Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 201117
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
717 AM EDT Sat May 20 2017

.SYNOPSIS...
Bermuda high pressure offshore will extend inland, helping to
maintain fair and very warm conditions. Thunderstorms will
begin to increase early next week ahead of a cold front from the
west with unsettled conditions persisting for much of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 545 AM Saturday...Have updated the sky coverage and
increased the fog across the FA for this morning.

Areas of fog and low clouds, with pockets of dense fog, have
engulfed the forecast area early this morning. This seen clearly
with sat imagery trends, specifically the 11-3.9 micron IR
imagery. The low stratus clouds will actually help prevent the
pockets of dense fog from increasing in areal coverage. Thus, a
dense fog advisory is not required at this point. Look for the
mid to late May sun quickly burnoff and dissipate the fog and
low clouds by mid morning.

Previous Thinking.........................................
As of 315 AM Saturday...A narrow mid level ridge will build
just west of the forecast area today. This will push a weak
boundary from the north to basically bisect the area by early
Sunday morning. This boundary may provide just enough impetus to
kick off a few showers and thunderstorms across the northern
zones late this afternoon and early evening before the loss of
daytime heating. We continue to advertise slight to lower chance
pops to address this possibility. Afternoon highs are expected
to be 3-5 degrees warmer vs. Friday`s values as the close
proximity of the ridge warms thermal profiles. Lows for Sunday
morning should be in the middle 60s once again as there is
little cool air in the wake of the front at least initially.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 315 AM Saturday...This will be a transition period with regard
to the longwave pattern aloft. The upper ridging and associated
fantastic wx experienced across the FA for much of the past week,
will get booted east of the FA by late this period as successive s/w
trofs aloft carve out a large amplitude upper trof. Initially, this
upper trof will lie across the Central U.S. but then is progged to
expand to the East Coast of the U.S. by the end of this period. The
upper trof axis will remain positively tilted and generally
extending from the Great Lakes to Texas. This position will result
in Gulf of Mexico moisture being tapped with low level Atlantic
moisture also available.

At the start of this period, a stalled frontal boundary will roughly
lie across the NC-SC border. Could see widely scattered convection
along this boundary due to weak forcing. The atm aloft will start
out quite dry early Sun with increasing moisture to occur with PWs
increasing to 1.50 to 2.00 inch range  Sun night and continuing thru
Mon night. The sfc frontal boundary will lift north of the FA by Mon
followed by the approach of a cold front from the west during Mon.
This front is progged to stall, oriented NE to SW, across the the
eastern Carolinas. Forcing ahead of this front along with weak mid-
level s/w trofs migrating across the FA, spells an extended period
of convection and thus POPs have been adjusted hier to likely to
categorical by late Sun night thru Mon night. At the moment, WPC
pcpn amounts during this period remain modest at best but will need
to monitor future model runs with regard to any increase to pcpn
amounts across the FA.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 3 PM Friday...Pattern turns rather unsettled for most of the
period, though a few timing and placement issues of the frontal
boundary may still need some resolution in future forecasts. A brief
respite is possible early Tuesday as deep upper troughiness
amplifies over the Great Lakes. This will keep the front active
along with its associated moisture, possibly bolstered with Gulf
moisture. The speed with which this occurs is not well agreed upon
between various models. This moisture may encroach as early as
Tuesday but Wednesday is appearing more likely. The upper trough and
surface cold front drive through decidedly later Wednesday and wind
fields may be strong enough to support a small severe weather
threat. Cool and dry air advection appear slated for Thursday and
Friday.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...

As of 12Z Saturday...LIFR/IFR conditions across all terminals
this morning thru 14Z. There-after, expect mainly VFR
conditions through midnight tonight followed by possible
MVFR/IFR conditions toward daybreak Sun due to the frontal
boundary dropping southward and in close proximity.

From 12Z to 14Z, the area terminals will experience low
ceilings and/or vertical vsby below 1k ft along with
horizontal vsby from 1/4 to 1sm in FG and BR respectively.
The mid to late May insolation should burnoff and dissipate
the fog and low clouds rather quickly.

The backdoor cold front will drop southward to the area late
today before stalling along the NC-SC border tonight. Ahead of
the front, the local terminals will observe another summer`s
day with temps in the 80s to around 90 inland. Expect cu
development, however it`s vertical development will be retarded
due to the subsidence inversion between the 900mb-850mb levels.
Thus no convection is expected ahead of this front.

Extended Outlook...Reduced flight categories will be possible
in widely scattered showers and thunderstorms during
Sunday...becoming more numerous late Sunday night thru
Wednesday.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 315 AM Saturday...A weak southwest flow is currently in place
across the waters this morning and this should persist most of the
near term period. Speeds are hovering a little less than ten knots
and may increase a little with the development of the sea breeze
later. The direction may back a little to the south as well. Late
tonight a back door front sneaks down and the northern zones will
see winds acquire a northerly component. Significant seas will
remain limited with the light forcing on the order of around two
feet.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 315 AM Saturday...The beginning of this period shows a stalled
front extending inland along the NC-SC border. The placement of
this front will have a bearing on wind directions across the
local waters. Wind speeds initially will be around 10 kt due to
a weak sfc pg. The stalled front will lift north of the local
waters Monday followed by the approach of the next cold front
from the west that models stall across the Eastern Carolinas by
the end of this period. Look for winds to become S to SW thruout
late Sun night thru Mon night with speeds increasing to around
15 kt. Significant seas thru Sun night will hover around 2 ft.
For Mon thru Mon night, seas will build to 2 to 4 ft due to the
increasing short period wind driven waves. Not much of any long
period swell expected this period, just the 3 to 6 second short
period seas.

LONG TERM /TUESDAY THROUGH WEDNESDAY/...
As of 3 PM Friday...Placement of the frontal boundary will
be crucial to wind directions WITH WIND SPEEDS AT OR BELOW 15
KT EITHER SIDE OF THE FRONT. Flow turns back to the SW by
Wednesday with the approach of the next cold front. This second
boundary will be stronger at the surface and also accompanied by
stronger wind fields aloft. Conditions may worsen to Advisory
levels.

&&

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

&&

$$
SYNOPSIS...SHK
NEAR TERM...DCH/SHK
SHORT TERM...DCH
LONG TERM...MBB
AVIATION...DCH


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