Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
1042 PM EDT Friday Oct 9 2015
a strong upper level system will bring moderate to occasionally
heavy rain Saturday with light rain lingering along the coast into
Sunday. The upcoming week looks dry with seasonable temperatures.
Near term /until 6 am Saturday morning/...
as of 1030 PM Friday...fair skies and mild temperatures continue
this evening. Radar composites and surface analysis show the next
anticipated cold front dropping southeast across the Appalachians. At a
rather rapid rate. Timing of precipitation still looks good though as
outlined in previous discussion. Latest update needed no
High pressure is dissipating just offshore as a cold
front...currently across the Ohio Valley...dives southeastward
toward the Carolinas. In the upper levels a positively tilted
trough will also dive southeast toward the Carolinas...with increasing
moisture advection and deep-layer ascent reaching the area late
tonight. Although there is currently a great deal of dry air above
the shallow cumulus at 4000 feet above ground level and cirrus aloft this layer
should moisten up quickly between 3-6 am with showers breaking out
before daybreak. Through 6 am the highest forecast probability of precipitation are 70
percent west of I-95 with probability of precipitation 30-40 percent along the coast.
There will be a period of limited radiational cooling this evening
before thicker high cloudiness arrives. This could drop temperatures
very close to forecast lows by 10 PM or so. Temperatures should then
rise a few degrees overnight due to stronger low-level winds and
clouds ahead of the actual front.
Short term /6 am Saturday morning through Sunday night/...
as of 3 PM Friday... the Carolinas are in an extremely rain sensitive
state right now due to the magnitude of the recent flood event.
Unfortunately another cold core upper low is forecast to cutoff
briefly to our west and channel deep layer moisture into the area.
However...this system will not benefit from having a tropical
connection as the one last week did and the rainfall rates will be
much, much lower. Overland flooding issues will likely be in the
minor category, often addressed with flood advisories instead of
warnings. Impacts to river flooding are expected but unless we are
surprised with more rainfall than forecast they should be relatively
minor and tend to be limited to slowing rate at which The Levels
fall most notably perhaps on the Black River. By Saturday night the
cutoff will be opening up and traversing the coast line. At this
point the deep moisture feed cuts off as does the heavy rain. Light
rain wrapping around the system could persist into Sunday however
mainly along the coast.
Long term /Monday through Friday/...
as of 3 PM Friday...the middle level pattern will generally consist
of troughing across the eastern U.S. With an indication of a Rex
block out west. The troughing across the east will be enhanced
Tuesday/ Wednesday and again late in the period with embedded
shortwaves. Both of these features will push cold fronts through
the area. The first front pushes across late Tuesday with the
latter front crossing the area Friday. Both will be moisture
challenged and we continue to advertise a dry forecast through the
period. The latest mex guidance shows temperature trends mostly
stable with some air mass modification Wednesday and Thursday.
Just beyond the valid time period of this package the mex is
showing widespread 40s Saturday morning.
Aviation /03z Saturday through Wednesday/...
as of 00z...VFR conditions to prevail across all terminals this
evening. Bubble surface high to push off the Carolina coasts and
offshore this evening. Cold front dropping southeast will reach
the I-95 corridor during the pre-dawn Sat hours...and off the
Carolina coasts during the daylight hours of Sat morning before
finally and temporarily stalling just offshore. After The
Cup...thats when the surface pg tightens resulting in northwest to NE winds
around 10 knots. Light stratiform precipitation will occur after The Cup...and
become steadier and heavier later Sat morning and afternoon. This
in response to a potent middle-level short wave trough that dives southeast and
closes off nearly overhead by late Sat. Dynamics aloft may
overcome the weak instability at the surface...and aid the possibility
for convection to affect the forecast area and local terminals. Basically
looking at MVFR with possible IFR from low clouds and reduced visibility
this morning...and IFR this afternoon from low clouds and possible
Extended outlook...IFR/MVFR ceilings and lingering light rain to
remain present into Sunday morning. Improving conditions during
the day Sunday. VFR Monday with a chance for showers on Tuesday.
near term /through tonight/...
as of 1030 PM Friday...latest observation show benign conditions continue
over the waters this evening...wive elements S to SW winds of
around 10 kts and 2 feet seas. No changes needed with the evening
update...previous discussion from this afternoon follows:
High pressure just off the coast is dissipating as a cold front
across the Ohio Valley moves southeastward. This front should wait
until after daybreak to cross the coastal waters with generally
southwest winds expected until then. Seas around 2 feet consist
mainly of two small swell sets (e and se) however there also will
be a small short-period chop developing due to the southwest
Short term /Saturday through Sunday night/...
as of 3 PM Friday... an upper low Vermont elements approaching from
the west early Saturday will have a surface reflection along the
SC/Georgia border. This normally puts the area in a fairly robust S or
southwesterly flow. However with surface high pressure also nosing in from
points north the wind direction may be a little hard to ascertain
in a poorly defined pressure pattern. By afternoon however the low
cuts to our south and the high pushes in turning the winds to a
more pronounced northeasterly direction. Of note this is not a
strong surge of high pressure. The coast-parallel NE flow
continues into Sunday with similar speeds. The steady-state flow
will allow for some building of seas along the 20nm border and
some 4 feet waves may be introduced to northern zones.
Long term/Monday through Wednesday/...
as of 3 PM Friday...Monday will generally be a transition day
from light and variable winds as weak low pressure moves off to
the northeast and a southwest flow develops later as a front
approaches from the west. Winds will be mostly northerly early
Monday and shift to east/southeast with the sea breeze. By Monday
evening wind speeds increase to 10-15 knots from the southwest.
Speeds increase further Tuesday to 15-20 knots before the front
moves across late Tuesday with a modest northerly flow ensuing.
Significant seas are mostly 2- 4 feet with the higher values
associated with the higher wind speeds Tuesday.
as of 1030 PM Friday...tide gage at downtown Wilmington now
indicates that minor coastal flooding has ended for the night. In
progress. This is as expected and the coastal Flood Advisory has
expired on time at 10 PM. Previous discussion from this afternoon
Tidal anomalies at the ocean and ve elements along the Cape Fear
River have shown a distinct downward trend over the past two days.
Extrapolating this trend forward for the Cape Fear River at
downtown Wilmington gives a water level anomaly of barely +1.0
feet at the time of high tide this evening. This should produce
very minor tidal flooding at high tide this evening with impacts
limited to the west side of the river near The Battleship