Area forecast discussion
National Weather Service Wilmington NC
929 am EDT Friday may 24 2013
Synopsis...
a cold front will bring cooler and drier air into the region today
and through the weekend. A gradual warmup will begin on Monday with
seasonable temperatures expected for much of the next coming week.
No significant rainfall chances are expected in the extended period.
&&
Near term /through tonight/...
as of 9:30 am Friday...analysis of morning soundings and a look at
the latest guidance confirms earlier hypothesis that we could see
some showers pop up early this afternoon as the unseasonably deep
upper trough swings overhead and lapse rates steepen. Dewpoints
still in the 60s most places so there is enough low level moisture
to generate a cumulus field as the day warms up. Relevant portion of
previous discussion follows:
East-bound cold front has cleared the coast at 10z. Upstream
dewpoints are beginning to fall. Mosaic radar loops show a few
showers over the mountains this morning beneath the cold pool
associated with an approaching upper trough. These may arrive over
our forecast area by afternoon despite dropping dewpoints...and
will retain isolated showers between 17z-20z in peak heating.
Time-height plots of relative humidity do show there may be enough residual low-
level moisture across the eastern half of our forecast zones to
set-off a few showers between 1pm and 4pm.
Daytime cool air advection with minimum temperatures starting off
between 65-70 degrees will bring a low diurnal temperature range
today...with readings expected to climb 15 degrees f or less from
sunrise to middle afternoon. With this in mind have shaped maximum
temperatures in the upper 70s across our northern zones and 80-83 along
our coasts and southern zones where the down-slope component is
slightly greater. Drying and clearing tonight is expected and
minimum temperatures by daybreak may approach record low values.
Record lows for may 25th are ilm-50 lbt-45 flow-48 myr-52 and
cre-55.
&&
Short term /Saturday through Sunday night/...
as of 3 am Friday...after an unseasonably chilly start Saturday will
turn out pleasant with full sunshine and fairly light winds. These
winds will still be out of the north to northwest however keeping daytime highs
over a category below climatology thanks to cutoff upper low/occluded
cyclone near Nantucket. As the cold air advection shuts off to neutral and a small
increase in cloud cover occurs Sat night temperatures will dip down
to within a few degrees of 50...not quite as cool as the previous
night. Very weak warm air advection on Sunday to add a few degrees to highs as well
as generate a little cloud cover but still looking at about 5 degree
shy of seasonable temperatures. A continuation of below normal temperatures
rounds out the period with lows in the low to middle 50s Sunday night.
&&
Long term /Monday through Thursday/...
as of 3 am Friday...return flow sets up to start next week albeit
somewhat weakly on Monday and highs may still end up a few degree below
climatology. Increasing dewpoints will be noticeable too in the onshore
flow. Tuesday into Wednesday will bring a significant building of
the upper ridge across the eastern U.S. While high pressure sprawls
across the western Atlantic. The amplitude of the upper ridge
certainly argues for unseasonable warmth but the ridge axis just north
of the region will keep a deep easterly flow into the Carolinas.
That is...the southerly component will be minimized much of the
time. The cooler shelf waters should thus have a moderating effect
on the warmth...most pronounced near the coast. The capping effect
of the the ridge paired with the stabilizing effects of the surface
marine air will keep meaningful rain chances out of the forecast.
&&
Aviation /13z Friday through Tuesday/...
as of 12z...front has now exited the coast with northwest flow at
all terminals. High confidence for VFR conditions through the
forecast period. Winds may hold off the gustiness until midday...as
that is when the cold air advection begins in ernest. A clear and
crisp night in store with an unseasonably cool airmass dropping in.
Extended outlook...morning fog possible Monday and Tuesday.
Otherwise VFR.
&&
Marine...
near term /through tonight/...
as of 9:30 am Friday...keeping Small Craft Advisory in place for
this afternoon and evening for gusts to around 25 kts. Winds still
at sub-advisory levels now but should pick up now that the cold
front has moved across the waters. Latest observation show northwest winds at
around 10 kts with 3 to 4 feet seas. Previous discussion follows:
Small Craft Advisory flags hoisted for all of our southeast NC and NE SC
waters from 3pm-9pm today...to address 25 knots northwest wind gusts
anticipated later today into tonight. Seas generally will hold 3-4
feet most waters but up to 5-6 feet along outer portion subjected to
longer fetch build-up. Thunderstorms may also be expected but mainly
confined along the west wall of the Gulf Stream current today and
tonight. Peak winds north-northwest 15-25 knots are expected between 5 PM- 8pm as
the departing front and encroaching high pressure have the
greatest surface pressure gradient interaction. Seas will take on a
bumpy character today as residual southeast wave energy born from
offshore Bermuda high pressure contends with increasing wind-waves
opposing from the northwest.
Short term /Saturday through Sunday night/...
as of 3 am Friday...pleasant boating conditions expected through the
period. High pressure building in gradually from the north to keep a north
to northwest wind through the period that will be capped at 10kt due to a
fairly weak gradient. The storm helping to drive the high will be
all the way up near Nantucket on Saturday and only gradually lifting
into Nova Scotia Canada into Sunday. Some backswell from this system
will be intercepted by Cape Hatteras and not much should make it
this far south due to wave shadowing. Thus expect fairly small seas
to the tune of 2 feet or less through the period...with the smallest
waves off of Brunswick County where offshore flow component is maxed.
Long term /Monday through Tuesday/...
as of 3 am Friday...weak return flow sets up on Monday as high
pressure finally establishes center off the coast. Its proximity to
the landmass will keep wind speeds at 10 knots or less and in the
absence of swell energy the diminutive wind wave of 2 feet or less
will be the predominant wave. The west Atlantic high becomes larger
into Tuesday making its center farther way but leading to little
change in local wind flow. Deep and long fetch easterly swell will
be getting established into the Bahamas and this will likely start
to generate some swell energy into the Carolinas but not until after
the period.
&&
Ilm watches/warnings/advisories...
SC...none.
NC...none.
Marine...Small Craft Advisory from 3 PM this afternoon to 9 PM EDT this
evening for amz250-252-254-256.
&&
$$
Synopsis...mbb
near term...mjc/rek
short term...mbb
long term...mbb
aviation...mjc/dl
marine...mjc/rek/mbb
