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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KILM 221311
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
911 AM EDT Thu Jun 22 2017

.SYNOPSIS...
Bermuda High pressure will build westward over the Eastern
Carolinas through today as Tropical Storm Cindy moves up from
the western Gulf coast. The remnants of Tropical Storm Cindy
should reach the southern Appalachians Friday night with its
associated moisture increasing the risk for showers and
thunderstorms through Saturday. A cold front will reach the
area but may remain stalled in close proximity Sunday and
Monday. Dry High pressure will build in through the middle of
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 915 AM Thursday...Analysis of morning sounding data and
latest high-res guidance confirms earlier forecast reasoning.
High P/W values today at around 2 inches and a moderately
unstable airmass will make for isolated to widely scattered
convection, mainly this afternoon. Triggers will be few and far
between, with the afternoon sea-breeze circulation being the
primary and initial one. Extensive cloud cover will limit highs
to the upper 80s most places. Previous discussion follows:

This will be the last day of the moisture feed from Tropical
Storm Cindy as the storm moves on shore over the TX/LA border.
Some mid level drying behind trough aloft produced some breaks
in the clouds overnight but moisture profiles continue to show
moisture just above h70 which was maintaining mostly cloudy
skies over the region. Other shallow moisture will produce some
low clouds but these should lift into strato cu through the
morning. Any nocturnal showers will be steered off to the east
and should remain mainly off shore overnight.

Atlantic ridge will build back west over the Eastern Carolinas
through today into tonight, but some shortwave energy riding
around the western periphery of the ridge will move up from the
S-SW over the Carolinas. An area of associated clouds and pcp
was visible on the Satellite/Radar and although this will mainly
remain west of the the local forecast area, there will be some
energy riding over the Eastern Carolinas this aftn. Overall the
moisture will increase through the mid levels again through
today from convection upstream, but also expect some
convergence along western periphery of ridge as it builds back
in and minor convection focused along sea breeze boundary.
Therefore expect a decent amount of clouds once again today, but
with a warm start to the day, some breaks in the clouds and
westerly downslope flow, temps will reach into the mid 80s most
places. The HRRR shows mainly iso to sct showers developing
especially along sea breeze in SC. This is where I kept the
highest pops in the scattered range. Pcp water values remain up
near 2 inches, but a lot of the moisture will remain above h70
with mainly clouds around the forecast area.

By tonight any shortwave energy will move north with ridge
building over the Carolinas leading to some subsidence and drying.
Although expect some mid level clouds to hang on and most of
the deep layer drying to occur heading into Fri. Overnight lows
will be the mid 70s once again. May see some stratus around
again, but will keep pcp out of forecast.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 300 AM Thursday...The 500 mb ridge near the Florida east
coast for the past few days will get displaced eastward late
this week as the remnants of Tropical Storm Cindy move across
Virginia Saturday morning, followed by a pair of shortwave
troughs in the Great Lakes which drop 500 mb heights even along
the Southeast coast.

With the deep flow of Gulf moisture cut off by Cindy`s northward
movement out of the Gulf, drier air is expected to advect overhead
at and above the 900 mb level Friday. Precipitable water values
around 2 inches today should fall to 1.6 to 1.7 inches by Friday
afternoon, with forecast soundings showing the tell-tale bump of a
weak subsidence inversion from the nearby upper level ridge. There
will still be enough surface moisture present Friday for CAPE values
near 2000 J/kg, and a slight chance of thunderstorms will remain in
the forecast.

The remnant circulation of Tropical Storm Cindy will move eastward
through Virginia Saturday morning, veering our deep layer wind
direction more westerly with time. A pinned seabreeze boundary plus
natural differential heating boundaries associated with soil type
changes in the Sandhills should be enough to fire scattered showers
and storms. Storm motion should be west to east at a rapid 25 mph.
The better chance of rainfall might hold off until Saturday night as
the surface cold front trailing behind Cindy`s remnants finally dips
down into the Carolinas.

It`s interesting to note that over the past 20 days there have been
some consistent MOS biases evident with high temperatures across the
area. Most notably, both GFS and NAM MOS have been 2-3 degrees too
warm at Florence, SC, with a 1 to 1.5 degree warm bias also noted at
Lumberton, Whiteville, and Myrtle Beach (MYR). Recent rainfall
amounts have not been large enough to produce cool/wet soil
anomalies, so I`m not sure what the reason is for this clear bias.
However, my forecast highs Friday and Saturday remain on the low
side of MOS at these sites.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 300 PM Wednesday...Potentially very unsettled through the
period but lots of uncertainty exists even in the first part of the
extended.

