Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
320 am EDT Friday Sep 4 2015
a cold front is expected to push south across the region today.
This will be followed cool and moist high pressure which will
persist through through the Holiday weekend. A gradual warming trend
will follow toward the middle of the week.
Near term /through tonight/...
as of 255 am...a weak short wave and area of upper divergence drop
into the area through the period. At the surface...a weak boundary moves
across the area today. High pressure builds in from the NE
reinforcing the northeasterly flow across the area. Copious low level
moisture remains over the area. This combined with the expected
heating will lead to moderate instability. Expect convection will
develop again today...but will have a little later start time.
Convection begins near the Blue Ridge and spreads east and south
through the day and into the early evening. Best coverage will be
across NC with likely pop for the I-40 corridor. There will be
minimal shear...but isolated severe storms are possible given the
instability and dcape approaching 1000 j/kg. Convection diminishes
through late evening...but returns overnight as the east to NE flow
strengthens. Highs today will again rise into the 90s outside of the
mountains and middle 80s for the valleys. Lows will be above normal.
Short term /Saturday through Sunday night/...
at 230 am EDT Friday...on Saturday morning a positively tilted
upper ridge will extend from Texas to New England...while a an upper
trough extends from the western Atlantic to the Carolinas and Georgia. By
Sunday an upper low closes of near the SC coast...south of the
persistent upper ridge. Weak middle level energy rounding the upper
low will move inland from the coast to the southern Appalachians.
At the surface...on Saturday a ridge of high pressure will be in
place along the eastern Seaboard. Model data shows a lack of
isentropic upglide over the ridge...and even low level flow lacks an
orthogonal component into the Blue Ridge. Elevated instability will
be present however...supporting convection that will be maximized
during daytime heating. Temperatures will exhibit a reduced diurnal
range...with maximums below normal...and minimums near normal.
Long term /Monday through Thursday/...
at 230 am EDT Friday...on Monday morning an upper ridge will extend
from northern Mexico to the northeast USA. The models disagree on
the position of an upper low somewhere near the Carolinas and Georgia.
This disagreement becomes more pronounced by Tuesday...when the GFS
has a trough from the Gulf to NC with the upper ridge settling south
of the Ohio River valley...while the European model (ecmwf) has a trough from the Ohio
Valley to the Gulf. By Wednesday the two models start to agree on
the alignment of the trough over the Gulf states...while low
amplitude upper troughing progresses to the northern plains. On
Thursday the northern stream trough moves over the Great
Lakes...coming into phase with the Gulf trough.
At the surface...on Monday a surface ridge will extend along the
eastern Seaboard...with weak troughing off the coast. This pattern
persists into Tuesday. The ridge weakens on Wednesday...while a cold
front moved into the Ohio River valley. This front moves south into
the Carolinas on Thursday.
Modest instability will support diurnally modulated convection
through the extended forecast...with the boundary arriving Thursday
providing a focusing mechanism for convection...a and perhaps more
support for overnight convection. Steering flow remains present for
most of the period...which should keep cells moving. Period of
light upslope flow could enhance convection along the blur ridge at
times...but at this point no prolonged bouts of heavy rainfall are
anticipated. Temperatures will trend upward...from slightly below
normal..to slightly above normal.
Aviation /07z Friday through Tuesday/...
at kclt and elsewhere...generally VFR through the period. Mainly
just some high clouds through early morning. Expect fog in the mountain
valleys but kavl should remain MVFR with few IFR clouds floating
around. Should be another round of 5-8kft cumulus developing near noon and
continuing through the afternoon. Continued prob30 thunderstorms and rain for the
afternoon as scattered convection expected again. Added prob30 for the
evening as convection should linger. Winds will remain north to NE and
light through the period.
Outlook...over the weekend...a moist easterly flow should develop...
bringing better chances for showers and restrictions...in particular
on Saturday. Low clouds and fog will be possible each night in the
07-13z 13-19z 19-01z 01-06z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 96% high 100% high 100% high 100%
khky high 96% high 100% high 100% high 100%
kgmu high 100% high 100% high 100% high 100%
kand high 100% 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)