Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 291139
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
739 AM EDT Thu Jun 29 2017

.SYNOPSIS...
It will be dry today, but showers and thunderstorms will return
Friday and then remain in the forecast each day, mainly during
the afternoon and evening hours. Summertime heat and humidity
will return for the weekend, becoming hot next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Thursday...High pressure will drift farther off the
NC/VA coast today while weak 5h ridge over the western Atlantic
slowly expands northwest. Low level flow will be southerly from
the get go but flow aloft will have more of a westerly
component into this evening before flow aloft starts to back to
the southwest. Increasing low level moisture may lead to a bump
in cloud cover this afternoon but the strength of the subsidence
inversion and the presence of dry air above 7k or 8k ft will
not support any precipitation. Backing of the flow aloft this
evening and overnight does bring about a period of deeper
moisture return, which will continue beyond the end of the
period. Winds aloft back as a result of the 5h ridge retreating
ahead of approaching shortwave, but do wonder if this is all
happening a bit too quickly in the guidance. Would not be
uncommon for the 5h ridge to linger longer or for the shortwave
to be a little weaker than expected. As such will stay on the
lower side of the pop guidance with only slight chance to low
chance creeping in from the southwest late in the period.
Temperatures will be close to normal with highs in the mid to
upper 80s and lows in the upper 60s to lower 70s.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 300 AM Thursday...It will become warmer and more humid
during this period with the risk for thunderstorms returning.
High pressure off the Mid-Atlantic and mid-level ridging will
increase heights with 850 mb temps climbing to 17C on Fri and
19C on Sat. Highs in the mid 80s Fri will increase to the upper
80s and lower 90s Sat. Heat index values will be around 100
degrees on Sat. Lows will be in the 70s, mid and upper 70s Sat
night.

As the ridge amplifies offshore, moisture gets channeled into
the eastern Carolinas which increases precipitable water values
to 2 to 2.25 inches. A trough coincident with a significant mid-
level shortwave lifting across the area Fri should allow for
scattered to perhaps numerous showers and thunderstorms. A
weaker impulse aloft on Sat combined with strong heating should
also allow for at least scattered thunderstorms. Forcing looks
stronger for convection on Fri while instability should be higher
on Sat.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 300 PM Wednesday...After the cool weather of the last couple
of days, summer heat and humidity should come roaring back next
week. Persistent upper level ridging across Florida and the Gulf
Coast and the Bermuda High offshore will allow heat and humidity to
build through the period. A time-series plot of forecast 850 mb
temps shows +17.5C Sunday, and +18C Monday through Wednesday.
The ECMWF actually has some forecast 850 mb temps near +20C by
Wednesday, however we`ve noticed over the past several years
there is a summer warm bias in the ECMWF at the extended range.

The airmass should be moderately to strongly unstable through the
period with CAPE values rising to 2000-3000 J/kg each afternoon.
West to northwest flow aloft, a pinned seabreeze near the coast, and
a well-defined Piedmont trough (perhaps evolving into an inland
thermal low for a few days next week) should set the stage for
scattered diurnally-driven storms each day. Precipitable water
values will fall to around 1.8 inches early next week.

Afternoon highs in the 90s and dewpoints in the lower 70s will
bring heat indices to 100 to 103 degrees in most locations away
from the beaches each day next week.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
As of 12Z...VFR will continue into tonight with surface high to
the northeast providing onshore flow. Sea breeze will make its
way inland with some cumulus clouds developing along it. No
rainfall is expected, but marginal increase in low level
moisture will lead to some potential for MVFR or even IFR
ceilings as the forecast period comes to an end Fri morning,
especially at KILM and KCRE.

Extended Outlook...Brief MVFR/IFR possible in and near diurnal
driven convection starting Friday. Brief morning MVFR/IFR
possible from fog or low stratus between 08-12Z starting Sat.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Thursday...Light northeast to east flow this morning will
steadily veer to east-southeast today as surface high moves farther
off the NC/VA coasts. Gradient will remain weak with onshore flow on
the low end of the 10 to 15 kt range. Onshore flow continues
overnight but speeds drop under 10 kt as the gradient relaxes with
the loss of daytime heating. Extended period of onshore flow will
lead to 2 to 3 ft seas becoming predominantly 3 ft later today and
tonight.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 300 AM Thursday...Wind speeds will be increasing during
this period, but are expected to remain below Small Craft Should
Exercise Caution criteria. Wind speeds will be 10 to 15 kt Fri
and Fri night increasing to 15 to 20 kt during Sat and through
Sat night as a thermal trough helps to tighten the gradient. The
wind direction will be SE to S on Fri, becoming SW beginning
Fri night. Seas will be 2 to 3 ft, building to 3 to 4 ft later
Sat and Sat night.

LONG TERM /SUNDAY THROUGH MONDAY/...
As of 300 PM Wednesday...Bermuda high pressure well offshore
will extend its ridge axis westward across Florida and into the
northern Gulf of Mexico Sunday and into early next week. With
the ridge remaining south of the area, mainly southwesterly
winds are expected through the period with the typical afternoon
seabreeze backing wind directions more southerly with an
increase in wind speeds.

With inland highs in the 90s and westerly winds aloft, there should
be scattered thunderstorms making their way down to the beaches and
offshore virtually every afternoon. Average sea heights of 2-3
feet are expected.

&&

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

&&

$$

NEAR TERM...III
SHORT TERM...RJD
LONG TERM...TRA
AVIATION...RJD



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