Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
206 am EDT Wednesday Aug 20 2014
a cold front approaching from the north will stall over the area
through mid-week...bringing a period of unsettled afternoon and
evening weather. A building upper ridge will bring hot conditions
middle to late week...and heat advisories may be needed for portions
of the area on Thursday. A cold front and upper trough will drop
into the area by the weekend...bringing slightly cooler conditions
with a few showers and storms still in the mix through early next
Near term /until 6 am this morning/...
as of 10:30 PM Tuesday...significant convection has now passed well
offshore along with the associated middle-level disturbance. The odd
pop-up shower is still possible over the next few
hours...otherwise a dry overnight period is in store for the
Have updated forecast accordingly. Relevant portion of previous
In wake of the short-wave overnight...partial clearing should let
mins drop into the low/middle 70s inland and middle/upper 70s near
the coast. Beaches should hold around 80 into daybreak Wednesday.
Short term /6 am this morning through Thursday night/...
as of 300 PM Tuesday...the middle level flow will sharpen to more of a true
northwest flow for our area. This develops as the middle level ridge
builds across the Mississippi Valley. At the surface...an elongated
and skewed Piedmont trough will be the main feature. With this
flow...confidence is low in the timing and strength of shortwaves
and or mesoscale convective systems traversing the middle level flow.
The NAM in my opinion has actually been doing a better job with
these systems. For this package I will maintain the isolated
coverage for Wednesday with higher probability of precipitation for Thursday...especially
late when the NAM and GFS are in good agreement on a shortwave
Temperature guidance has actually cooled for daytime highs Wednesday
and I have shaved a couple of degrees off the forecast. Thursdays
values look essentially the same as the previous forecast. There is
a smattering of values that eclipse heat advisory criteria for
Wednesday but the longevity needed for an advisory will be marginal.
Thursday looks more like an advisory day with higher maximum
Long term /Friday through Tuesday/...
as of 300 PM Tuesday...ridge builds up the Mississippi Valley in the
middle to upper levels while a trough digs down into the middle Atlantic
through the period. Local area will remain in between the two
systems in a deep northwest flow. At the surface a cold front will
drop down from the north on Friday with high pressure ridging down
from New England into the Appalachians behind it. This will leave a
northerly surface flow over the area through the weekend. Low level
thicknesses and 850 temperatures will be on a downward trend as 500 mb heights
fall as trough digs down through the northeast. This will lead to a
general cooling trend with temperatures back down to normal by Saturday.
Temperatures may drop below normal as you factor in clouds and pcp produced
by impulses riding down in the northwest flow aloft. Overall will
experience more in the way of clouds and unsettled weather through
much of the period.
The deep northwest flow lightens considerably heading into next week while
the center of the surface high drops south from New England into the
Middle Atlantic States producing more of an on shore flow late Sunday
through Tuesday. Pattern shift will occur through Tuesday as surface
high shifts off shore with a southerly flow setting up. The middle to
upper trough will lift north at this time as ridge builds back into
the Carolinas. This should lead to a more Summer like pattern and
Aviation /06z Wednesday through Sunday/...
as of 06z...MVFR/IFR possible late overnight into the early morning
hours on Wednesday due to fog. Otherwise expect VFR with isolated
rain showers/thunderstorms and rain possible on Wednesday...mainly associated with the sea
Expect VFR/MVFR to prevail with calm or light northwest winds
early this morning. The exception will towards daybreak when
MVFR/IFR conditions possible and due to fog development mainly
inland and elsewhere where earlier rains occurred. An hour or 2
after daybreak...expect VFR throughout the day with light west-
northwest winds becoming south-southwest in the afternoon with
sustained winds at or below 10 kts. Could not rule out an isolated
rain showers/thunderstorms and rain ,mainly along the immediate coast...but with drier air
infiltrating in...do not anticipate the widespread coverage we
have seen over the past few days. Into the evening hours...winds
will become light and variable and skies will clear.
Extended outlook...chance afternoon/evening rain showers/thunderstorms and rain through the
period. Sub-VFR fog and/or ceilings will be possible during the
early morning hours each day.
near term /through tonight/...
as of 10:30 PM Tuesday...no changes to the forecast with the
latest update. Previous discussion follows:
Moderate SW winds to prevail through early Wednesday. Occasional
gusts to 2o knots can be expected through middle evening as the sea
breeze enhancement fades. Winds will tend to west late tonight as
a short-wave pulls offshore...possibly and briefly west-northwest-northwest early
Wednesday. Sea spectrum 3-4 feet significant wave
heights...composed off SW waves 3 feet every 5 seconds and southeast waves
1-1.5 feet every 9 seconds. Isolated to scattered thunderstorms should be
expected on the 0-20nm waters...mainly middle and late evening.
Short term /Wednesday through Thursday night/...
as of 300 PM Tuesday...light wind fields expected through the period
as an elongated and skewed Piedmont trough prevails across the
region. A brief west to northwest flow will be in place initially in
the wake of tonights shortwave. The direction will quickly turn to
southwest as the synoptic flow takes over. Basically wind speeds
will be ten knots or less with slightly higher values later Thursday.
Significant seas will be 1-3 feet through the period.
Long term /Friday through Sunday/...
as of 300 PM Tuesday...a cold front will drop south Friday into
early Saturday. Winds to the south of the front will be out of the west
to SW but will transition to a northerly flow behind the front as it
drops south late Friday into early Sat. Overall winds should remain
around 10 kts or less through the transition Friday into Saturday
but should see a bit of northerly surge late Sat behind the boundary
with winds increasing up to 15 kts. Lighter more variable winds will
maintain low end sea heights around 1 to 2 feet with afternoon chop in sea
breeze through Friday. Seas will build up to 2 to 3 feet in northerly
surge late Saturday.
By Sunday high pressure building down from the north will shift
winds to more of an on shore easterly flow around 10 kts. This will
help to push seas up around 3 feet through late Sunday into early