A cold front should be just along or off the coast by early
Sunday. The caveat to this is that while the front tries to push
east, the mid- level pattern features an amplification of the
ridge across the east, thus slowing and stalling the front.
Where this front stalls will be key to the Sun/Mon forecast. The
GFS stalls this front along the coast with continued showers
and storms due to deep SW flow and overrunning, and potentially
secondary low development. The ECM/CMC push the front far enough
offshore to create dry weather the latter half of the wknd.
Climatologically the stalled boundary makes sense, and is
supported by WPC progs, so will maintain the inherited unsettled
forecast into early next week with temps cooling to below climo
after a very warm Saturday.

Anomalously deep longwave trough then digs into the east clearing
the front and bringing much cooler temperatures to the region. 850mb
temps may drop towards 10C by the middle of next week, which is
below the 10th percentile for late June, suggesting highs and lows
several degrees below climo along with a much drier and refreshing
airmass.

&&

.AVIATION /13Z THURSDAY THROUGH MONDAY/...
As of 12Z...Mid-level cloudiness should be the rule today, with
lower cumulus (bases 2500-4500 feet AGL) popping up beneath as
very humid air near the surface begins to rise in daytime
thermals. Some low stratus clouds with bases 400-700 feet AGL
exist across the interior Coastal Plain affecting the Florence
(FLO) and Lumberton (LBT) airports currently, but this should be
a relatively brief phenomena, dissipating between 13-14Z.

Afternoon showers and storms should be scattered in coverage
and are not currently included in forecasts prior to 21Z. The
potential for storms is only 30 percent, probably concentrated
along the seabreeze boundary developing west of the coastal
airports around 18-20Z. Any lingering convective activity
should dissipate around 00Z with mid-level ceilings continuing
tonight.

Extended Outlook...MVFR ceilings/vsbys Saturday as tropical
moisture associated with Cindy remnants traverse the region.
Patchy fog and low ceilings possible 08z-13z Friday. More
MVFR/IFR conditions possible in SHRA/TSRA with passage of cold
front late Saturday into early Sunday.

&&

.MARINE...
-- Changed Discussion --
NEAR TERM /THROUGH TONIGHT/...
As of 915 AM Thursday...Latest obs show light southerly winds
with seas of 2 to 3 ft. Forecast on track with no changes
needed. Previous discussion follows:

Benign marine conditions will continue through today as high
pressure builds back westward over the waters. A more westerly
wind this morning behind low level trough/remnant sfc boundary
will come back around to the S-SW as Bermuda High builds
westward. Wind speeds generally 10 kt or less will increase by
tonight into early tomorrow as gradient tightens between Bermuda
High and Cindy moving up from the Gulf. Therefore seas 2 to 3
ft through today will increase up to 3 to 4 ft as winds increase
up to to 10 to 15 kts through tonight.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 300 AM Thursday...Bermuda high pressure anchored well off the
Carolina coast will struggle to maintain its grip on our weather as
a cold front and the remnants of Tropical Storm Cindy approach from
the west. Cindy`s low should link up with the cold front across
Arkansas and western Tennessee Friday, accelerating eastward across
Virginia Saturday morning. This will help increase our wind speeds
here both Friday and Saturday, with an increasing potential of Small
Craft Advisory conditions developing before sunrise Saturday morning.

After Cindy`s remnant low exits the Mid-Atlantic coast by Saturday
afternoon, the trailing cold front should sweep through the
Carolinas late Saturday night, likely not reaching the beaches until
Sunday morning around daybreak.

LONG TERM /SUNDAY THROUGH MONDAY/...
As of 300 PM Wednesday...Cold front will waver in the vicinity
Sunday and Monday before finally pushing offshore late in the
period. This will create a weaker gradient and wind speeds
around 10 kts, with direction varying from S to W at times.
After the seas will continue to drop to just 2-3 ft late Sunday
and remain at these amplitudes on Monday.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...RGZ
NEAR TERM...REK/RGZ
SHORT TERM...TRA
LONG TERM...JDW
AVIATION...TRA
MARINE...REK/TRA/RGZ