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Area forecast discussion 
National Weather Service Wilmington NC
409 am EDT Wednesday Jul 27 2016

Synopsis...
high pressure will expand across the Carolinas, maintaining
uncomfortable levels of heat and humidity this week. Isolated to
scattered showers and thunderstorms are possible each afternoon
and evening. The chances increase heading into early next week.

&&

Near term /through tonight/...
as of 415 am Wednesday...will go with a persistence type
forecast, using yesterday as the model day to work off of. Near
term models such as the hi-res WRF, the hrrr, and the rap all
indicate a repeat of yesterday with only isolated convection
possible along the sea breeze...and just north of the ilm County Warning Area
running from rah to mhx cwas. The outlier of those 3 models is the
hi-res WRF where it paints a possible cluster of storms along the
ilm to Fay line. At this point it seems too far south given the
strength of the upper ridge and the strength of the convective lid
and continued warm temps in the low and mid levels. Of note for
the ilm NC cwa, various model sounding data indicate 500 mb temps
slightly decrease to between -3 to -4.5 degrees c this aftn and
evening...and the subsidence inversion is not as strong or
prevalent. Again, this is mainly for the ilm NC portions. As
mentioned b4, will continue with persistence from yesterday and
not jump on the WRF bandwagon to increase pops.

For Max temps, stayed closer to the GFS MOS guidance and for lows,
stayed closer to the NAM MOS guidance. This based on the latest
verification for the ilm County Warning Area. The mid and upper 90s for highs
combined with low to mid 70s dewpoints yield heat indices in the
105 to 109 degree range. Even after the sea breeze pushes thru,
temps may drop to the 90-95 range but dewpoints will increase to
the upper 70s. This will not improve the heat indices, in fact,
it may actually make them worse. The heat advisory will run from
11 am to 7 PM today.

&&

Short term /Thursday through Friday night/...
as of 415 am Wednesday...ridging aloft and at the sfc will
dominate once again the ilm County Warning Area this period with the beginnings of
this ridge breaking down late Friday. The upper ridging and warm
temps aloft will again limit lapse rates and maintain a convective
lid across the fa this period, with weaknesses in this lid
occurring by Fri. Models indicate some decrease in progged 500mb
temps to -5 degrees c or lower by late Fri. However, the GFS still
indicates some remaining decent subsidence aloft and associated
inversion during Fri. Overall, will highlight a low chance pop
across the entire ilm County Warning Area on Fri, not just along and ahead of the
sea breeze which is highlighted on Thursday.

Heat advisories will be needed for both Thu and Fri. There is a
remote possibility that heat indices could breach excessive heat
warning criteria, which are heat indices 110 degrees or higher.
For daily Max temps, stayed closer to the GFS MOS guidance. And
for daily min temps, stayed closer to the NAM MOS guidance. This
is a carry over from the near term forecast with the reasoning
remaining the same.

Each day during the late evening thru pre-dawn hours, a low level
SW to west-southwest 20 to 30 kt jet will occur. This will keep a well mixed
sfc layer, in turn keeping fog development to a minimum, if any.

&&

Long term /Saturday through Tuesday/...
as of 415 am Wednesday...mid level heights will fall very slowly
through the period allowing and along with an increase in pws,
chance of convection will increase. Profiles for Saturday are
still somewhat unfavorable although there is plenty of moisture.
Mid level cooling along with similar moisture profiles increases
chances Sunday through Tuesday. We go from slight chance to just
under likely by Monday which continues through Tuesday. Regarding
temperatures, I really don't see much in the way of cold air
advection in the lower levels but more convection should shave a
couple degrees off the middle and upper 90s we are seeing now.

&&

Aviation /07z Wednesday through Sunday/...
as of 06z...persistence forecast will suffice as a mid level
ridge dominates the weather for the next few days and certainly
this taf cycle. VFR through the period. Some late day convection
did move across well to the north yesterday and may need
monitoring again late today but chances are slim.

Extended outlook...isolated to scattered afternoon convection
through Sunday may create brief periods of MVFR/IFR. Otherwise
expect VFR.

&&

Marine...
near term /through tonight/...
as of 415 am Wednesday...early this morning, the low level SW jet
will keep the SW winds busy across the ilm local waters. By
daylight mid-morning, these winds will slightly diminish to 10 to
15 kt. This afternoon thru mid-evening...the sea breeze will
provide an increase in winds near shore, with south-southwest at 15 kt with
gusts to 20 kt. The winds late this evening and overnight will
transition away from the sea breeze...to another low level jet
episode with SW winds mixing down to the ocean sfc. Significant
seas will basically run in the 2 to 4 foot range with locally
produced wind driven waves at 3 to 6 second periods dominating the
overall seas. Convection coverage, if any, will be isolated at
best.

Short term /Thursday through Friday night/...
as of 415 am Wednesday...the ridging from the sfc high will be
suppressed southward. This will increase the westerly component in
the wind directions during this period. The sfc pg will also
tighten slightly as a result of the ridge axis oriented further
south. In addition, the Carolinas sfc trof, Aka the Piedmont trof,
will Orient itself across the central and western portions of the
Carolinas this period. This will produce some tightening of the
sfc pg across the area waters this period. The daily inland
progression of the sea breeze may be limited due to the increase
in the westerly component of the winds...and their speeds during
this period. A daily nocturnal low level jet will again occur
during the late Thu evening through the pre-dawn hrs of Friday.
However, models indicate this will not be the case Friday night
and early Saturday.

Overall wind speeds will run in the 10 to 20 kt range with the 20 kt
mainly in the form of gusts. Significant seas will run 2 to 4 ft and
possibly 3 to 5 ft late Thursday night thru early Friday.
If the latter occurs, then a scec may be needed. Convection will
again be limited, with the best possibility occurring late Friday.

Long term /Saturday through Sunday/...
as of 415 am Wednesday...Bermuda high pressure along with the
inland Piedmont trough will be the main drivers of winds and seas
for the coastal waters. A south to southwest flow of 10-15 knots
will prevail with significant seas of 1-3 feet.

&&

Ilm watches/warnings/advisories...
SC...heat advisory from 11 am this morning to 7 PM EDT this evening
for scz017-023-024-032-033-039-053>056.
NC...heat advisory from 11 am this morning to 7 PM EDT this evening
for ncz087-096-099-105>110.
Marine...none.

&&

$$
Synopsis...shk
near term...dch
short term...dch
long term...shk
aviation...shk

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