Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Wilmington NC
1026 PM EDT sun Oct 23 2016

high pressure over the southeast tonight will be pushed south by a
dry cold front Monday afternoon. High pressure building in from
Canada will bring cool conditions to the region for the middle of
the week. Temperatures will warm late in the week as the center of
the high moves offshore. Thursday night and Friday a weak cold
front slowly approaching from the west may bring a slight chance
of showers.


Near term /through Monday/...
as of 1030 PM Sunday...a few tweaks to temperatures based on 10 PM
observations. No significant changes were made, except for some
2-3 degree upward tweaks to low temperatures along the immediate
coast from central Horry County northward to Oak Island.
Discussion from 730 PM follows...

Surface high pressure centered along an axis from southern
Georgia to coastal Mississippi will actually retrograde a bit
overnight as low pressure dips southeastward through the Great
Lakes region. The surface pressure gradient will tighten up across
the mid- Atlantic states while remaining slack over the deep south
within the ridge.

With good radiational cooling and the boundary layer now
decoupling, greater changes are occurring just above the surface
where the tightening pressure gradient across the mid-Atlantic
will lead to increasing wind speeds across North Carolina and
points farther northward. Wind speeds at the 975 and 950 mb
levels (roughly 1000-2000 ft agl) should increase to 25 kt across
Lumberton, while remaining only 10 kt over Georgetown. This
should lead to a large difference in boundary layer turbulence
and the eventual depth of the nighttime radiational inversion.
I've therefore lowered forecast low temperatures by almost 10
degrees near the Santee river from Georgetown to south of
Kingstree, with lesser changes farther north.

Along the south-facing coast of Brunswick County, forecast lows
have actually been increased by a few degrees as the west-
southwest wind should advect in heat from the still-warm ocean
where sea surface temperatures remain in the 70s.


Short term /Monday night through Tuesday night/...
as of 300 PM Sunday...Monday afternoon temps shoot up to within a
few degrees of 80 in warm advection ahead of the next cool front.
This boundary moves through in the late afternoon and evening but
it will be running into this Bone-dry airmass so no precip. This
next high does not build in as aggressively as the chilly weekend
airmass did. Tuesday and Tuesday night will thus not be as cold or
breezy like Saturday was. Highs should hit the low 70s and lows in
the mid to upper 40s.


Long term /Wednesday through Sunday/...
as of 300 PM Sunday...surface high building in from the north Wed
shifts off the coast Thu as cold front approaches from the west.
Front is pushed east by shortwave crossing the Great Lakes Thu into
Fri. Aloft weak shortwave ridge overhead Wed flattens Thu as weak
troughing associated with the aforementioned Great Lakes shortwave
moves east. Moisture return ahead of the front is limited, as are
the dynamics and both the GFS and European model (ecmwf) solutions offer limited
precip chances. Best rainfall chances will be Thu night and Fri but
hard to imagine anything more than slight chc pop at this point.
Front is slow to exit the area, in part due to the weakness of the
5h trough, and the surface high building in behind the front lacks
cold air. Temperatures climb from a little below climo Wed to above
climo Thu due to development of return flow. Temps stay above climo
through the period, peaking ahead of the cold front on Fri.
Downslope flow helps keep temps above climo Sat/sun and, combined
with abundant sunshine, pushes highs into the low to mid 70s.


Aviation /00z Monday through Friday/...
as of 00z...high pressure centered to our southwest will continue to
dominate the weather with nearly clear skies. Winds will decouple
tonight, however little or no fog is expected. Due to the
orientation of the high pressure, expect westerly winds through most
of the forecast period, possibly becoming southerly along the coast
with the resultant by late afternoon.

Extended outlook...VFR.


near term /through tonight/...
as of 1030 PM Sunday...high pressure over the deep south will
actually retreat westward a little overnight as low pressure dives
southeastward across the Great Lakes. The approach of this low
should be enough to tighten the pressure gradient overnight,
particularly north of Cape Fear where wind speeds (currently
under 10 knots) should end up close to 20 knots late tonight! Seas
currently 1 to 2 feet should build by about a foot late tonight,
particularly over the North Carolina waters.

Short term /Monday through Tuesday night/...
as of 300 PM Sunday...prefrontal west-southwest winds to shift to northwest late
Monday afternoon and evening. There is no strong push of cool
air/high pressure behind this boundary, in contrast to the weekend
frontal passage. Conditions will not need any advisory or headlines. Further
veering to NE is then slated for Tuesday as the high progresses
eastward, while remaining well to our north.

Long term /Wednesday through Friday/...
as of 300 PM Sunday...weakening northeast flow on Wed veers to
southeast Thu as the surface ridge axis shifts offshore. Approach
of weak cold front Thu night and Fri leads to a period of south to
southwest flow but gradient remains weak with speeds staying
around 10 kt. Front pushes off the coast late in the period with
offshore flow setting up Fri night. Lack of cold advection/pinched
gradient will keep speeds under 10 kt. Seas 2 to 3 ft Wed drop to
around 2 ft Thu and Fri.


Ilm watches/warnings/advisories...



near term...tra
short term...mbb
long term...iii

National Weather Service Glossary of Abbreviations