Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 281422
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1022 AM EDT Sun May 28 2017

.SYNOPSIS...
High pressure well southeast of the Carolinas will provide hot
weather today and Monday. Thunderstorms could become more
frequent as a weak front arrives from the north and stalls
nearby Wednesday through Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM Sunday...Forecast (mostly high resolution)
guidance still showing mixed signals for the evolution of
expected convection this afternoon. It appears more of a timing
issue and if anything the start is a bit later than previously
advertised. I still like the GFS solution with a remnant vort
in upstate Carolina associated with a previous MCS slated to
cross what will be a fertile instability ground later this
afternoon at a window between 19-22 UTC. Recalling events of
yesterday in Tennessee, thats when things got going and
translate that eastward, it all seems reasonable. Long story
short, no changes to the forecast with the mid morning update.
SPC continues to keep all of our North Carolina counties in a
slight risk clipping some of the northern South Carolina
counties. Previous discussion follows:


Complex situation evolving today creates a
more than challenging forecast, with heat and tstms possible across
the area.

Even before addressing Sunday`s weather, analysis of the ongoing
situation must be completed. A complex of tstms moving through the
western Carolinas is the last surviving trace of what was once a
powerful MCS. This complex has weakened both due to loss of heating,
but also advection into drier and more stable air as noted on SPC
mesoanalysis. While one moderately sized cluster of storms continues
to produce across western/central NC, this will likely remain north
of the ILM CWA thanks to 0-6km mean winds on the GSO U/A sounding
and KRAX VWP almost directly from 270 degrees. Do not anticipate
convection locally overnight, but debris cloudiness will be
widespread into daybreak.

Synoptic setup for Sunday is quite similar to Saturday, although
minor details create a more challenging, and possibly more active,
forecast. Elongated high pressure along the Gulf Coast will
gradually advect east and amplify, with mid-level heights climbing
slowly this evening and tonight. To the north, a belt of enhanced
mid-level westerlies will persist between this ridge and a series of
troughs moving through southern Canada. Within this belt, vorticity
impulses will move quickly from west to east, with each one creating
the potential for convection beneath it. The challenge today then,
is when will these vort impulses create tstms, and where will they
occur.

Once again, a mid-level cap will be present today, and as the mid-
level ridge amplifies late, it will actually increase in intensity.
However, this likely occurs too late to prevent subtle height falls
within the flat ridge this aftn/eve, and the 850-700mb thermal ridge
is noticeably weaker than what was present on Saturday. This
suggests that convection is more likely today, especially as
guidance is in good agreement with timing of a vort moving overhead
during late aftn/eve /peak heating./ The environment will be very
supportive of tstms this aftn, assuming the cap is not stronger than
currently progged, and subsidence behind the current vort isn`t too
strong to squelch lift. Big caveats of course, but forecast profiles
suggest very strong MLCAPE of 2000 J/Kg thanks to highs around 90
with dewpoints around 70, and very steep ML lapse rates. As this
vort moves to the north, storms may grow upscale into another tstm
complex thanks to 0-6km bulk shear of up to 40 kts, and this is
shown in varying degrees on the latest HRRR/ARW/RUC. SPC has placed
SE NC into a SLGT risk today, with MRGL across NE SC for this
potential. Large hail and damaging winds are the most likely threats.

That being said, do NOT expect widespread severe weather today. A
cluster of fast moving storms is possible, mostly across NC
counties, but total coverage may end up being isolated to widely
scattered. Differences in timing, subsidence, and the aforementioned
cap all produce enough uncertainty to cap POP at 40 percent well
north, with just SCHC south of the state line. Convection that does
develop will likely move offshore or dissipate during the evening,
leaving slightly drier air and another lull in convection tonight.
Debris cloudiness and continued warm WSW winds will keep mins very
warm however, falling only into the 70-74 degree range, warmest at
the coast.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...A 500 mb ridge centered over Florida
Monday will strengthen as it edges offshore Monday night into
Tuesday. Although models still have some disagreement with
specifics, it appears the seemingly never ending trail of upper
level disturbances will remain just north of our portion of the
Carolinas Monday through Tuesday, sparing us the worst of what
could be multiple periods of severe weather across western South
Carolina and most of North Carolina.

