Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 221633
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1133 AM EST Sun Jan 22 2017

.SYNOPSIS...
A complex and potent storm system will affect the Carolinas
today through Monday with potential for severe weather late
this afternoon and evening. Total rainfall amounts through
Monday should amount to one to 2 inches. This storm system will
slowly depart through Monday leaving high pressure for Tuesday
and Wednesday. The next cold front will move across the area on
Thursday. Much colder weather will follow Friday and into next
weekend. In the meantime a lull in PCPN mainly isolated to
scattered then categorical rain starting 5-6 PM moving in from
the SSW. The previous forecaster discussion follows.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1134 AM Sunday...Primary severe threat will be this
evening and essentially we see this line moving through southern
Alabama approaching the Florida panhandle presently. A squall
line should be ongoing...traversing NE SC and SE NC between 7PM
over the interior of NE SC to around midnight exiting the coast
north of Cape Fear. Primary hazards are damaging winds and a
tornado potential. In the meantime a lull in PCPN mainly
isolated to scattered coverage then categorical rain starting
5-6 PM moving in from the SSW. The previous forecaster
discussion follows.

Two more rounds of pcpn will affect the ILM CWA during the next
24 hrs. The 1st is currently now overhead with mainly
stratiform rains with embedded heavier showers. The pcpn from
Sat evening helped to stabilize the airmass across the FA prior
to this next pcpn area. The embedded thunderstorm activity over
GA and southern SC will fall apart by the time it reaches the
ILM CWA during this morning. QPF from this pcpn round will run
around one quarter of an inch for the ILM NC CWA up to one half
inch or slightly hier for the ILM SC CWA. Will see a brief
reprieve from the pcpn from midday thru mid-afternoon.

The next round of pcpn, and potentially the more potent, will
occur from late this afternoon through late this evening. The
pcpn will overspread the FA from SW to NE. A closed upper closed
low will move from the Gulf Coast States this morning, to the
western Carolinas this aftn thru tonight. It`s accompanying sfc
low will quickly get captured by this upper closed low later
today...and become a somewhat vertically stacked system by Mon
daybreak. Plenty of dynamics aloft and at the sfc will be in
play with this next round of pcpn. As for severe convection
potential, the FA will experience a High Wind Shear environment
and a Low Cape, instability environment. Do not need much
instability when you are dealing with plenty of atmospheric
dynamics, especially this much low level wind shear. Thus, with
plenty of twisting in the low levels, rotating tornadic type
thunderstorm activity is possible beginning late this aftn thru
this evening. Will advertise the possible tornadic threat with
damaging wind gusts and hail.

The low`s occlusion portion of it`s frontal system, will push
across the FA from west to east during the mid to late
evening hours. After pushing thru, the pcpn will come to an
abrupt end. A dry mid-level punch is the mechanism for pushing
this occluded front across the ILM CWA and likely where you will
find the most intense pcpn prior to it pushing thru. Will
indicate isolated showers after it`s passage for the remainder
of the overnight.

Temperatures will run up to 15 degrees above normal this period.
The CAA after the pcpn comes to an end will lag-some, with the
best of it occurring during the next period. As a result, do
not expect your normal diurnal temperature curve this period.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
As of 430 AM Sunday...The Fa will be under the mid-level dry
air associated with the "dry punch" that pushed across Sunday
night. During Monday, expect the wraparound moisture to push
across the FA associated with the Closed Upper Low moving from
the western Carolina to only off the DELMARVA Coast by Tue
daybreak. Dynamics from weak mid-level vorts rotating around the
slowly lifting upper closed low will result in low topped
isolated to scattered showers across the FA, especially during
the daytime heating on Mon. This pcpn threat will diminish
quickly after nightfall Monday. However, low level clouds will
continue to persist thru Monday night. For Tuesday, the WNW-NW
downslope wind directions thru the atm column will scour out any
remaining moisture resulting in finally a Sunny sky for Tuesday
and a Clear Tue night. Temps thru the period will slightly
lower from each previous max and min temp occurrences. The
exception may be for Tue highs when a downslope trajectory may
add several degrees to Tueday`s highs. The CAA will end Tue
morning with various thickness schemes rising indicative of WAA
especially aloft. Overall, followed a consensus amongst the avbl
model Mos Guidance except for Tue highs where several degrees
were added due to ongoing WAA and the downslope trajectory thru
the atm column.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 3 AM Sunday...Period begins warm and dry with surface
high off the east coast and mid level ridge axis overhead.
Ridging aloft shifts off the coast during Wed but subsidence
will continue suppressing upward motion while pushing highs
close to 70 degrees. Cold front moves across the area Thu
morning possibly accompanied by isolated showers, however low
level convergence is weak and the front lacks strong dynamical
support. Inherited low chc pop may be a little generous but will
not make any changes at this time. Regardless of shower
coverage any rainfall would be meager if forecast soundings are
correct in showing a brief 6 hour period of precipitable water
values over 1 inch. By Thu afternoon PWATs are around 0.30 inch.

