National Weather Service United States Department of Commerce

 


000
FXUS62 KILM 250224
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1024 PM EDT Sat Sep 24 2016

.SYNOPSIS...
A backdoor cold front will come through early Sunday but it may
stall close enough to keep the weather unsettled into early next
week. A stronger cold front arrives Tuesday night into Wednesday
with some drying and cooling beginning Thursday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of 1030 PM Saturday...No changes to the forecast with the
latest update. Previous discussion follows:

Tropical moisture surrounding a very persistent low pressure area
finally moved south of the area last night, allowing drier weather
to build in from the north. We`ve got shallow cumulus near the
coast south of Cape Fear due to residual low-level moisture,
however a subsidence inversion around 5500 feet AGL is keeping the
lid of these clouds. Convective inhibition (CIN) as large as 60
J/kg is expected to be unbreakable by the weak seabreeze, leaving
us with a dry forecast this evening into tonight.

A cold front moving quickly southward through Virginia should reach
the eastern Carolinas between 5-10 AM Sunday. Although the front is
now currently outlined by fairly dense low clouds, increasingly dry
air in the 925-850 mb layer should erode a good deal of these clouds
as the boundary moves south. Light winds and clear skies ahead of
the front should allow patchy fog to develop late tonight.
Lows mainly upper 60s with some lower 70s on the beaches.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
As of 300 PM Saturday...High pressure dropping southeastward across
the eastern Great Lakes will push the cold front through the area
Sunday morning. Behind this front, northeasterly winds will push
heavily modified Canadian air into the eastern Carolinas. This air
will have spent the past 400-500 miles traversing the very warm
western Atlantic Ocean and will have picked up a good deal of
moisture. Throw in some sunshine and steep low-level lapse rates and
scattered showers and t-storms should develop Sunday afternoon.
Forecast PoPs are as high as 40 percent centered on the Burgaw-
Whiteville-Marion corridor where it appears a mesoscale area of low-
level convergence may develop due to the proximity of the front and
the shape of the coastline from Cape Lookout to Myrtle Beach.

As the high moves across New England Sunday night and into the
Atlantic Monday afternoon, our northeasterly low-level flow will
gradually turn easterly, perhaps even southeasterly Monday night.
These onshore winds will advect in enough moisture to support 20-30
percent chances of showers, most numerous across South Carolina.
Ridging aloft should keep these showers from becoming too numerous,
however it`s interesting to note that both the 12z ECMWF and 12z GFS
bring a mid-level wave across the area Monday night that could
enhance the potential of showers. I`ve bumped PoPs up a bit for that
potential.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 300 PM Saturday...Showers and isolated thunderstorms are
looking more and more likely on Tuesday. Cold front will be
heading our way and accompanied by decent height falls aloft. The
main factor arguing against precip being the position of the upper
low leading to westerly flow aloft locally. Despite this models in
pretty good agreement with some coverage of storms. Energy diving
into the western part of the mid level trough will slow the
surface boundary and there may even be a wave that develops just
off the coast for a continuation of rain chances into Wednesday
especially along the coast. Then strong dry advection and
moderately strong cool advection Wednesday night into Thursday. A
cooler early Fall airmass expected to round out the long term.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
As of 00Z...Anticipate fog development overnight into the
early morning hours, with patchy areas of low cigs inland as well.
After daybreak, expect conditions to improve to VFR with afternoon
isolated SHRA/TSRA possible along and behind a backdoor cold
front.

VFR prevails this evening at all terminals with light winds and
nearly clear skies. With increased low level moisture, light
winds and radiational cooling, anticipate fog development to
create MVFR/IFR overnight into the early morning hours on Sunday.
Would not entirely rule out areas of low cigs inland as well.
After daybreak, conditions improve to VFR with northeasterly winds
around 5 kts becoming east-northeasterly in the afternoon to near
10 kts. Along and behind the backdoor front, isolated showers and
thunderstorms are possible in the afternoon and evening hours.

EXTENDED OUTLOOK...Chance for SHRA/TSRA Tue through Wed.
Otherwise expect VFR.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1030 PM Saturday...No changes to the forecast with the
latest update. Previous discussion follows:

A cold front currently moving south through Virginia should reach
the Cape Fear to Cape Romain area between 5-10 AM Sunday morning.
Out ahead of the front we expect northeast winds 10 knot or less
to continue. The front will come through dry but should result in
increasing northeasterly winds, most noticeable during the day
Sunday.

Area buoys are reporting anywhere from 1 foot seas just off Sunset
Beach to 3 foot seas near and east of Cape Fear. Seas consist of a
mix of 10-second easterly swell from Tropical Storm Karl out near
Bermuda, and local wind waves averaging 4-second period. Karl`s
swell may build by another 0.5 to 1.0 foot by late tonight, mainly
realized in the waters north & east of Frying Pan Shoals.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 300 PM Saturday...High pressure moving eastward across the
Great Lakes and into New England Sunday will drop a cold front
across the area Sunday morning. Behind this front, northeasterly
winds will strengthen to a solid 15 knots with some gusts near 20
knots expected Sunday afternoon into Sunday night. The high will
move off of the New England coast Monday afternoon, allowing our
winds to gradually turn easterly, then southeasterly Monday night.

Karl`s 10-second easterly swell will remain with us through Sunday.
When combined with a shorter period wind chop, combined seas of 3-4
ft are expected Sunday, diminishing to 2-3 feet Monday.

LONG TERM/TUESDAY THROUGH THURSDAY/...
As of 300 PM Saturday...Prefrontal southerly winds develop on
Tuesday after possibly starting the day light southeasterly. Not
much of a wind increase as the day wears on due to the approaching
front now a bit slower. Its passage late Tuesday night may be
followed by its stalling just off the coast so the wind and seas
forecast is a bit muddled beyond Tuesday night. The 00z ECWMF
didn`t even have FROPA until Wednesday night. Despite the
uncertainties there still seems to be no big cool push (that might
necessitate some headlines) during the period-but there may be
just beyond.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.

&&

$$

SYNOPSIS...MBB
NEAR TERM...REK/TRA
SHORT TERM...TRA
LONG TERM...MBB
AVIATION...SGL
MARINE...REK/TRA/MBB