Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
1032 am EDT Tuesday Jun 30 2015
Bermuda high pressure will become re-established across the area
today and will persist through the remainder of the week and into
the upcoming Holiday weekend. This will create slightly above
normal temperatures...along with typical summertime thunderstorm
chances each afternoon and evening.
Near term /through tonight/...
as of 1030 am Tuesday...although current dewpoints across the
area are well into the 60s...near 70 in some places...these values
should start dropping. Forecast and observed 12z soundings from
chs/mhx show an abundance of dry air just above the surface to
about 850 mb. Once deeper mixing develops this dryer air will work
its way to the surface...dropping dewpoints into the upper 50s
inland and middle 60d along the coast. The dry air is likely to be
enough to stave off any deep convection through at least the middle
afternoon hours. Later this afternoon and evening increasing positive vorticity advection
ahead of a shortwave rounding base of the 500 mb trough...centered
over the Kentucky/Tennessee valleys...and an influx of higher dewpoint air will
help kick off storms. A broken line is expected to develop
southwest of the forecast area during the afternoon hours and then
lift northeast...crossing the area late this afternoon into early
evening. Not sure if this activity will ultimately reach the NC
coast. The best positive vorticity advection slides off to the northwest and by the time
the line reaches coastal NC diurnal instability will be waning.
Did make a few adjustments to the previous forecast...mainly to
include higher pop for inland areas. Although dewpoints will be
lowest here this is where the strongest positive vorticity advection associated with the
approaching shortwave will be found. This area is also likely to
be the hottest and where late day dewpoint recovery will be
greatest. Storm Prediction Center has maintained the slight risk for severe weather
across western Darlington and Marlboro counties while the bulk of
the remaining forecast areas remains in marginal risk. Sounds do
suggest the possibility of downbursts...be it a small chance...so
will go ahead and mention severe potential in severe weather potential statement.
Short term /Wednesday through Thursday night/...
as of 300 am Tuesday...broad trough across the east will keep its
ridge axis west of the area through the period. This drives temperatures to
above climatology...but will maintain scattered convection each afternoon/evening
in typical diurnal fashion. Weak shortwaves may move overhead at any
time during the period which could enhance convection...especially
across western zones which will be closer to the trough axis and the
forcing associated with any vorticity maximums. Convection will be
primarily diurnally forced...and the GFS showing widespread showers
along the coast Wednesday appears to be overdone. For this reason
will cut back inherited pop a bit Wednesday and just maintain low
chance by day - schc/silent at night. Temperatures will average 3-5 degrees
above climatology for highs and lows...with widespread low 90s during the
aftns...and middle 70s overnight.
Long term /Friday through Monday/...
as of 300 am Tuesday...Bermuda ridge will persist through the
extended in usual July fashion...with the only significant changing
feature being the deamplification of the middle-level flow. Trough
across the east will flatten into the weekend...with slight ridging
developing by early next week. This will lead to a warming
trend...as well as decreasing pop each day. The GFS is showing a
stationary boundary hovering across NC during the weekend...but this is
not agreed upon by other guidance or wpc...nor is it supported by
the middle level pattern. For this reason will hedge against the GFS
solution and show slight warming each day from just above climatology to
several degrees above climatology for both maximum and min...with decreasing
convection chances each day. However...as noted by the previous
forecaster...very difficult to keep a dry forecast this time of
year...so will show at least schc pop each afternoon for the sea breeze
and Piedmont trough convection.
Aviation /15z Tuesday through Saturday/...
as of 12z...terminals will be VFR this morning with light SW-west
winds. By late morning and early afternoon winds will become SW
10-15 kts...except S-south-southwest at 15-20 kts at the coastal terminals.
VFR will continue during the afternoon with with scattered skies
consisting of low level cumulus and high level cirrus. There is a
chance that vcsh could develop mainly SC terminals middle-late afternoon
but confidence is low. But forecasts are in general agreement that
showers and thunderstorms will move across the terminals this
evening as a short wave moves through. Confidence of coverage is
low however due to moisture availability. Will indicate vcsh/thunderstorms in the vicinity
for now and update in later tafs. Winds speeds will decrease later
in the evening and early morning hours to SW 4-8 knots.
Extended outlook...predominately VFR with decreasing chances of
showers and thunderstorms each day through Saturday.
near term /through tonight/...
as of 1030 am Tuesday...west-southwest flow in the 10 to 15 knots
range will become more southerly and increase in speed this
afternoon. Development of sea breeze and strengthening of Piedmont
trough will tighten up the gradient over the waters. Southerly
flow will increase to almost 20 knots with potential for higher
gusts. Seas in the 3 to 4 feet range for much of the period may
briefly peak at 5 feet in the afternoon and evening near the 20 nm
Short term /Wednesday through Thursday night/...
as of 300 am Tuesday...typical summertime pattern through the
period with Bermuda high pressure offshore and a Piedmont trough
lying inland from the coast. This will drive SW winds across the
waters through the period at 10-15 kts...with enhancements each
evening to 20 kts as the Piedmont trough sharpens. Blend of
inherited wave heights with the latest nwps run brings seas to
just below 6 feet each evening as the winds increase...but it is
possible that advisory conditions will develop...especially
Thursday aftn/eve. Have kept current forecast at 3-5 feet through
the period...and a scec is probably Thursday...with the Small Craft Advisory a
Long term /Friday through Saturday/...
as of 300 am Tuesday...entering the time of year when the Bermuda
high becomes a semi-permanent feature...and this will be the case
during the extended. This means little variation in marine
conditions each day...with SW winds around 15 kts pretty much
constant. These winds will combine with a southeast swell to push wave
heights to 3-5 feet...slightly higher at times in the evening as the
gradient gets pinched in the Lee of the sharpening Piedmont