Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
235 PM EDT Thursday Jul 31 2014
cool high pressure will linger over the area today. The remains
of a stationary front will lift north as a coastal trough on
Friday then stall over the area during the weekend. This will
bring good rain chances...with periods of heavy rainfall
possible...Friday through Monday. More seasonable weather will
develop the middle of next week.
Near term /through tonight/...
as of 130 PM Thursday...latest radar imagery depicts a few showers
beginning to pop up across portions of our area...with coverage
increasing south and west of our area as well. Expect this gradual
trend of isolated to scattered showers across our area to continue
through the rest of today and through the overnight hours as
isentropic lift increases across the area with precipitable water
values around 1.6 to 1.7 inches. Would not entirely rule out an
isolated thunderstorm...however...mid-levels remain fairly dry thus
widespread coverage of any convection has a low probability. In
addition...we will see the continuation of increasing cloud cover
this afternoon with temperatures in the low to middle 80s as surface high
remains in place through tonight. Given cloud cover already in
place...with the exception of an added degree here or there over the
next few hours...overall are close to...if not at already...our
highs for today.
As a few weak disturbances continue to propagate around the
unseasonably digging longwave trough in place across the eastern
half of the US today...a synoptic transition will continue to take
its course well into the overnight hours. Focus turns to the surface
frontal boundary stalled offshore...which will retrograde back
towards the Carolina coast as a warm front by morning. While
time-height analysis continues to depict fairly dry
mid-levels...available moisture in the upper levels supports
previous thinking that cirrus cloud deck will increase and persist
through the period. Given anticipated cloud cover...have slightly
tweaked overnight lows...but continuing overall with around 70
Short term /Friday through Saturday night/...
as of 230 PM Thursday...period continues to look unsettled with
increasing deep moisture and developing low level convergence. Middle
level trough hanging over the eastern Continental U.S. The past several days
starts to weaken and shift west as 500 mb ridge over the western
Atlantic expands. Meanwhile at the surface western Atlantic high
will extend west...pushing front stalled off the coast into the
region. Deep southwest flow...tapping Gulf moisture...combined
with low level southeast flow...tapping Atlantic moisture...will
push precipitable water values to and above 2 inches for much of
the period. Divergent flow aloft and low level convergence along
the quasi-stationary boundary in a moderately unstable environment
should produce plenty of showers and thunderstorms. Not
anticipating any widespread strong to severe storms but given the
time of year cannot rule out an isolated stronger storm. Although
there is likely to be a diurnal increase in activity precipitation
chances will remain elevated overnight given favorable conditions.
High temperatures will continue to run below climatology with cloud cover
and precipitation keeping highs in the low to middle 80s. Southerly
flow...increasing moisture...and cloud cover will keep lows near to
slightly above climatology...low to middle 70s.
Long term /Sunday through Thursday/...
as of 230 PM Thursday...atypically well defined (for the time of
year) middle and upper level troughiness to our west on Sunday.
Decaying surface boundary to provide low level lift...which will
then be aided by middle level positive vorticity advection and upper divergence associated with
right entrance of upper jet streak across northeast and middle
Atlantic. And while rain chances seem to warrant likely probability of precipitation
models are not suggestive of high quantitative precipitation forecast amounts. This may be due to
it being such a cloudy day that very little instability manages to
develop save for perhaps along the immediate coast. These players
all remain nearly in place heading into Monday although all of
them weaken. Looking for another day of high probability of precipitation and suppressed
afternoon temperatures. Tuesday should bring lower rain chances but still
ones that are higher than normal. The upper jet continues to
weaken and lift out to the northeast while the middle level trough
weakens...but also sends its remaining vorticity center across the
Carolinas. In response to this the GFS straightens the Piedmont
trough at the surface. We also may see a bit more sunshine in
contrast to the early parts of the period. Tuesday may thus be a
day where we transition to more scattered and deeper convection
especially if temperatures start bouncing back towards climatology. Wednesday and
Thursday look seasonable with respect to both temperatures and
areal coverage of convection. Middle level flow should be of a drier
westerly direction while some semblance of a Piedmont trough
Aviation /18z Thursday through Tuesday/...
as of 18z...VFR conditions for the rest of today may deteriorate to
MVFR overnight as rain chances increase across our area. Will
maintain broken ceilings this afternoon as cloud cover associated with the upper
trough continues to stream overhead. East winds have picked up more
than expected...so have added prevailing winds around 10 kts with
higher gusts at the coastal terms. Rain chances inland increase this
evening as weak upper disturbances rotate around the trough...so
will maintain vcsh for kflo/klbt after 00z Friday. As the stalled front
offshore lifts back northward as a warm front overnight...showers
may encroach upon the coastal sites after 06z Friday. By 12z the front
should be draped over our County Warning Area with -shra at all taf sites. Winds
will shift to the southeast behind the front. Depending on how
persistent and how early the rainfall begins...MVFR ceilings could
develop overnight or hold off until early Friday morning. Though brief
IFR ceilings cannot be ruled out...MVFR should prevail based on the
Extended outlook...shra/tsra likely with periods of MVFR conditions
Sat through Monday as a front stalls and finally dissipates over the
eastern Carolinas. Chance of showers continues on Tuesday.
near term /through tonight/...
as of 130 PM...with weak surface high pressure across land and a warm
front offshore moving closer to the waters through the
period...expect east winds to persist across the waters through
the period...with sustained winds around 10 to 15 kts and gusts
near 20 kts possible. Seas will be 3 to 4 feet.
Short term /Friday through Saturday night/...
as of 230 PM Thursday...period will be dominated by southeast
flow as front stalled offshore moves to the coast Friday then pushes
onshore Sat. Gradient will be weak for much of the period with the
only possible exception during Friday night when gradient sharpens as
boundary becomes a little more defined. Speeds Friday night may touch
15 knots but otherwise speeds will be on the lower end of the 10 to
15 knots range. Seas 2 to 3 feet early in the period increase to a
solid 3 feet given the prolonged southeast winds and development of
east-southeast wind wave.
Long term /Sunday through Tuesday/...
as of 230 PM Thursday...light southerly winds on Sunday with
frontal boundary just inland of the coast. Wind chop will be
coincident with 11 second southeasterly swell. The weakening
boundary will move further inland for the remainder of the period
and the west Atlantic high pokes a bit westward further into the
Carolinas. This could lead to an occasional increase in flow by a
few knots and also a slight veer from S to SW.