Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
721 PM EDT sun Mar 9 2014
Spring-like weather will prevail through Wednesday ahead of a
middle-week low pressure system. A cold front will cross the eastern
Carolinas Wednesday evening...bringing chilly air into the region
Thursday into early Friday. Slight warming will bring seasonable
temperatures to the Carolinas next weekend.
Near term /until 6 am Monday morning/...
as of 7:00 PM Sunday...weak and dry cold front continues to slowly
drop southward across North Carolina. At the present rate it will
enter the forecast area this evening. It actually doesn't matter
too much whether it moves across the area or not as thermal
contrast is weak and there is no weather and few clouds associated
with this feature. Forecast for a cool and dry overnight period
remains unchanged. Previous discussion follows:
A fair amount of clouds moving across the coastal Carolinas as
weak dry cold front drops south. Model pcp water values show
concentrated moisture up close to an inch in band along and just
ahead of the front as it progresses south southeast through today.
Looking at sounding data and moisture profiles...this moisture was
mainly confined to the middle to upper levels. Although expect some
lower strato cumulus to develop as lift increases into early this
evening...but not enough to warrant any pcp. Models in fairly good
consensus bringing wind shift to northwest as front drops very slowly
south through this evening.
These clouds will slow the warming process...but with temperatures
already in the 50s by middle morning most places...and an increasing
downslope component to the wind...expect temperatures to rise into the
upper 60s most places. The clouds and slight cold air advection behind the front
this afternoon could offset the warming to prevent most temperatures to
remain below 70. Places across northeast South Carolina coast will
have the best chance as the front will reach there last as it slowly
progresses south. The westerly winds will help to keep any sea
breeze pinned along the coast keeping beaches cooler as water
temperatures remain near 50.
Dry air and subsidence will work its way into area through tonight
as nearly flat shortwave drops south and jet exits the area. This
will allow weak high pressure to build into the forecast area. Any
clouds will dissipate and the little push of cooler northerly
winds will drop out leaving clear skies and calm winds across the
area. This will provide some decent radiational cooling with temperatures
dropping a good 20 degrees. Not much in the way of moisture left
and therefore will leave out fog in forecast for now.
Short term /6 am Monday morning through Tuesday night/...
as of 3 PM Sunday...if you enjoy the Spring-like weather you may
consider invoking a 4-day weekend extending through Tuesday since
highs in the 70s are on tap both Monday and Tuesday...with 60s
closer to the immediate coast as refrigerated air remains poised
over the inshore waters with sea surface temperatures around 50 degrees.
Sunshine hours will remain high both days. Minimum temperatures
will be mildest Tuesday night into early Wednesday ahead of an
approaching frontal system. Very late in the short-term period
into the pre-dawn hours we bring a chance/slt chance showers as moisture
flux ramps up on SW trajectories aloft and offshore convergence
increases. Otherwise much of this period will be characterized by
moderate SW low-level wind flow...capped by dry west winds above
Long term /Wednesday through Sunday/...
as of 3 PM Sunday...period starts wet as two middle-level impulses
pass near the region. The first...southern stream shortwave...will
be moving offshore Florida Wednesday morning. The second...and more
impressive...northern stream shortwave will dig into the
middle-Atlantic by Thursday morning...and it is this impulse which
spawns a surface low pressure which will move northwest of the local area
on Wednesday. While column moisture increases Wednesday as evidenced
by precipitable waters exceeding one inch...still do not see a whole lot to drive
convective showers. As noted in previous forecast...subsidence
behind the departing southern stream impulse will somewhat offset
lift associated with the surface low...which in itself will be
strongest well northwest of the local area. The trend to continue high-chance
pop with low quantitative precipitation forecast remains...and wpc continues to back off on total
quantitative precipitation forecast for the event.
Wednesday will be warm...but cold front behind the surface low will
cause temperatures to crash by Thursday morning on strong cold air advection. 850mb temperatures
drop 10-15c during the overnight hours of Wednesday night...and lows by
Thursday morning will be 30 degrees cooler than wednesday's highs.