Following the cold front cooler air will start building into the
region, but its arrival is likely to be later Thu which will result
in one last day with temperatures above climo. 850 temps drop 5-10
degrees C between Thu morning and Fri morning and highs on Fri may
struggle to reach climo (mid 50s). Temperatures will trend even
cooler for the weekend with a reinforcing shot of cold air Sat
keeping highs around 50 with lows hover around freezing. Deep
westerly flow will keep skies mostly clear and prevent any
rainfall.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
As of 12Z...VFR cigs have been occurring at the coastal
terminals, while MVFR cigs are most prominent just inland. Winds are
westerly, with light-moderate mostly stratiform rain moving NE
across the southern terminals.

Model guidance is bullish on re-developing IFR cigs this morning as
a warm front lifts northward. This appears likely as the frontal
inversion lowers. Stratiform rain will also become more widespread
and increase in rate, further saturating the low levels. After the
warm front moves through in the late morning/early afternoon, should
see precipitation end, winds veer to the SW, with flight category
improvements to MVFR, then VFR. The exception may be KLBT which may
remain MVFR through the afternoon. The final round of precipitation,
with an increased potential for MVFR/IFR and possibly severe
thunderstorms, will occur 21Z-05Z. This will be associated with an
intensifying upper closed low and its accompanying sfc low. Gusts up
to 45 kt are possible during the convection this evening.

Extended outlook...Expect mainly VFR, except for possible
MVFR/IFR during Mon from clouds and reduced vsby from pcpn.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1134 AM Sunday...SCA all waters thru Tue afternoon.

Looking at SSW to SW winds increasing to the 15 to 25 with
gusts to 30 kt this aftn and evening. Some guidance indicates
winds may temporarily back to the SSE-SE prior to the pcpn
ending. For now, will hold onto the SSW-SW directions. The
cooler shelf waters will help prevent the higher winds just off
the deck from reaching the sfc. The possible convection moving
across the area waters will have the capability to tap those
stronger winds aloft and bring them down to the ocean sfc. This
will be advertised in the Hazardous Weather Outlook.

Significant seas will build to 5 to 8 ft by late this aftn and
persist in the 6 to 9 foot range tonight...highest off Cape
Fear. Wind driven waves at 4 to 7 second periods will dominate
the significant seas. An underlying 10 second period 1 to 2 foot
easterly ground swell will remain present.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 400 AM Sunday...SCA will be ongoing at the start of this
period and will extend thru 6 pm Tuesday.

Cyclonic flow aloft and at the sfc will dominate the local
waters thru Tuesday. This due to a closed low and it`s
accompanying sfc low, now stacked" moving from the Western
Carolinas to off the DELMARVA Coast Tue morning, and to off
Cape Cod by Wed morning. Sfc ridging from Florida will extend
northward across the local waters Tue night. A tightened sfc pg
will be ongoing at the start of this period and will very, very
slowly relax with time. Looking at SCA speeds Mon into Tue, with
SCEC speeds late Tue and Tue night. Directions will run SW
becoming WSW late Monday...and W to WNW during the day on
Tuesday. Decent CAA Mon into early Tue will help keep the winds
elevated. Significant seas thru Monday Night will run 4 to 7
ft, except up to 8 ft south of Cape Fear to Little River Inlet
during day Mon night due to the fetch associated with the
westerly wind direction. Seas will finally subside late Tue aftn
thru Tue night to a 2 to 4 foot range, except remaining
somewhat elevated across the waters south of cape fear to Little
River Inlet due to the fetch associated with westerly wind
direction.

LONG TERM /WEDNESDAY THROUGH THURSDAY/...
As of 3 AM Sunday...Southwest flow around western side of high
pressure will gradually increase Wed and Wed night as gradient
increases ahead of a cold front. Front moves across the waters
late Thu morning with offshore flow developing in the afternoon.
Ahead of the front southwest winds will peak around 20 kt Wed
night and Thu morning. Winds veer to west-northwest Thu
afternoon with speeds remaining 15 to 20 kt into Fri morning.
Seas 2 to 3 ft at the start of the period will build to 3 to 5
ft later Wed and could exceed 6 ft in some areas late Wed night.
Cannot rule out short duration SCA just prior to the front
passing. Post front offshore flow will knock seas down, from 3
to 5 ft Thu afternoon to 1 to 3 ft Fri morning.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory until 6 PM EST Tuesday for AMZ250-252-254-
     256.

&&

$$

NEAR TERM...DCH/8
SHORT TERM...DCH
LONG TERM...III
AVIATION...DCH


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