Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
147 PM EDT Friday Aug 29 2014
Synopsis...a slow moving back door cold front will stall out across
central North Carolina today. The front will gradually dissipate
over the weekend as a light southerly return flow develops across
Near term /today and tonight/...
as of 1230 PM Friday...
As of 16z...latest observations/analysis indicates the surface front
has made it through 2/3rds the forecast area. Extensive cloud cover
is noted within the northeasterly flow along and north of the
front...with mostly clear skies across the extreme south. There
still is a great level of disagreement among the models with respect
to the evolution of this cloud cover...with the NAM keeping the
northern half of the forecast area mostly cloudy all day and the GFS
and rap breaking out the clouds some with more in the way of
easterly/southeasterly flow later today. However...the clouds are
hanging in and temperatures remained in the 70s across much of the northern
tier...more similar to the NAM. Sent out an update to reflect all of
this...with highs now expected to be in the low/middle 80s across the
north to the lower 90s across the extreme south. With regards to
precipitation chances...isolated to scattered convection is still expected
later this afternoon... especially in the vicinity of the
front...however recent models trends are showing very little in the
way of coverage. Overnight lows will generally range from the upper
60s across the north to the lower 70s further south.
Short term /Saturday and Saturday night/...
as of 220 am Friday...
Central NC will remain under the influence of an upper level ridge
Sat/Sat night as the center of the ridge currently over the
southeast states shifts slightly east toward the coast. The
lingering frontal zone over portions of central NC should wash out
during the day as a light S/southeast return flow develops across the
region. Forecast soundings suggest marginal destabilization with 500-
1500 j/kg of MLCAPE Sat afternoon. Given a prototypical summertime
'ridge' pattern...expect above normal temperatures...in the lower 90s.
Marginal instability and seasonable moisture (pwat values of 1.50-
1.75") would support isolated convection on Saturday...though forcing
for ascent will be limited to the seabreeze and differential
heating...primarily along the higher terrain in western NC...and it
is possible that no convection will develop in central NC. With the
above in mind...will indicate a slight chance of convection during
the after and early evening hours in the western Piedmont and southeast coastal
plain. Expect near normal lows Sat night in the upper 60s to lower
Long term /Sunday through Thursday/...
as of 245 am Friday...
A ridge will build over the southeastern states early to middle week.
This will extend our current more Summer-like pattern across NC well
into Wednesday. The core of the upper ridge is forecast to be over
the NC/SC coast Sunday. The approaching upper trough from the Ohio
Valley will be deflected to our north and weaken Sunday night and
Monday. Even with the heat and humidity with the southerly return
flow... only isolated afternoon thunderstorms are expected. The best
chance is forecast over and near the Blue Ridge where instability...
moisture... and lift will be highest. Highs should reach the 88-93
The core of the upper ridge is forecast to shift southwest with
time to over the Gulf Coast states Tue-Wed. This will allow a weak
Piedmont trough at the surface which may aid in the development of
scattered thunderstorms during the afternoon and evening early to middle
week. Otherwise... simply warm and humid with partly cloudy skies.
Lows 69-74. Highs 88-93 northwest to sandhills.
For middle to late week... any surface front is expected to be weak and
provide little if any cooling or drying. However... it may act as a
continued focus for scattered mainly afternoon thunderstorms Wednesday-
Aviation /18z Friday through Wednesday/...
as of 130 PM Friday...
A cold front has shifted south through the area throughout the day
today...with fairly extensive cloud cover along and north of the
boundary...with mostly clear skies south of the front (i.E. Extreme
southern portions of the forecast area...kfay). These MVFR ceilings have
persisted all day and will likely persist for at least the next
couple of hours. Some breaks this afternoon are still possible...
with a brief return to VFR conditions into the evening hours.
However...the moist air mass and light and variable winds overnight
should result in fog/low stratus development...with IFR/LIFR
conditions expected (especially towards the northeastern portions of
the forecast area...krwi...krdu). Conditions are expected to improve
to VFR by middle Saturday morning as the front gradually washes out
over the area. An isolated shower or storm will be possible later
this afternoon/evening and again Saturday afternoon...although
coverage will rather sparse.
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.