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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KILM 221012
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
612 AM EDT Sun Apr 22 2018

.SYNOPSIS...
-- Changed Discussion --
Canadian high pressure will continue to extend into the
Carolinas today as it migrates slowly east off the Mid-Atlantic
coast. A slow moving low pressure system will cross the
Southeastern U.S. and produce beneficial rains of 2 to 4 inches
over a 2 day period from Monday thru Tuesday. Temperatures below
normal thru Tuesday will bounce back to near normal for the rest
of the work week with the threat for additional rainfall Thu
into Fri from the next low pressure system.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 3 AM Sunday...Surface high just north of the Outer Banks this
morning will gradually retreat northeast today into tonight as
stacked low slowly drifts from the southern plains states into the
Lower Mississippi Valley. Deep dry air remains over the region into
tonight with precipitable water not climbing over half an inch until
mid afternoon to early evening. Low level onshore flow gradually
helps increase boundary layer moisture, but flow aloft remains west-
northwest until very late in the period. This prevents any
meaningful moisture return until late tonight, when the mid-level
pattern starts to change and deep southwest flow develops. Most
areas do not see precipitable water exceed one inch until very late
in the period. Expect another dry day today with temperatures
running a little below climo. High cloud spreads over the area from
the southwest during the day, gradually thickening throughout the
day. Increasing cloud cover will limit afternoon heating a bit,
especially across inland SC. However, temperatures starting out
several degrees warmer than yesterday will lead to highs ranging
from the upper 60s along the coast to low to mid 70s inland.

As the stacked low moves into the Lower Mississippi Valley tonight
it helps pull a weak coastal trough onshore. This aids low level
moisture return and leads to increasing/lowering cloud cover.
Increased east-southeast winds will also help keep temperatures
warmer with lows likely to end up a few degrees above climo, mid 50s
for most areas. Latest guidance shows 850/700 mb frontogenesis and
increasing divergence aloft moving into the forecast area as the
period ends. These features are also near the Theta E ridge,
something which suggests heavy rain will be poised to move into the
forecast area very late or just after the end of the period. Given
guidance does tend to start precip a bit early have slowed down
arrival of precip late in the period.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
As of 400 AM Sunday...The time frame extending from the start
of this period, 6am Mon, thru Tuesday daylight morning, the
local FA will see nearly a continuous shield of light to
moderate stratiform type rains. Embedded in this shield of
rainfall, will be a few thunderstorms. For the most part, the
tstorm activity will occur over the Atlantic waters and given
the trajectory of the swath of pcpn moving onshore, the coastal
counties will be the 1st in line to experience a few of these
storms. As the pcpn moves further inland, the lack of
instability will keep tstorms from further developing or in this
case, from progressing too far inland before it`s demise.

Models indicate an expansive area of strong UVVs across the FA
and surroundings for a good 24 to 36 hrs. This a result of
synoptic difluence aloft due to the positioning of the upper
closed low as it moves from the lower Mississippi Valley Monday
morning, to eastern Tennessee late Tue night before finally
opening up to a s/w trof by Wed. Model soundings indicate 50+
kt East to Southeast winds pumping in low level Atlantic
moisture across the Carolinas. Gulf of Mexico moisture will have
already been and continue to be tapped but by this time the main
source will be Atlantic moisture.

Forecast rainfall amounts during this 2 day period will range
from 2 to 4 inches. Isolated higher amounts are possible mainly
along the immediate coast due to the onshore movement of any
convection before dying out as it pushes further inland into a
more stable atm in the low levels. This modest rainfall amounts
over a 2 day period will be extremely beneficial to farmers and
local growers. Crops, plants, trees and etc, will literally act
like sponges and absorb this water. And given the 2 day period
of these rains, we do not expect high runoff problems.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 300 PM Saturday...A low pressure system will track off to
the NE Tues into Wed. The sfc low will track closer to the
coastline while the upper low will move northeast from TN toward
the Ohio Valley. As this closed upper low lifts north, another
shortwave will rotate down toward the Southern Appalachians by
Thurs. Overall, this system remains quite complex, but looks
like the heavier rain will move north leaving clouds but some
drier air wrapping through mid week. The next shortwave should
dig down and push a cold front through on Thurs, but does not
look like a big rainmaker. Therefore, expect breaks in the
clouds and some clearing late Tues into Wed with increased
clouds and potential for pcp again Thurs. Another system will
follow in this progressive flow by Fri into Sat, although the
GFS keeps most of the weather with this system north of our
local forecast area, while the ECMWF remains more pessimistic
heading into next weekend. Overall a good amount of clouds and
and not much QPF expected through the week. Temps have been
trending warmer but remaining near normals through much of the
period.

