Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1055 am EDT Wednesday Sep 17 2014
a Cool Ridge of high pressure will slowly build southwest across the
area through tonight...then intensify on Friday. This pattern is
expected to persist through the weekend...before a cold front
crosses the area early next week.
Near term /through tonight/...
as of 1030 am EDT...with the backdoor cold front now south of the
forecast area...abundant moisture on NE low level flow is filling in
the clouds across the region. Only slow/limited improvement in the
cloud cover is expected this afternoon...and isolated showers may
redevelop...as flow turns srly ahead of a shortwave moving through
the region. Temperatures are already on the cool side of guidance and this
will be maintained. Isolated probability of precipitation will be focused mainly on extreme
eastern/southeast sections...and along along the eastern mountain Escarpment through
late afternoon. Clouds should persist and/or redevelop in most areas
tonight...with min temperatures expected to cool to near climatology.
Short term /Thursday through Friday/...
as of 300 am Wednesday...Canadian high pressure will spread eastward into the
northestern states Thursday and Thursday night...extending southward enough to
reinforce the already cool air in place over the County warning forecast area. With upper
trough axis already east of the area...subsidence is implied and forecast
soundings from NAM/GFS indicate capping aloft though the GFS lapse
rates are favorable enough to think a few towering cumulus could go up. An
embedded shortwave will drift over the area early in the day albeit
without much moisture to work with. Will include a schc pop ahead of
the wave but expect afternoon convection to be inhibited.
A cad event will take shape by the end of the day Thursday as the surface high
shifts across the mountains Friday the upper flow weakens over the
area...with both NAM/GFS basically showing the trough filling over
the southeast. The parent high stays in motion as a result...moving
offshore but maintaining ridging down the eastern Seaboard. The
subsidence aloft being weaker...capping is less certain during
heating Friday afternoon. Allowed a schc pop to return to the forecast in the
most favored area...along the Blue Ridge where easterly upslope flow
will enhance development. US models bear their usual discrepancies
in terms of cape...but agree that shear will be very weak and
profiles quite dry through a deep layer. We/d probably be dealing
with pulse storms posing a damaging wind threat if cells were to
Long term /Friday night through Tuesday/...
as of 615 am Wednesday...no wholesale changes to the expectations for the
weekend and early next week. On Saturday the parent high associated
with the late-week cold air damming will be forced further offshore.
Easterly flow may continue in the low levels...but the influence of
The Wedge will be minimal. The pattern shifts and return flow begins
Sunday ahead of the next system affecting the eastern Continental U.S.. a weak area
of low pressure off the southeast coast is shown on both GFS/ec but
does not appear to have an impact this far inland. Probability of precipitation will remain
unmentionably low. Trough digs into the Ohio Valley and middle-Atlantic
Sunday night...accompanied by a cold front. GFS continues to be a
little faster than the ec in bringing the front into the area...and
the ec depiction of the trough continues to be stronger. Probability of precipitation Monday
appear to be a bit higher than climatology though neither model develops
significant quantitative precipitation forecast at this time. Both GFS/ec do show some instability
ahead of the frontal passage. Temperatures increase slightly each day through
Monday...with maxes around climatology that day. They then drop a couple
categories for Tuesday.
Aviation /15z Wednesday through Sunday/...
at kclt...the low cloud shield arising from NE flow moisture looks
fairly solid on satellite imagery this morning. Nearby Piedmont
sites are slowly lifting through IFR to lower end VFR...and that
should be the trend at kclt as well. Will adjust the timing to
exhibit a bit slower ceiling improvement than previously advertised.
Shower redevelopment may occur in the vicinity of the terminal this
afternoon...but the coverage should be quite isolated and confidence
remains too low to mention at present. Otherwise...steady NE flow
will become fairly light through the period. Low ceilings will likely
redevelop late tonight. Have maintained ceilings at the low end of the
MVFR category for now.
Elsewhere...MVFR ceilings are expected to persist at all the terminals
into the early afternoon hours. Ceilings should lift to VFR by middle afternoon..and
may even scatter out from time to time...especially at the upstate
SC terminals. Otherwise...light NE winds should generally persist
through the period. Low ceilings with possible Mountain Valley fog will
likely redevelop late tonight...and have maintained the flight category
at the low end of MVFR for now.
Outlook...the potential for late night/morning fog/stratus will
persist into late week...especially in the mountain valleys. Conditions
may finally dry out for the weekend. A cold front may bring
increasing chances for showers/thunderstorms early next week.
15-21z 21-03z 03-09z 09-15z
kclt high 89% high 92% medium 65% high 87%
kgsp high 89% high 100% high 100% high 91%
kavl high 89% high 93% high 86% high 95%
khky high 80% high 100% high 93% high 100%
kgmu high 89% high 98% high 100% high 95%
kand high 91% high 100% high 100% high 100%
The percentage reflects the number of guidance members agreeing
with the scheduled taf issuance flight rule category. Complete
hourly experimental aviation forecast consistency tables and ensemble
forecasts are available at the following link: (must be lower case)