Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
1047 PM EDT Sat Aug 30 2014
Synopsis...deep high pressure will extend over the region through
the middle of next week.
Near term /through tonight/...
as of 1045 PM Saturday...
The latest surface analysis continued to show a slack gradient over
central North Carolina. Radar showed earlier showers had
diminished...as the sea breeze had moved north and weakened while
very dry middle-level air moved east across central and eastern North
Carolina on water vapor imagery. K indices should fall into the
teens as bufr soundings from the GFS and NAM along with rap
soundings show an overall stable air mass then.
Some of the temperatures across central North Carolina fell quickly
during mid-evening...but with some thin cirrus moving east from deep
convection well upstream...along with surface dew points around 70
to the lower 70s in most locations...temperatures are not expected
to continue that rapid fall. Lows should mostly be within a degree
or two of 70. Some low clouds remain possible late tonight
particularly as noted on NAM bufr soundings and the sref
probabilistic guidance...and alluded to more on the GFS 18z MOS
guidance output from its earlier...more optimistic 12z guidance. The
latest hrrr WRF would suggest a better potential for low clouds late
tonight in a narrow axis along and west of U.S. 1...where sref
probabilities are a little higher relative to the rest of the area
and closer to the higher 925mb winds. Those 925mb winds seem a
little high for fog in most places...to 20kt toward The Triad late
tonight...but the lower values of 10 to 15kt toward Interstate 95
along with expected dew points in the lower 70s could allow a little
more noticeable fog in patches toward there late.
Short term /Sunday and Sunday night/...
as of 230 PM Saturday...
A short wave trough over the MS River Valley to start the day will
lift to the northeast into the Ohio Valley through Sunday night.
However...its associated energy and deep moisture plume (emanating
from the gulf) will largely remain west and north of central NC. In
addition...the subtropical ridge centered over the southeast coast
should also help keep the better rain chances west of the area.
Therefore...will continue the forecast thinking of only isolated to
widely scattered showers/storms...with the best chances across the
west due to the proximity of the above features. Temperatures will continue
to be above normal...with highs generally in the lower 90s and
overnight lows around 70 degrees.
Long term /Monday through Saturday/...
as of 200 PM Saturday...
With roughly 3 weeks of Summer remaining (autumn equinox is sept
23)...the westward expansion of the subtropical ridge across much of
the southern Continental U.S....with the main belt of westerlies retreating
northward along the US-Canada border will result in the first
prolonged period of summertime heat and convective rain chances that
central NC has seen this season. Afternoon thicknesses are prognosticated
to run 25 to 30 meters above climatology...which should support
daytime highs ranging from 90 to 95f with lows in the upper 68 to
A low amplitude trough moving eastward across the northeast and Middle-
Atlantic States will temporarily flatten the upper anticyclone long
enough to allow a weak surface front to approach NC from the
north...but recent model trends over the last couple of days really
washes out the front to our north during the late Wednesday/Thursday
period. As such...gridded database will continue to exhibit
diurnally driven convection isolated to widely scattered storms each
afternoon...firing within a moderately unstable airmass along a Lee
side surface trough.
Aviation /00z Sunday through Thursday/...
as of 751 PM Saturday...
VFR conditions will continue through the evening. Low level moisture
remains high across the area with light surface winds... and IFR
conditions with stratus... and possibly some patchy fog.... are
expected to develop in the early morning hours Sunday at
krdu...krwi...and kfay... where dewpoints are highest. MVFR
conditions are possible at kgso and kint. Conditions will return to
VFR after 12z Sunday... with a few showers/thunderstorms possible in
Outlook...a summertime pattern will persist through early/middle next
week...with isolated to scattered afternoon/evening convection and a
potential for early morning fog/stratus.