&&

.AVIATION /10Z SUNDAY THROUGH THURSDAY/...
As of 06Z...Although low level moisture is slowly increasing, do
not expect much in the way of fog this morning. Boundary layer
moisture remains on the low side for fog and there appears to be
just enough in the way of boundary layer mixing to prevent
anything more than fleeting patches of fog. Will carry VFR
through the valid TAF period. East winds will be light through
the overnight before increasing to 10 to 15 kt later this
morning and for the afternoon. Clouds gradually increase today,
with ceilings starting to lower from southwest to northeast
this evening.

Extended outlook...Rain Monday and Tuesday could bring periods of
MVFR/IFR conditions in low ceilings and visibility. The worst
conditions are expected Monday night. Wed/Thu VFR.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 3 AM Sunday...Easterly winds will steadily increase
through the period, becoming more southeast late tonight.
Surface high north of the Outer Banks this morning will
gradually retreat northeast today as low pressure moves east
toward the southeastern states. Gradient will slowly become more
defined and winds will increase from 10 to 15 kt later today to
15 to 20 kt this evening and overnight. Increase in wind speeds
combined with onshore flow helps build seas from 2 to 3 ft this
morning to 3 to 5 ft by evening. Seas continue building tonight
and it is likely seas will reach 6 ft a few hours prior to the
end of the period. Thus the previously raised Small Craft
Advisory will remain in effect.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 400 AM Sunday...SCA conditions will start off this short
term period as a well tightened sfc pg settles across the local
waters. This sfc pg will tighten some more by mid-afternoon Mon
and continue thru Tuesday morning except late morning for the
waters north of Cape Fear. Various model soundings indicate 50+
kt sustained winds at only 450 ft to 800 ft above the ocean
sfc. With East to Southeast winds pushing offshore Gulf Stream
waters toward the coast. With 70+ degree SSTS already lurking
just offshore, ie. 41013 at 70.0 degrees F, the thinking is
enough of this warm water will be in play for those strong winds
just off the deck to mix down to the ocean sfc. Thus a Gale
Watch has been issued for all waters from Mon afternoon thru
late Tuesday morning. Have left a 3 hr buffer on the ending of
the Gale Watch due to closed Lows will at times not follow the
latest model fcsts. Significant seas will build rather quickly
and primarily will be wind wave driven. A pseudo ground swell, 6
to 8 second periods, in time may develop due to a decent fetch
with these onshore winds to operate over.

LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 300 PM Saturday...Complex low pressure system will track
NE parallel and near to the Carolina/VA coast Tues into Wed. A
strong onshore flow will persist into Tues , but winds will
diminish as they shift around from on shore to off shore by Wed
on the back end of the low as it lifts off to the northeast.
Another system will follow behind this one, dragging a cold
through on Thurs. Therefore expect off shore flow to continue
through much fo the period.

Overall, expect seas to subside through the period from a peak
Tues morning, above 10 ft in outer waters. The on shore flow
will shift around to the off shore and decrease with seas down
below SCA thresholds by Wed morning and continuing to lower to 2
to 4 ft by Thurs morning.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Gale Watch from Monday afternoon through Tuesday morning for
     AMZ250-252-254-256.
     Small Craft Advisory from 5 AM to 3 PM EDT Monday for AMZ250-
     252-254-256.

&&

$$
SYNOPSIS...DCH
NEAR TERM...III
SHORT TERM...DCH
LONG TERM...RGZ
AVIATION...III