Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
637 am EST Thursday Dec 25 2014
sunshine will return this afternoon as dry high pressure southwest
of the area overspreads the southeast tonight into Friday. The high
will move offshore early Saturday. A cold front will drop into the
Carolinas on Sunday and may remain stalled over the area before
moving south by Tuesday...resulting in unsettled weather across the
Carolinas through middle week.
Near term /through tonight/...
as of 630 am Thursday...the surface cold front pushed offshore 1-2
hours ago. Behind this boundary a much cooler and drier airmass is
spreading eastward pushed by high pressure over the central Gulf
Coast. The upper level trough is approaching the Appalachians and is
becoming more positively tilted with time as the main vorticity
center accelerates NE into southern Quebec. Until this trough axis
reaches the area around noon a dense shield of cirrostratus and high
altostratus should continue to obscure the sky. These clouds will
unfortunately impact temperatures...shaving several degrees off what
would otherwise be a sunny and mild Christmas day. As it appears now
highs should reach 60 in most areas.
The high should move east into Georgia and the Carolinas tonight.
With generally clear skies expected the light pressure gradient
should allow winds to become calm with good radiational cooling
conditions. Lows should fall into the middle 30s away from the
beaches...following the cooler 00z NAM MOS guidance.
Short term /Friday through Saturday night/...
as of 330 am Thursday...high pressure sprawled across the
southeast will move off shore late Friday into Saturday. The ridge
extends from the low levels up through the atmosphere with plenty
of dry air and subsidence over the Carolinas. Pcp water values
will be down near a quarter of an inch through Friday but will begin
to rebound Friday night into Saturday reaching above an inch by Sat
evening as a deeper moister return flow sets up. Skies should remain
mainly cloud free through Friday into Saturday but will see some
clouds moving in from the SW by Sat evening. Overall expect plenty of
sunshine during the days with temperatures warming into the 60s as air
mass modifies. Temperatures will be warmer on Saturday after a slightly
warmer start to the day and increasing warm air advection. With the high nearly
overhead still on Friday night...decent radiational cooling will
bring temperatures down near 40 most places. By Sat night...dewpoint
temperatures will be up almost 20 degrees by Sat night. This combined
with increased cloud cover Sat night will keep low temperatures closer to
50. Have included low end probability of precipitation near daybreak Sunday as moisture
starts spreading north into the Carolinas ahead of an approaching
Long term /Sunday through Wednesday/...
as of 330 am Thursday...middle to upper ridge will get suppressed
farther south through middle week as a very broad trough rotates over
the northeast. This will produce an almost zonal flow with a
slightly SW to NE flow aloft. A cold front moving in from the west
on Sunday will get strung out in this almost zonal flow. Looks
like the cooler air may remain near or just to the north in
stalled boundary until it gets a push from middle to upper trough by
Tuesday. This will maintain warmer temperatures...clouds and intermittent pcp
Sunday through Tuesday as front remains stalled nearby and a few
waves of low pressure develop along it. Once front moves
south...temperatures should cool off a bit but warm air aloft will
overrun shallow cool air to produce low clouds through at least
middle week. Overall...a cloudy and damp long term forecast with
warmer temperatures to start and a cool down fro middle week...heading into
the New Year.
Aviation /12z Thursday through Monday/...
as of 12z...cold front has now pushed off the coast...with west
winds gusting to 20 kts or more. The upper trough still has to come
through...and until it does we will see a middle cloud ceiling for a
good portion of the day. High pressure will build in from the
southwest throughout the day...moving overhead tonight with light
winds. Have not put in any fog tonight at this time...but with all
the low level moisture...could not rule it out.
Extended outlook...VFR Thursday through Saturday. Rain returning
Sunday and possibly Monday.
near term /through tonight/...
as of 630 am Thursday...the cold front moved offshore within the
past 1-2 hours allowing 1024 mb high pressure along the Gulf Coast
to build eastward into the Carolinas. The gradient between this high
and strong low pressure over southern Canada will maintain a healthy
westerly wind the first half of today...with gradually diminishing
winds expected this afternoon and tonight. The Small Craft Advisory
will remain posted until 1800z/1 PM EST for all of our marine
forecast zones for both winds and seas...although conditions will
probably relax first along the SC coast where the advisory could be
lowered early if observations later support this.
The high will build east into the Carolinas and Georgia tonight with
winds veering northerly and diminishing further. Seas should subside
to only 2-3 feet.
Short term /Friday through Saturday night/...
as of 330 am Thursday...high pressure overhead on Friday will move
farther off shore through Saturday as a cold front approaches the
Carolinas. A light northerly flow early Friday will come around to
the south by Sat night but with high pressure remaining nearly
overhead as it shifts slowly east...winds will mainly be light and
variable...10 kts or less Friday and Sat. Overall seas will be 3 feet or
less but wna shows a very long period up to 17 second NE swell
mixing in over the weekend.
Long term /Sunday through Monday/...
as of 330 am Thursday...high pressure will shift farther off shore
as a cold front drops down from the north. This front may get hung
up over or just north of the local waters on Sunday with a southerly
return flow persisting Sunday into Monday before the front actually
gets pushed south by Tuesday. Uncertainty exists as to how far south
the front will make it and it may bisect our waters for part of the
time with northerly winds on the north side and southerly winds on
the south side. Winds may pick up slightly as front nears the
waters. Therefore seas may spike up a bit to near 4 feet late Sunday
into Monday but overall expect seas to remain 3 feet or less.
Marine...Small Craft Advisory until 1 PM EST this afternoon for