Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Wilmington NC
131 am EDT Wednesday Apr 16 2014

Synopsis...
in the wake of a strong cold front...chilly high pressure will wedge
across the area Wednesday and then slowly weaken by Friday. Low
temperatures through Wednesday night will be in the 30s and near the
freezing mark for some locations well inland early Thursday morning.
Conditions will deteriorate in advance of a cold front that will
move into the area and stall early next week.

&&

Near term /through tonight/...
as of 130 am Wednesday...high pressure is rapidly building into the
region this morning. The clearing line is making steady progress
to the southeast. The main issue for the near term remains low
temperatures Thursday morning. The latest guidance has trickled in
with little change with the GFS/mav numbers cooler and more
importantly below freezing in Lumberton. With the boundary layer
remaining mixed...although not to the extent we are seeing this
morning...I still like the warmer NAM/met numbers. Long story
short...I am not issuing any frost or freeze advisories or
warnings. I do think it would be prudent to issue an Special Weather Statement in the
northwestern counties to further emphasize the caveats/threats is
the GFS numbers do verify.

&&

Short term /Thursday through Friday night/...
as of 300 PM Tuesday...winter to make one final (hopefully)
return to the area Wednesday as a wedge of high pressure builds
down the coast behind tuesdays cold front. While the short term
will be dry and mostly sunny...well below normal temperatures and gusty
winds will make it feel more like January than April...especially
on Wednesday.

With no significant weather of which to speak during mid-week...the
short term is primarily a temperature forecast. Guidance continues
to indicate that highs on Wednesday will remain sub-60 (approaching
record low highs). It is very difficult to keep highs below 60 this
time of year in the eastern Carolinas...especially without true and
strong cold air advection in place. While NE winds will be gusty on Wednesday...and
back trajectories show the air mass originating from central
Canada...full middle-April sun and middle-level thicknesses which actually
rise through the day would favor at least slightly warmer temperatures. In
fact...1000-850mb thicknesses climb from around 1290m (supportive of
snow!) To 1320m by the Wednesday night. Although this will be offset by a
very shallow cold dome and weak mixing...will bump highs a bit on
Wednesday from inherited. Still expect highs to be sub-60 across the
northern tier...with low 60s in the southern Pee Dee and South
Santee River basin. Gusty NE winds around the strengthening surface
wedge will make it feel even cooler through the afternoon. Air mass
modification will allow temperatures to rebound more significantly on
Thursday...with highs reaching well into the 60s. This is still
below normal...but much more reasonable for mid-April.

The lows Wednesday night will be very cold...and will approach
record values for the date. MOS bulletins suggest lows dropping to
freezing or below across the western half of the County Warning Area...with middle 30s
at the coast. This would approach or set records:

Record lows for Thursday morning 4/17:
Wilmington, NC - 34
Florence, SC - 33
North Myrtle Beach, SC - 32

However...expect it would take ideal radiational cooling or strong
cold air advection to drive temperatures to freezing...neither of which will be in place
Wednesday night...and in fact some moisture advection off the ocean
may create some enhanced stratus/stratocu Wednesday night which
would further inhibit cooling. Nonetheless...Wednesday night will be
extremely cold for this time of year...with widespread middle 30s
likely. Although this will prevent the necessity for any freeze
products...frost is possible. However...winds are expected to remain
elevated through the night...so no frost is currently anticipated.
Thursday night will also be chilly...but 5-10 degrees warmer than
what is expected Wednesday night.

&&

Long term /Saturday through Tuesday/...
as of 300 PM Tuesday...weakening high pressure over the region on
Friday. Middle level trough axis swings through and develops trough of
low pressure off the coast. This should spread ample cloud cover
across most of the region and perhaps low rain chances long the
coast. Dry air pushes in from the northwest Friday night as will middle level
negative vorticity advection due to the exiting shortwave. Dampening middle level ridge builds
in from the west over the weekend followed by a shortwave on Monday.
The weekend looks dry and seasonable and some rain chances will
return with the upper disturbance for Monday...possibly lasting into
Tuesday.

&&

Aviation /06z Wednesday through Sunday/...
a cold front has cleared all terminals and skies have
become scattered. North winds will gust to around 25 knots early this morning
..with wind directions becoming NE after sunrise. Winds gusts will
decrease in the middle afternoon at kflo/klbt and late afternoon/early
evening at the coastal terminals. Low VFR level clouds will be
increasing along the coast in the evening...but confidence is low
that MVFR ceilings will occur.

Extended outlook...periods of MVFR ceilings late Wednesday evening
through early Saturday...with low confidence of IFR stratus ceilings
each morning. VFR Saturday afternoon into Sunday.

&&

Marine...
near term /through tonight/...
as of 130 am Wednesday...Small Craft Advisory continues for all waters
through the period. Winds gradually back off from this mornings
values of 25-30 knots...a bit higher than expected and from the
north to northeast of 15-20 knots by the end of the period. Seas
will keep the advisory intact. This mornings values of 3-8 feet will
drop to 4-6 feet late.

Short term /Thursday through Thursday night/...
as of 300 PM Tuesday...strong wedge of high pressure building
down the coast on Wednesday will persist through the short
term...creating gusty NE winds through most of the period.
Strongest winds will be early Wednesday...when winds veer from
north to NE at 20-30 kts. These winds will remain NE through the
rest of the period...with slowly decreasing speeds to 10-15 kts
Thursday night. Waves will be driven primarily by a north/NE wind
wave...with amplitudes of 5-8 feet Wednesday falling to 4-6 feet
Thursday. The exception will be in the typical wave-shadow region
SW of Brunswick County where NE winds get blocked...and thus wave
heights will be just 1-3 feet locally in the near shore portions of
amz252 and amz254. The Small Craft Advisory has been extended
through all of Thursday...and may need further expansion into
Friday with later updates.

Long term /Friday through Sunday/...
as of 300 PM Tuesday...a northerly component will be found in the
forecast for the duration of the period. Initially it will be
northeasterly on Friday as the forecast zones lie between high
pressure over land and a surface trough well offshore. This may
lead to enough of a gradient pinch for some advisory-worthy 6 feet
seas but they should be short lived as both features will be in a
weakening state. Saturday brings a renewed push of high pressure
into the middle Atlantic and southeast but the coastal trough will no
longer be a player. This backs the flow a bit to northerly. As the
center of the high moves east into Sunday local winds will veer
back to northeasterly.

&&

Ilm watches/warnings/advisories...
SC...none.
NC...none.
Marine...Small Craft Advisory until 5 PM EDT Thursday for amz250-252-
254-256.

&&

$$
Synopsis...shk
near term...shk
short term...jdw/bjr
long term...mbb
aviation...mrr
marine...