Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
543 PM EDT Tuesday Sep 1 2015
Synopsis...a disturbance will drop southeast through the area
Wednesday night through early Thursday... but otherwise deep high
pressure will hold over the region through Friday... bringing hot
and humid conditions.
Near term /through tonight/...
as of 200 PM Tuesday...
A quiet evening and night ahead. Precipitable water values remain near or below
normal with dry air noted on water vapor imagery over the region.
Brief shortwave ridging holds over central NC ahead of the next
feature of interest... the potent vortex now over east-central
Indiana. At the surface... high pressure stretching across Tennessee/KY/WV
will hold in place tonight... with very weak and diffuse troughing
over eastern NC having little impact given the weak wind field. Will
maintain a mention of an isolated shower or two over the southeast County Warning Area into
early evening as the cumulus field is pronounced here... but expect very
little coverage considering the lack of any moisture/instability and
low shear without a convective focus. Skies should be mostly clear
to partly cloudy tonight... trending toward the latter late tonight
over the north and West County warning area where blowoff high clouds from
convection off the Texas/la coast may spread in... as suggested by the
experimental hrrr. Fog should not be as widespread or dense as this
morning but the eastern sections (where surface dewpoints will stay
elevated) could still see light fog late tonight with any dense fog
isolated in nature and confined to the climatologically-favored low-
lying areas over the NE County Warning Area. Lows in the upper 60s to around 70 with
generally calm winds. -Gih
Short term /Wednesday through Thursday/...
as of 230 PM Tuesday...
The low over east central Indiana is expected to open up and drop to
the southeast across our region late Wednesday into Wednesday night. The NAM depicts
1000-2000 j/kg of MUCAPE with deep layer shear rising to around 25
kts late Wednesday afternoon... not great but better than we're likely to
see at other times this week... although the NAM may be a tad too
high with afternoon dewpoints. With an overall weak wind field...
lack of high-level forcing features... barely-near-normal precipitable water... and
very little near-surface mass convergence... don't expect any
significant severe weather despite the DPVA accompanying the wave's
passage. Following the timing among the NAM/GFS/sref/ncar ensemble
output... will bring isolated storms into the far northwest County Warning Area after
18z... spreading into the rest of the Piedmont after 21z and
increasing to 20-30%... then progressing to the south and east
through the evening... before ending as mostly isolated showers over
the far southeast County Warning Area late Wednesday night. We should be in a relative subsident
area Post-wave on Thursday... with the weakening shear axis stretched
over the southern NC border area... so expect only isolated convection
coverage at most. Thicknesses will be well above normal...
suggesting highs around 90 to 95 both days... in line with
statistical guidance. Lows Wednesday night near 70 to the lower 70s. -Gih
Long term /Thursday night through Tuesday/...
as of 220 PM Tuesday...
A general weak upper level flow pattern will characterize the long
term with a couple of surface/low level features that will help
drive some of the sensible weather but in general a long term
forecast wrought with uncertainty.
After the surface wave moves through the area on Thursday there is
not a lot of factors supporting the wetter GFS solution over night
Thursday night into Friday morning. Prefer the Euro solution keeping
US dry overnight Thursday night but will carry slight chance probability of precipitation
because of the uncertainty.
Surface high pressure over New England will bring a back door cold
front through the area on Friday evening...providing some forcing
for better chances for showers and potentially a thunderstorm.
High pressure will continue to sink south later in the weekend and
precipitation chances will diminish over the area.
Temperatures will be warm to begin the period with highs in the low
90s and lows around 70 degrees. For the weekend...temperatures will drop to
the low to middle 80s for highs with lows in the middle 60s.
Aviation /00z Wednesday through Sunday/...
as of 545 PM Tuesday...
24-hour taf period: aside from a potential for MVFR/IFR visbys
associated with fog during the pre-dawn hours (08-12z) Wednesday
morning at the rdu/Fay/rwi terminals...VFR conditions and
light/variable winds will prevail through the taf period.
Looking ahead: a potential for isolated convection will be present at
all terminals as an upper level disturbance (centered near the in/Ohio
border at 21z this afternoon) tracks slowly southeast through the
virginias into portions of the Carolinas Wednesday night/Thursday morning...
though confidence is low with regard to whether or not convection
will even develop due to poor diurnal timing. A somewhat unsettled
pattern will result in a potential for convection the remainder of
the week into this weekend...particularly Friday into Sat. -Vincent