Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
647 PM EST Friday Dec 26 2014
dry high pressure will move overhead tonight before pushing
offshore on Saturday. Return flow behind the high will bring
increasing Atlantic moisture for the weekend with rain returning
by Sunday. Rain chances will persist into early next week. A cold
front moves through on Tuesday...followed by dry high pressure for
the beginning of the New Year.
Near term /through tonight/...
as of 6 PM Friday...mid/upper ridging with weak high pressure at the
surface will prevail through tonight. The column will remain mostly
dry tonight with some high cloudiness possible in the SW flow aloft.
as of 300 PM Friday...middle level ridge is expanding in size over the
Bahamas and Cuba. At the surface the center of the high is over the
Carolinas with a slight sense of expansion towards the north and
east through the period. Earlier there had been some cirrus level
moisture but even that is forecast to remain thin overnight.
Temperatures will thus readily radiate tonight...low temperatures ranging
from freezing over northwestern zones to around 40 for most of the SC coast.
A good night to catch a nice pass of the international space
station going from the northwestern sky at 631pm...passing right overhead
a few minutes later and then "setting" in the southeastern sky by
635 PM...all before it gets too chilly out. Even the moon will be
cooperative...its Crescent phase minimizing light pollution.
Short term /Saturday through Sunday night/...
as of 300 PM Friday...beautiful late-December weather to start the
weekend...but more unsettled weather will develop on Sunday.
Large upper ridge centered off the Southeast Florida coast will maintain
its presence on Saturday...with above normal thicknesses in place
into the Carolinas. Slow-moving surface high pressure beneath this
feature will drift offshore through Sunday...setting up warm/moist
return flow the second half of the period. Saturday still looks like
a very nice day locally with lots of sunshine and temperatures warming
towards 65 away from the beaches. Late Saturday cloud cover will
begin to overspread the region from the west...first in the form of
cirrus debris...and then lowering thanks to deep SW flow saturating
the column. At the same time...a weak shortwave will move just west
of the area...causing an increase in precipitation chances...and showers
are possible Saturday night...especially across the western half of
the County Warning Area. Theta-E ridge nudges towards the area Saturday night...but
it is weak...and total forcing is pretty weak...so quantitative precipitation forecast will be
minimal...and low-chance pop is all that is warranted. Mins Saturday
night will stay elevated due to clouds and warm surface
flow...dropping only into the upper 40s to around 50.
Sunday is an interesting day as precipitation may be ongoing first thing in
the morning...and then shut off for a time in the afternoon. The morning
precipitation will be residual rainfall associated with the aforementioned
shortwave and deep SW flow...but this will likely shut off in the
afternoon as subsidence promotes drying through a good portion of the
column. Late Sunday however...precipitation is expected to re-develop as a
cold front approaches from the west...driven by a dampening southern
stream vorticity impulse. Once again...the Theta-E ridge remains
weak...and jet-level diffluence stays displaces west of the
County Warning Area...but the best shot for precipitation appears to be Sunday night when
precipitable waters rise to 1.25 inches. Will bump pop to low-end likely in the
far northwest zones...and maintain inherited high-chance elsewhere. Temperatures on
Sunday will be quite warm after a warm morning low and continued
warm advection. Highs will rise to near 70 in the afternoon...with lows
Sunday night falling only into the middle/upper 50s.
Long term /Monday through Friday/...
as of 300 PM Friday...Monday starts out with a cold frontal boundary
draped over the Carolinas. Amazingly both extended models GFS and
European drop this front across the forecast area during Monday...to south and
east of the forecast area by Tuesday b4 stalling. Models do eye a weak
middle-level short wave trough that swings across the southeast states within west-southwest-east-northeast
flow aloft. The 2 models think that during this time frame a weak
surface low could develop from this short wave on the front prior to exiting
out over the Atlantic. Dynamics remain unimpressive with this upper
short wave trough...and no real tapping of Gulf of Mexico moisture just low
level Atlantic moisture. Thus will keep probability of precipitation on the low chance side
through Tuesday prior to the cold front sinking south of the forecast area.
Maximum/min temperatures prior to the cold front passage on Tuesday will run up to 10+ degrees
For Tuesday through Thursday...middle to upper level flow to remain split...with
Arctic flow coming out of central Canada across the Great Lakes to
the NE states. And for the ilm County Warning Area...middle to upper flow will mainly
be from the WSW-WNW. However...a 1050+ mb high will slide out of
Canada Monday to the Texas Gulf Coast by Wednesday. Low level flow will enable
some of this modified cold air to filter across the forecast area by Wednesday through
Thursday. Maximum/min temperatures for Wednesday and Thursday will actually be right at the
climatology norms. It will seem colder due to well above normal temperatures
leading up to the middle-week cold air. No probability of precipitation during this period.
Aviation /00z Saturday through Wednesday/...
as of 00z...nearly clear skies and light winds will prevail
through the valid taf period as high pressure remains across the
area. Given ideal radiational cooling conditions overnight...may
see patchy areas of fog development which could create periods of
MVFR. Otherwise...expect VFR.
Extended outlook...VFR through Saturday. Patches of light rain
returning Sunday and possibly Monday. VFR Tuesday.
near term /through tonight/...
as of 6 PM Friday...no changes to the current forecast.
as of 300 PM Friday...very quiet boating weather continues although
a warm coat advised along with life vests. High pressure very nearly
overhead to keep winds and seas at just about a bare minimum. A
light NE flow will be the dominant wind direction early on as the
high sits over land but its eastward overnight expansion should lead
to light and variable flow.
Short term /Saturday through Sunday night/...
as of 300 PM Friday...high pressure overhead to start the period
will migrate offshore Saturday...and then push further east during
Sunday. This all occurs while a cold front slowly approaches from
the west...so while the gradient will be weak most of the weekend...it
will begin to pinch late on Sunday. NE winds the first part of
Saturday will transition to be light and variable...before taking up
a SW direction Saturday night and all of Sunday. Speeds will be just
5-10 kts Saturday and Sunday...rising to 10 kts or a bit higher
Sunday night. Seas of 2-3 feet will be common through the period
regardless of wind direction...but will be choppiest late Sunday as
the winds increase.
Long term /Monday through Wednesday/...
as of 300 PM Friday...Monday to start out with SW-west flow at 10 to 15
knots ahead of the cold front. The front should drop from north to
south across the area waters late Monday night through Tuesday. Scec to
possibly Small Craft Advisory conditions to develop after its passage...with
northerly winds at 15 to possibly 25 knots through the remainder of Tuesday.
Significant seas will mainly be a combination of a 1-3 foot NE
ground swell at 11-13 second periods...and locally produced 2 to 4
feet wind waves at 4 to 6 second periods. Precipitation remains possibly ahead
and during the cold frontal passage.