Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 290245
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1045 PM EDT Tue Mar 28 2017

.SYNOPSIS...
a cold front which will drop south across the area by late
tonight or early Wed. Relatively cooler and drier high pressure
will build in from the north Wed into Thu night. Showers and
thunderstorms are expected on Fri as warmer and more humid air
returns ahead of an approaching cold front. The cold front will
sweep eastward across the area and offshore late Fri night.
Some of the thunderstorms may become strong to severe Fri. The
weekend should be dry and warm on Sat with temps dropping back
to near normal on Sun as high pressure builds in from the Great
Lakes.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 945 PM Tuesday...Sfc cold front will sink slowly across
the area overnight. The convergence along this front is evident
with Cu and SC strewn along it from west to east. A few of these
Cu are building just enough to produce isolated showers.
However, aloft, NVA ie. Subsidence, is now affecting the FA with
the mid-level s/w trof having pushed off the DELMARVA Coast
this evening. As a result, do not expect much vertical
development with these showers. May continue the slight chance
POP well into this evening as this boundary drops southward.
Not much tweaking to tonights lows from the previous fcst
update. However, am concerned for the possibility of fog
eventhough models are not highlighting its potential. Will
update to include patchy for now and could get worse with time
depending how much drier air, ie. lower dewpoints, are able to
advect into the FA overnight. Seen it many times after FROPA in
the evening and winds go NW to N less than 5 kt. And with ground
moisture avbl from rainfall having occurred earlier today and
also late this aftn and evening.

Previous.....................................................
As of 3 PM Tuesday...A second shortwave is crossing the
Carolinas this afternoon and with the early shortwave there has
been a delay in additional convection developing. The GOES-16
1-minute imagery is showing cumulus developing west of Florence
to Pembroke and isolated cumulus developing to the west. The 16
UTC HRRR is only showing isolated convection through sunset. So
will keep a 20 to 30% chance of convection with the higher
chances for the northern coastal areas.

The frontal boundary will shift across the area after midnight and
sweep to the south with high pressure building in the area into
Wednesday. Lows tonight are expected to fall into the upper 50s and
highs on Wednesday to around 80 except cooler at the beaches with a
northeast flow.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 3 PM Tuesday...Mid level ridge axis over the southeast will be
deamplifying and shifting east Wed night as surface high over
southern Canada builds down the east coast. Cooler air associated
with the Canadian high spreads over the region Wed night with lows
dropping close to climo. Northeast winds will be in the 5 to 8 mph
range which should prevent any radiational cooling. Low will be in
the low to mid 50s across much of the area. Surface high shifts off
the coast later Thu with weak return flow developing Thu night.
Ridging aloft Wed night and Thu will keep the region dry through at
least Thu evening. Forecast soundings show impressive subsidence
from 850mb through 700mb into Thu night before approaching high
amplitude southern stream system shunts the 5h ridge axis
farther off the coast.

Developing deep southwest flow Thu night increases moisture in
the region, precipitable water values increase from around 0.80"
Thu evening to 1.40" by the end of the period. Arrival of this
deeper moisture along with an increase in mid level lapse rates
should open the door for some convection late in the period. The
unfavorable timing and lack of strong low level jetting does
suggest coverage will be rather limited and do not plan on much
in the way of changes to inherited Thu night precip chances.
Temperatures Thu will be near to slightly below climo, upper 60s
to lower 70s, with temps Thu night running above to well above
climo and likely following an atypical curve with slight warming
after midnight.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 300 AM Tuesday...Next in series of potent southern stream
systems will impact the eastern Carolinas Fri and Fri night with
a categorical risk for showers and thunderstorms developing.
The combination of significant upper level support and strong
and deep moisture return and lift provides at least the
opportunity for a more widespread and significant rainfall
event. There will be some risk for strong to severe
thunderstorms during this time. 0-6 km effective bulk shear
parameters are not particularly impressive. However, instability
does grow with mixed layer CAPE values on the order of 500 to
1000 J/kg as the warm front should move to our N. Mid-level
lapse rates are forecast to be rather modest. The potential is
there for an active day/night leading into the weekend, although
magnitude is certainly still a question mark.

In the wake of this system, dry weather and near to above
normal temps are expected for the weekend as mid-level ridging
builds across the area and surface high pressure builds from the
NW and N. Attention then will turn westward as next southern
stream system along the Gulf Coast Sun night lifts to the NE and
drags a warm front to the N. This will again bring deep
moisture into the Carolinas, and with that, showers and
thunderstorms early next week. Given timing differences between
long range models and a general slower trend as compared to 24
hours ago, will cap POPs in the chance category until we can
gain better resolution as to when the highest risk for showers
and thunderstorms will occur.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
As of 0230Z...Updated the pre-dawn Wed hours for all 5 terminals
to include 3sm to 4sm in BR. Upstream, a few sites across
Eastern NC have seen their vsby drop due to fog. In fact, the 2
sites exhibiting fog, KISO and KGWW, have dropped to 1/2 mile
in FG. Will refrain from including FG at this update but will
monitor.

