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Area Forecast Discussion
National Weather Service Wilmington NC
1246 PM EST Sat Dec 3 2016

High pressure will move offshore Sunday night. A complex storm
system will bring periods of heavy rainfall late Sunday through
Tuesday. Cool and dry high pressure will follow this system for
mid-week. A true Arctic front will cross early Friday, ushering
in the coldest air since last winter.


As of 1230 PM Saturday...Cirrus has increased just a bit faster
than anticipated. Visible satellite shows a thickening (but
still translucent) cirrus deck extending across most of South 
Carolina now. Still very few changes to the forecast are needed.
Discussion from 600 AM follows...

The low level flow will be from the N and NE. Satellite imagery 
shows considerable higher clouds racing across the southern CONUS. 
Model profiles show this moisture increasing above 15 kft today with 
mid level ceilings beginning to materialize tonight. Thus, sunshine
will be more filtered as compared to recent days. Given temps 
at 850 mb will only be in the single numbers and sunshine will 
be increasingly filtered, forecast highs are not expected to 
exceed the mid 50s. The clouds tonight should help to keep temps
from falling below the mid 30s to around 40.


As of 300 AM Saturday...Chilly high pressure will be centered just 
to our N Sunday. The high will move off the coast Sunday night. At 
the same time, a very wet southern stream system will be organizing 
along the Gulf Coast. Warm and moist air will override the cool 
airmass near the surface and isentropic lift will be on the 
increase. Clouds should be plentiful on Sunday. Moisture should be 
streaming N and E and it is possible light rain will break out 
during Sunday afternoon, especially across the Pee Dee and 
Interstate-95 corridor. A warm front is expected to develop to our S 
and along the southeast coast Sunday night. The lift associated with 
this feature is expected to increase the risk for rainfall and have 
increased POPs to categorical.

Monday and Monday night, strengthening low pressure is expected to 
move from the western Gulf Coast and across the mid south. A warm 
front will extend eastward from the low. Another area of low 
pressure may begin to develop along the offshore coastal front. A 
southwest low level jet of 50-60 kt will bring copious moisture up 
and over the front to our S. Precipitable water values will be near 
2 inches while the depth of moisture becomes very deep. Thus, will 
show POPs as high as categorical. Rainfall rates should increase 
given the increasing lift and moisture supply. Will add mention of 
heavy rain. The frontal system is expected to remain to our S and E 
through 12z Tue and so will keep any mention of thunderstorms 
offshore where instability should be highest. We are still expecting 
a soaking rain with amounts through Tue in the 1 to 2 inch range and 
as high as 3 inches.  

High temperatures will be below normal through the period, mainly in 
the lower to mid 50s Sunday and mid and upper 50s Monday. Low 
temperatures will be in the 40s Sunday night and mid 40s to mid 50s 
Monday night, highest at the coast.


As of 300 AM Saturday...An active pattern continues next week, and 
the extended will begin with a potentially high-QPF rain event. Low 
pressure developing along the Gulf Coast will move NE, with 
secondary re-development likely along the Carolinas Coasts. High 
pressure in place ahead of this feature will slowly erode to the NE, 
with strong isentropic lift in an environment with increasing PWAT 
driving periods of heavy rainfall Tuesday. While initially the 
precip characteristic will be stratiform, recent guidance has 
shifted the secondary low track just inland, which could allow for 
more dynamic/convective rainfall late Tuesday. This can be ironed 
out as we get closer to the event, and what is more certain is 
significant rainfall, with the GFS ensemble plume mean centering 
near 2 inches in the timeframe ending Tuesday night. 

A cold front trails this system Tuesday night and seasonably cool 
and dry weather is forecast Wed/Thu before a strong trough digs into 
the Great Lakes driving an arctic cold front through the Carolinas 
on Friday. Moisture return ahead of this feature may be limited, so 
showers along the front are currently forecast to be light early 
Friday. More noteworthy is the polar air mass behind this front, and 
850mb temps may approach -10C by the end of the period, signaling 
well below normal temperatures beginning Friday.


As of 18Z...Very good confidence VFR through the remainder of this 
afternoon and overnight. Ceilings will gradually lower from present 
mixed-coverage cirrus deck to around 10 kft by midnight, further 
lowering to around 5 kft after daybreak on Sunday. Modest confidence 
we will see intermittent light rain break out over our inland sites 
by around noon on Sunday.

Extended Outlook...A storm system will bring periods of MVFR/IFR 
late Sunday through Tuesday. Otherwise, expect VFR.


As of 1230 AM Saturday...Winds are diminishing on schedule and 
no significant changes are needed to the forecast. Discussion 
from 900 AM follows...

High pressure building in from the upper Midwest is keeping a 
rather tight pressure gradient over the Carolina coastal waters,
with recently observed wind gusts as high as 25 knots at the 
Frying Pan Shoals buoy, 17 knots at Wrightsville Beach, and 17 
knots at the nearshore Sunset Beach buoy. These stronger winds 
should maintain themselves for the next several hours before 
diminishing this afternoon. An exercise caution headline will 
remain on the forecast north of Cape Fear through 1 PM.

As of 300 AM Saturday...The center of high pressure to out N on 
Sunday will shift offshore Sunday night. A warm front and coastal 
front will develop Sunday night and then remain in close proximity 
Monday and Monday night. Return flow around the departing high will 
allow winds to veer from NE Sunday to E and SE Sunday night. The 
juxtaposition of the front will ultimately determine the wind 
direction for the remainder of the period. At this time, we think 
winds will tend to veer to S and SW across the waters late Sunday 
night into Monday as high pressure moves offshore. Developing low 
pressure along the front would tend to shift winds back to the NE 
during Monday with winds perhaps returning to E and SE overnight 
Monday depending on the evolution of the the coastal front. Wind 
speeds will be in the range of 10 to 20 kt through the period. Seas 
of 2 to 3 ft Sunday and Sunday night will build to 3 to 4 ft Monday 
and Monday night.

As of 300 AM Saturday...Low pressure moving along the coast will 
create SCA conditions on Tuesday. Uncertainty remains into the 
strength and position of this system, but if the low stays along the 
coast or just inland as currently projected, S/SW winds of 15-25 kts 
will envelop the waters Tuesday, driving seas to 4-7 ft, and an SCA 
is likely. As the low pulls away Tuesday night, a trailing cold 
front will cross the waters turning winds to the NW, with wind 
speeds then slowly falling to around 10 kts by the end of the 
period. These lighter winds combined with the offshore direction 
will allow seas to fall to 2-3 ft during Wednesday.






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