-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KILM 230528
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
128 AM EDT Tue May 23 2017

.SYNOPSIS...
Waves of low pressure will develop along stalled cold front
producing increased chance of showers and thunderstorms through
mid week. A cold front trailing from a deep low pressure system
over the Ohio Valley on Thursday will push through bringing the
final round of storms to the area. High pressure will build in
on Friday maintaining quieter weather for much of the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1000 PM Monday...Widespread thunderstorm activity over the
past 6-8 hours has left a chaotic low-level wind and pressure
pattern across the eastern Carolinas. A synoptic front is
stalled back in the NC and GA mountains, while here closer to
the coast a convective outflow boundary has sunk to a position
10-20 miles off the coast of Cape Fear, Myrtle Beach and
Georgetown, SC. Synoptic south-southwesterly wind should
overwhelm this boundary over the next 3-4 hours, with the
current northerly winds observed along the coast and offshore
veering back to the south again late tonight.

Aloft, conditions are warm and very moist with deep southwesterly
flow advecting rich Gulf moisture overhead. Precipitable water
values are approaching 2.00 inches, and the 00Z Charleston, SC
weather balloon revealed a potential warm-cloud layer nearly
12,000 feet deep. The depth of saturated above-freezing
atmosphere has been shown to be an excellent predictor of heavy
rain potential.

Our first big wave of convection dropped a widespread 0.5 to 1.0
inch of rain across all but the immediate coast, with some
embedded spots where radar and MRMS multi-sensor estimates are
as large as 4.6 inches. A second wave of showers and t-storms
currently across eastern Georgia should move up the coast
overnight bringing another round of good rain. With plenty of
elevated instability lingering overnight (500-1000 J/kg)
forecast PoPs remain 80-100 percent with an additional 0.3
inches of rain inland and up to 1+ inch along the coast
expected.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
As of 300 PM Monday...Front remains stalled in the area Tue
night, moving a little closer to the coast by Wed morning.
Although moisture will be on the high side there will be a lack
of upward motion. In fact there may be a lull as the passage of
a surface wave Tue evening and its associated shortwave will
lead to a period of subsidence Tue night. Forecast soundings
depict this rather well showing a mid level subsidence inversion
developing and precipitable water values dropping close by as
much as 0.50 inch overnight. Mid level trough axis remains well
west of the area Wed which will keep the front lingering in the
region. Passage of the surface wave Tue night may briefly push
the front south of the area early Wed but it is quick to return
north as a warm front around midday Wed.

Better rainfall chances develop later Wed and Wed night as potent
shortwave dropping into the 5h trough early Wed helps kick the mid
level pattern in motion. The 5h trough rotates east-northeast Wed
into Wed night, driving a stronger cold front into the region Wed
night. Increasing southwest flow ahead of the front, as well as
strengthening low level jet, increases deep moisture in the region.
Pwats rise to near 2 inches Wed afternoon and evening and mid level
lapse rates steepen. PVA ahead of advancing shortwave, strong
divergence aloft, and the abundance of moisture coupled with low
level dynamics should yield a healthy line of convection Wed
afternoon and evening. Although severe parameters are not
particularly high there will be at least some potential for severe
weather given the strengthening low level jet and modest shear.
Large dry slot sweeps in late Wed night as the trough axis moves
east, ending any precip prior to daybreak Thu. Cold front likely to
be moving into the region as the period ends so cooler and drier air
will not arrive until after the end of the period. High temperatures
will continue running below climo with lows above to well above
climo due to clouds and moisture.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 300 PM Monday...Deep frontal moisture to be offshore by the
start of the period. However the main trough axis and strongest
shortwave will be crossing the area and this should manage to
squeeze a few light and short-lived showers. Continued dry advection
and the lifting of the trough Thursday night should keep us dry
despite one last final and moderately strong vorticity center
streaking by. Zonal flow will keep the weekend dry and fairly
seasonable with only gradually increasing surface dewpoints.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
As of 06Z Tuesday...Challenging conditions for the aviation
community the next 24-36 hours and maybe beyond. For the near
future, expect MVFR conditions area wide with some intervals of
IFR mingled in as areas of showers and thunderstorms move
through occasionally. During the next six to eight hours inland
sites have the highest chances of IFR and have addressed with
TEMPO groups through about 15 UTC. A little more iffy at the
coast as another round of showers and thunderstorms move across
which oddly enough keeps the boundary layer a little more active
somewhat precluding fog and persistent lower ceilings. The best
chance of widespread IFR conditions is late tonight in the wake
of another round of convection when a weak surface pattern is
left behind to work with all the low level moisture.

Extended Outlook...Reduced flight categories will be possible
in periodic showers and thunderstorms through Thursday. The
strongest convective activity should occur Wednesday.
-- End Changed Discussion --

&&

.MARINE...
NEAR TERM /THROUGH TUESDAY/...
As of 1000 PM Monday...Showers and thunderstorms did indeed move
out across the coastal waters this evening. The rush of cool
northerly winds along the front edge of these storms has acted
like a miniature cold front and has reached 10-20 miles from
shore. This boundary should stall over the next couple hours,
then should get overwhelmed by the synoptic southwesterly wind
overnight. Winds should increase to SW 10-15 knots by 2-3 AM
with gusts to 20 knots possible along the South Carolina coastal
waters late.

Another wave of showers and thunderstorms currently observed
across eastern Georgia should move north along the coast
overnight, bring more rough conditions for mariners from
Georgetown through Myrtle Beach and Cape Fear. Reduced
visibility in heavy rainfall and frequent lightning may
redevelop late tonight.

Seas currently 2-3 feet consist of a mix of 9-second swell and
4-5 second wind waves. Sea heights may drop half a foot or so in
the next couple of hours, but should begin to build back up late
tonight in the increasing southwesterly wind.

SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 300 PM Monday...Front remains west of the waters through
the period, maintaining southwest flow. Speeds start to increase
later Wed and Wed night as the front moves to the coast and
slowly strengthening low moving into the OH valley helps tighten
the gradient. Southwest flow on the high end of the 15 to 20 kt
range Tue night will increase to a solid 20 kt around midday
Wed with 20 to 25 kt expected late Wed and Wed night, likely
requiring SCA headlines for all waters. Seas will build due to
prolonged and increasing southwest flow. Seas 4 to 5 ft at the
start of the period will build to 4 to 6 ft during Wed,
eventually reaching 7 ft Wed night.

LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 300 PM Monday...Small Craft Advisory will be in effect on
Thursday just ahead of a cold front that will pinch the
gradient. Within the agitated wind field of the pinched gradient
a strong upper disturbance will traverse the area possibly to
enhance wind gusts. In the wake of this boundary there will be
west winds to round out the period of gradually diminishing
speed. Wave heights will similarly abate somewhat slowly.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
SC...Beach Hazards Statement from 7 AM EDT this morning through
     this evening for SCZ054-056.
NC...Beach Hazards Statement from 7 AM EDT this morning through
     this evening for NCZ106-108.
MARINE...None.
-- End Changed Discussion --

&&

$$
SYNOPSIS...RGZ
NEAR TERM...TRA
SHORT TERM...III
LONG TERM...MBB
AVIATION...SHK
MARINE...