasionally 18 knots this evening, diminishing
to 10-15 kt overnight. Seas currently 2-4 feet (highest near
Cape Fear) will diminish to 2-3 feet overnight.

As of 300 PM Friday...Main marine headline this weekend` Cold
but no Advisories expected Saturday, Deteriorating late Sunday`.
As high pressure nearly overhead Saturday migrates off the mid-
atlantic coast Sunday, a coastal trough will form near the
Carolinas coast. Due to increasing winds moreso east of the 20NM
zone, waves will build notably Sunday night to 4-6 feet and a
Small Craft Advisory is very possible then. This will be joined
by occasional rain showers reducing VSBY to 2-4 NM. In addition
to this, its possible the warm moist over the chilly inshore
waters could spur a bit of marine fog late Sunday night into
early Monday.

As of 300 PM Friday...South-southwest winds of 10 to 15 knots
will start long term marine forecast ahead of a cold front that
will push off the coast late Monday and stall near or just south
and east of the coastal waters on Tuesday. Winds to the west of
the will be from the west and west-northwest at this time winds
speeds are expected to remain below 20 knots. No small craft
condtions are expected.





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