Previous.................................................
As of 00Z...Sfc convergent boundary lies along an east to west
line extending from Surf City across Whiteville to Hartsville.
This feature is a product of storm outflows and the sfc cold
front sinking southward. Isolated low topped showers and
possibly a thunderstorm will likely continue to develop along
this boundary as it sinks southward for the next few hours. With
subsidence aloft, do not expect much vertical development. Will
only carry VCSH for the associated terminals near this boundary.
The remainder of the night will see improving ceilings and
winds that slowly veer from SW-W to NW-N overnight...and to the
NE during Wed. Wind speeds mainly 5 to 10 kt early this evening,
dropping to 2 to 4 kt overnight after the CFP. None of the near
term guidance is illustrating fog development for the pre-dawn
Wed hrs. May place patchy MVFR fog at press time or amend later
on this evening if 00Z Model guidance shows it. No ceilings or
pcpn for daylight Wed. Only concern will be the slow veering
wind direction trend from NNW-NNE at sunrise to ENE to E at
sunset. Wind speeds thruout the day at 5 to 10 kt. The coastal
terminals may see an aftn/early evening seabreeze develop with
winds from the SE around 10 kt.

Extended outlook...VFR conditions Thu. MVFR/IFR conditions
likely in showers and strong to severe thunderstorms Fri/Fri
night. VFR conditions Sat thru Sun.

&&

.MARINE...
NEAR TERM /THROUGH WEDNESDAY/...
As of 945 PM Tuesday...Update concerned with pcpn eventually
ending late this evening. And, re-adjusting the winds based on
the slowly southward dropping sfc boundary that will result in
winds becoming NW to N after its passage during this evening
thru the pre-dawn Wed hours. The sfc pg is rather loose on
either side of the sfc cold front, resulting with only 10 to 15
kt wind speeds being fcst. Significant seas will run 2 to 4 ft
with 5 footers across the outer waters off Cape Romain and Cape
Fear. The healthy SE ground swell at 10 to 11 second periods
has peaked during today and should now exhibit a slow decaying
trend. Will see wind driven waves become more dominant in the
seas spectrum later Wed as NE winds increase due to sfc ridging
down the east coast from Canada becoming more prominent.

Previous....................................................
As of 3 PM Tuesday...SW winds around 15 knots with higher gust
are seen at coastal CMAN stations...not receiving any offshore
buoy data at this minute so have lower confidence of the current
wind speeds at 10 to 20 miles off the coast. With cold front
approaching expect to see winds increase to 15 to 20 knots with
higher gust. Seas are expected to peak at 3 to 5 feet. Will
continue to see longer period swells through this evening. With
the cold frontal passage expected between 2 AM and 6 AM
Wednesday, seas will slowly fall to the 3 to 4 feet range by the
end of Wednesday.

SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 3 PM Tuesday...Northeast flow will continue Wed night and
Thu as high pressure over southern Canada builds south.
Gradient becomes pinched late Wed night as cold surge moves
across the waters and northeast flow may briefly hit 20 kt.
Northeast flow remains 15 to 20 kt Thu before starting to
decrease and veer to east Thu evening and then southeast Thu
night as the surface ridge axis moves offshore. Seas will range
from 3 to 5 ft through Thu night with shorter wave periods
expected given the strength of the northeast flow. Exercise
caution headlines may be needed during the period, depending on
the strength of the northeast surge late Wed night.

LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 300 AM Tuesday...A Small Craft Advisory is likely for all
waters Fri and Fri night with conditions possibly lingering
into Sat.

Slow moving area of low pressure will be moving across the Ohio
Valley Fri. Its accompanying warm front will move across the
waters Fri. As low pressure moves offshore of the Mid-Atlantic
states late Fri night and Sat morning, it will strengthen and
drag a cold front across the waters. High pressure will slowly
build across the area from the N and NW Sat night and Sun.

SE winds Fri morning will become S and then SW Fri night. The
wind direction will become westerly early Sat morning and then
NW by Sat afternoon. N winds Sat night will become NE overnight
Sat with NE winds persisting into Sun before veering to easterly
during the afternoon.

The strongest winds are expected Fri and Fri night, up to 20 to
25 kt. Seas late Fri and Fri night will build to 4 to 7 ft and
around 8 ft at frying Pan Shoals. Seas during Sat will only slowly
subside as backswell from departing storm system impacts the
waters. Seas should drop below advisory levels by late Sat and
to 2 to 4 ft on Sun.

&&

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

&&

$$
SYNOPSIS...DCH
NEAR TERM...DCH/DRH
SHORT TERM...III
LONG TERM...RJD
AVIATION...DCH



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