Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
310 PM EDT Tuesday Jul 29 2014
Synopsis...Canadian high pressure will extend into the Carolinas
and middle Atlantic through mid-week. Moisture will be on the
increase Thursday and Friday as a coastal front spreads inland.
Near term /through Wednesday night/...
as of 230 PM Tuesday...
Scattered to broken stratocumulus is now extending into the western
areas of the County Warning Area. This may keep maximum temperatures from breaking
80 degrees in the western Piedmont and extreme southwest. Otherwise
temperature forecast appears to be on track with highs in the upper
low to middle 80s north to south. Overnight will be dry with lows in
the upper 50s to lower 60s. While model guidance appears to hint at
some MVFR visibilities near daybreak in the east...forecast
soundings appear too dry in the low levels for this to happen.
Potential cloud cover overnight would also help to lessen any fog
Wednesday will have continued subsidence keeping dry conditions in
place with a slight warming trend but still in the low to middle 80s
for highs with upper 50s to low 60s once again for minimum
temperatures. Scattered to broken cloud cover in the 5-8 kft range
will have the heaviest concentration in eastern areas of the County Warning Area
which may help keep maximum temperatures down a degree or two from forecasted
Short term /Thursday through Thursday night/...
as of 310 PM Tuesday...
Deep upper troughing over the eastern half of the US will continue
Thursday...though with a brief relaxation and height rises aloft
between a shortwave lifting off to the northeast and energy diving
through the plains states. Thicknesses rise about 10m over
Wednesday...starting out at 1395m Thursday morning...which should
yield 83-87 under mainly partly cloudy skies. Dewpoints still in
the 50s and lower 60s will limit cape to a couple hundred j/kg or
less...though a little better moisture at the top of the boundary
layer may help enhance cloud cover across the southern portions of
the area...especially along the seabreeze. Any showers and storms
should remain south of the area. Clouds...especially middle and high
clouds will continue to increase Thursday night as a shortwave dives
through the deep south. Lows will be mostly in the middle 60s.
Long term /Friday through Tuesday/...
as of 310 PM Tuesday...
The Friday through Tuesday period is one of mixed confidence.
Models are in good agreement that the mean upper trough axis will
remain west of the Appalachians...placing NC in southwesterly flow
aloft and in the right entrance region of an upper jet along The
Spine of the mountains. An inverted coastal trough will slowly
meander westward over the weekend and then likely wash out by early
next week as the trough weakens and the western Atlantic ridge
builds westward. This will cause precipitable water to continue to increase to
upwards of two inches by Sunday. While this points toward a wet
weekend...confidence is low when it comes to best time frame for
precipitation. On Friday...models are showing a disturbance emanating from
convection over the High Plains that sweeps around the base of the
trough and then lifts across our region. Its hard to put much Faith
in such a feature three days out...but all models have shown an
increase in quantitative precipitation forecast for Friday...so have increased probability of precipitation into the 40-50
range. However...beyond Friday there is very little to key on for
forcing other than the aforementioned jet and weakening coastal
trough. Thus...will have chance probability of precipitation in each day be keep them below
50 percent until it becomes more apparent which day will be favored.
Thunder potential looks limited Friday and Saturday given limited
instability with weak lapse rates aloft and relatively cool daytime
temperatures in the upper 70s and lower 80s. A warming trend should endue
by Sunday and Monday as the upper ridge and Bermuda high strengthen
to our east.
Aviation /18z Tuesday through Sunday/...
as of 110 PM Tuesday...
24 hour taf period: moderate to high confidence of VFR conditions
through the end of the taf period. The only caveat to that is model
guidance showing some small chance for some MVFR visibilities in the
east closer to sunrise. A look at the forecast soundings does not
make this seem likely and so will leave it out of the tafs for now
but this is a possibility between 9z and 12z at krdu...kfay...and
krwi. Otherwise light and variable winds with a predominantly north
or northeasterly direction should prevail through the taf period.
There is a chance that some southwesterly winds will begin in the
south and east at the very end of the taf period.
Long term: a front that has stalled offshore may retrograde back
over eastern NC by the end of the week...potentially resulting in
periods of sub-VFR conditions.