Monday appears to be the hottest day of the week as 850 mb temps
climb as high as +19C. Plenty of sunshine should push highs well
into the 90s away from the beaches. Our latest forecast of 94 in
Florence is just one degree away from a record of 95 set in
1991. Enough westerly low-level wind should exist to delay the
seabreeze by a couple hours and pin the boundary near the coast.
Dewpoints in the lower 70s near the coast should push heat
indices near 100 degrees in spots.

Forecast thunderstorm chances Monday range from around 10
percent in Georgetown to 30 percent in Lumberton. This is due
to an increasingly substantial cap of warm mid-level air as you
travel southward closer to the upper level ridge, and also
increasing distance from the wavetrain of upper disturbances
which sets up from central MS/AL across western SC into NC.
Although thunderstorms should be only isolated in our portion of
the Carolinas, steep lapse rates above the subsidence
inversion, mid-level westerly winds of 30-40 knots, and plenty
of dry air aloft means any storms that do form could produce
damaging winds and hail.

On Tuesday the upper ridge nudges just a bit farther off the
Florida coast, allowing the wavetrain of disturbances to shift a
little eastward as well. High temperatures should run several
degrees cooler with a convectively-overturned airmass arriving
from the west that should feature 850 mb temps only +15C to
+16C, about 3 degrees C cooler than Monday. This should
translate to highs mainly upper 80s to near 90. The threat for
scattered thunderstorms with strong winds Tuesday afternoon may
linger into the night.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 300 PM Saturday...The mid level pattern will show more
amplitude across the Eastern U.S. with a broad trough at least
initially dipping into the Ohio Valley with ridging off to the
southeast. This will keep the pattern somewhat unsettled with
ample moisture and several shortwaves. Differences in the global
solutions as to timing of course but reconciling the various
solutions yields the highest pops, at least for this package
occurring Tuesday and once again Friday and Saturday when the
mid level flow weakens considerably with an old baroclinic zone
providing an impetus for activity oriented east to west. No real
fronts pushing through to provide any appreciable airmass
change with highs and lows maintaining levels a couple of
degrees above average.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
As of 12Z...VFR conditions will continue through at least mid-
afternoon (19Z) before possible scattered thunderstorms develop.
Warming inland temperatures should help develop a seabreeze
near the coast between 16-18Z with winds at CRE and MYR turning
south-southwesterly at 12-15 knots with gusts approaching 20
knots. Any afternoon/evening thunderstorms will have the
capability of producing strong winds and frequent lightning. The
upper level disturbance that may develop these storms should
sweep off the coast between 03-05Z tonight with VFR conditions
developing overnight.

Extended Outlook...MVFR/IFR conditions are possible in showers
and thunderstorms Monday Night through Tuesday. More typical
summertime scattered showers and thunderstorms are possible
Wednesday and Thursday.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM Sunday...Summertime pattern is steady state and
warrants no updates to the forecast with the mid morning update.
Previous discussion follows:

Elongated high pressure along the Gulf Coast
will maintain its local influence across the waters today. Winds
from the SW will slowly intensity today, from 10-15 kts this
morning, to 15-20 kts this evening and tonight. These persistent and
increasing SW winds will create a 5 sec SW chop which will mask the
continuing but low-amplitude SE swell, and seas of 2-4 ft are
forecast through the period. A cluster of showers and thunderstorms
may move in the vicinity of the waters this evening with the
potential for gusty winds and hail, but confidence is low attm.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...High pressure centered south of Bermuda
will control our weather through the Monday-Tuesday timeframe
with west-southwesterly winds. As it typical this time of year,
large inland-to-offshore temperature contrasts should produce
well-defined seabreezes both days with wind gusts near the
beaches reaching 20 knots from mid-afternoon through early
evening. Otherwise wind speeds of 10-15 knots should prevail
through the period. Isolated thunderstorms will be possible as a
series of weak upper level disturbances move across North
Carolina.

LONG TERM /WEDNESDAY THROUGH THURSDAY/...
As of 300 PM Saturday...Its mostly a show of Bermuda High
pressure and a summertime pattern with a south to southwest flow
through the period. There may be some local and temporary
distortion of wind fields due to expected convection but the
overall synoptic pattern should remain the same. Significant
seas will be 2-4 feet.

&&

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

&&

$$
SYNOPSIS...TRA
NEAR TERM...JDW/SHK
SHORT TERM...TRA
LONG TERM...SHK
AVIATION...TRA
MARINE...


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