Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
634 PM EST Thursday Nov 26 2015
strong high pressure over the North Atlantic will control our
weather for the remainder of the week and into the weekend. A
cold front will approach from the west early next week and then
cross the area on Wednesday...bringing a chance for showers.
Near term /until 6 am Friday morning/...
as of 630 PM Thursday...quite a band of towering cumulus developed
in the relative heat/humidity of the afternoon across NE South
Carolina...dropping light showers between Florence and Kingstree
over the past 90 minutes. These showers have dissipated as surface
instability is approaching zero over land. Updates to the
forecast with this early evening update include slight tweaks to
min temperature forecasts based on latest guidance and anticipated
radiational cooling. Discussion from 300 PM follows...
Flow GOES from northeast in the low levels to northerly in the
middle levels. At the surface there continues to be a large and
strong area of high pressure affecting most of the eastern U.S.,
It's center off the New England coast. The northerly flow aloft is
related to a cutoff upper low sinking gradually southward into the
Bahamas. Usually such a deep flow off the Atlantic is quite
moisture laden but as visible satellite imagery shows this setup
is not. This is likely due to the upper low offshore, which has
shunted deep moisture well to our east. Not surprisingly models
have been far too aggressive with cloud cover for the past few
days. Other than a few SC in the 3.5-5kft layer the sky has
remained clear. Clouds offshore over the warmer SSTs have been
dissipating when hitting the cooler nearshore waters. Moisture
will come to bear in tonights forecast and the potential for fog.
Guidance differing considerably regarding fog potential not
dissimilar to last night. Favoring persistence and the moist model
bias as of late feel that fog potential is rather low. Have
relegated it to 'patchy' in the forecast for just a few hours
prior to daybreak as there may be just enough moisture trapped
beneath a surface-based inversion through 1.5kft.
Short term /6 am Friday morning through Saturday night/...
as of 300 PM Thursday...warm and dry weather expected to continue
into the weekend as ridging aloft and large high pressure at the
surface interact locally. High pressure extending from off the New
England coast will only slowly weaken through the period...in
conjunction with the aforementioned middle-level high doing the same.
Middle-level heights fall only slightly though...so this ridge is still
expected to block any precipitation from the trough and baroclinic boundary
extended across the Midwest. Large upper low retrograding to the
south well off the East Coast should have little impact locally.
All these features together suggest a dry period...but with moisture
slowly increasing in the form of cloud cover both in the middle
levels...and near the surface due to moist advection on NE flow
around the high pressure. Guidance has been pretty aggressive
bringing some of these showers onshore...but has also underestimated
the dryness beneath the ridging...so will maintain a dry forecast
with just slightly higher...but still silent...pop on the immediate
Temperatures will remain warm beneath the ridging...with widespread low 70s
across the area both days...slightly cooler along the immediate
coast where NE winds advect across cool shelf waters. Mins both
nights will also be above normal...middle to upper 40s Friday
night...around 50 Saturday night.
Long term /Sunday through Thursday/...
as of 300 PM Thursday...medium range guidance continues having
some trouble with the amplified pattern early next week and there
still remains some significant difference between the European model (ecmwf)/GFS
solutions. 00z European model (ecmwf) solution is in line with its previous
solutions and is in good agreement with the 12z Canadian and the
latest from wpc. The 12z GFS is a change from yesterday and
overall the GFS has been somewhat inconsistent during the last
several days. As such the forecast remains more in line with the
European model (ecmwf)/wpc solution.
The 500 mb low over the Great Basin this weekend will slowly start
making its way east. As that happens the baroclinic zone across the
plains and the MS valley drifts into the Kentucky/Tennessee Valley and the middle-
Atlantic region. Middle level ridging that had been over the region
will weaken sun and Monday while at the surface high pressure continues
to build down the coast. Better precipitation chances arrive on Tuesday as the
remains of the frontal zone and moisture associated with it move
into the region. Cold front associated with the system moving
through the Great Lakes midweek crosses the area Wednesday morning pushing
any lingering moisture/precipitation off the coast and is followed by
another round of high pressure.
Temperatures will be above climatology for much of the period. Cold
advection develops later Wednesday in the wake of the cold front and drops
temperatures below climatology for the end of the period.
Aviation /00z Friday through Tuesday/...
as of 00z...potential for areas of MVFR due to fog development late
overnight into the early morning hours. Otherwise expect VFR as high
pressure continues to dominate the current weather pattern.
VFR prevails this evening across the area with passing middle to high
clouds...few to scattered in nature. Intermittent gusts from earlier
have subsided...and will see northeast winds 5 to 10 kts continue
through the remainder of the valid taf period. Would not entirely
rule out patchy fog late overnight into early Friday
morning...mainly inland...though confidence is low at this time given the
lack of agreement in forecast models in the past few runs...along with
increased boundary layers winds...which may inhibit fog development
all together. After daybreak...VFR will prevail with nearly clear
Extended outlook...unsettled weather Saturday through Monday with a
chance of rain each day. Otherwise expect VFR.
near term /through tonight/...
as of 630 PM Thursday...only slight tweaks to the marine forecast
with this early evening update. Buoy/beach observed winds were
very close to forecast. I have tweaked wave height forecasts up
a bit based on 8-foot seas reported from The Frying Pan Shoals
buoy. We're watching showers closely. Models continue to indicate
these should dissipate before getting any closer than 15 miles
from Cape Fear. Discussion from 300 PM follows...
Although winds have dropped a bit below advisory levels seas have
not and will not. The high off the New England coast has
sufficient size and strength to channel advisory- worthy seas into
the area. With this high showing little movement through the
period conditions will be quite steady-state.
Short term /Friday through Saturday night/...
as of 300 PM Thursday...high pressure will continue to ridge down
the coast just inland from the coast this period...maintaining NE
flow across the waters. This setup will change only very little
through Saturday night...so NE winds of 10-15 kts will be common
both Friday and Saturday. These NE winds will have a prolonged
duration with a long fetch as well...so seas will remain 4-7 feet with
a NE wind chop predominant...then featuring a slowly elongating
period Saturday with deamplifying amplitudes to 3-5 feet by the end of
the period. Ongoing Small Craft Advisory has been extended into Saturday
evening...but expect all headlines to be lifted by Saturday night.
Long term /Sunday through Tuesday/...
as of 300 PM Thursday...northeast flow around 15 knots will continue
sun and Monday as high pressure ridges down the coast. Northeast flow
early Tuesday will become variable as the high northeast of the waters
retreats and flow eventually becomes southerly. By the end of the
period winds will be out of the south and on the low end of the 10
to 15 knots range. Seas 3 to 5 feet sun and Monday will diminish Tuesday as
speeds drop and direction becomes variable.
as of 300 PM Thursday...combination of prolonged NE winds around
high pressure and high astronomical tides as we move away from the
full moon...will likely create another morning of advisory level
coastal flooding Friday morning. The beaches will likely remain
below advisory thresholds...but minor coastal flooding is likely at
downtown Wilmington...and a renewed coastal Flood Advisory will be
needed tmrw morning.
Marine...Small Craft Advisory until 5 PM EST Saturday for amz250-252-