Continued but weakening cold air advection on Thursday will make Thursday much
colder. Still disagreement between the very cold European model (ecmwf) (highs in the
40s) and the not as cold GFS (highs in the mid-50s)...but the trend
continues downward and will adjust accordingly. Expect Thursday to
feature highs below typical early-January levels. Thursday night
will be the coldest night as the high sits overhead...and many areas
will fall below freezing.
Air mass modification begins Friday thanks to the middle-March
insolation...and by the weekend more significant warming will occur as
high pressure drifts offshore. Friday will remain below climatology...but
the weekend appears to feature climatology temperatures. GFS continues to insist
that a coastal trough will develop for the weekend bringing some
showers to the coastal sections of the County Warning Area...while European model (ecmwf) is dry. The
setup is typical of one which promotes coastal trough development so
will lean that way and introduce schc pop for the coastal zones
Aviation /00z Monday through Friday/...
as of 00z...expect VFR conditions this evening with winds becoming
light and variable soon after sunset. Mostly clear and calm
conditions overnight may allow for some br to develop after 06z...
especially along the coast where dewpoints have climbed late this
afternoon following sea breeze passage. Although the inland terms
are a bit drier...calm winds early this evening should allow for
good radiational cooling at kflo/klbt as well. Confidence is only
low to moderate at this time...but will maintain the possibility of MVFR
visibilities early Monday at all sites. Monday will be sunny with west-SW
winds at or below 8 kts...becoming S-SW around 10 kts after 18z at kcre/kmyr
as the sea breeze again pushes onshore.
Extended outlook...VFR will prevail through Tuesday. Chance of
showers/MVFR on Wednesday. VFR Thursday and Friday.
near term /through tonight/...
as of 7:00 PM Sunday...latest observation show light southwesterly winds
with seas in the 2 to 3 feet range. Forecast remains on track with
no changes. See previous discussion below:
Cold frontal passage...from north to south...will produce a shift
in winds from west to northwest through this afternoon. The slow progress of
the front south will allow winds to back a little bit over the
grand strand area in sea breeze close to the coast this afternoon. Can
expect only passing clouds associated with this front...but no pcp
expected with limited moisture present.
Northwest winds will dominate through this evening with a slight peak in
gustiness as front moves through...mainly remaining 10 to 15 knots in
the wake of the cold front. Winds will diminish tonight as weak
high pressure builds in with winds light north-northwest to start and then
backing around to the west-SW less than 10 kts as pressure gradient
relaxes overnight. With such light winds...there will be some
variability through tonight. Seas will slowly subside through
tonight to less than 3 feet with slightly higher seas off shore in a
mainly off shore flow. A light easterly swell with a period
around 10 seconds will drop off by morning.
Short term /Monday through Tuesday night/...
as of 3 PM Sunday...much of this period moderate SW marine winds
will prevail but below advisory levels. Wind-speeds may approach
exercise caution or advisory criteria into daybreak Wednesday
ahead of a frontal system. Warm air inland will produce a sea-
breeze or resultant wind that will back to S-south-southeast along the near
shore waters during the afternoon hours. No thunderstorms expected Monday
or Tuesday over the 0-20nm waters. Mariners are reminded sea
temperatures are 49-54 and insulated or thermal wear while offshore is
a good idea in case of unforeseen circumstances.
Long term /Wednesday through Friday/...
as of 3 PM Sunday...SW winds increase steadily during Wednesday
ahead of a cold front which will cross the area Wednesday night.
Wind speeds will become 20-30 kts...with gusts possibly exceeding
gale force. At this time it appears likely that a strong Small Craft
Advisory will be needed Wednesday and Wednesday night due to these
winds...and seas being driven up to 4-8 feet Wednesday evening. Cold front
crosses the waters overnight into Thursday morning...accompanied by
a rapid wind shift to the northwest...but with speeds remaining 20-25 kts
through Thursday morning. While these winds will remain
elevated...seas will gradually fall thanks to the offshore
component...becoming 3-6 feet Thursday morning...and falling steadily
through Thursday to 1-3 feet Thursday night on continued...but
weakening...northwest winds. Gradient relaxes considerably on Friday
allowing winds to slowly veer to the SW at speeds around 10
kts...with wave heights remaining 1-3 feet.