Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
241 PM EDT Friday may 29 2015
Bermuda high pressure will persist across the region through the
weekend and into early next week...with moist southerly flow fueling
scattered afternoon and evening showers and thunderstorms.Saturday
will be the driest day of the weekend...before a cold front
approaches the area by Tuesday and stalls out through the middle of
next week...keeping rain chances above average. A slow drying
out/warming trend is expected by the end of next week.
Near term /through Saturday/...
scattered showers continue to cover much of the northwest half of the
County Warning Area early this afternoon...as a boundary of Atlantic origin
continues to push northwest across the area. Meanwhile...dewpoints
have crashed behind this boundary across the SC midlands and ctrl
NC. Drier low level air should gradually filter into our Piedmont
zones through the afternoon...resulting in minimal buoyancy. Probability of precipitation
will therefore diminish from southeast to northwest with time this
PM. Cells have thus far been moving right along. Thus...localized
Hydro issues will likely be limited to locations that manage to
receive some training cells...especially over and near the high terrain.
Modest buoyancy should keep the severe storm threat rather low.
Convection should diminish quickly this evening. With southeast low level
flow persisting...another surge of Atlantic moisture is expected
to push into the area toward daybreak...and this could result in
some isolated showers near the Escarpment...but will likely be
manifest more as expanding low cloud cover. Min temperatures will be near
to slightly above normal.
Saturday...other than persistent weak upslope flow and scant low
level moisture...not much to hang one/S hat on in terms of the
convective potential. Instability parameters from forecast soundings
are rather pitiful for late may...owing to weak lapse rates/fairly
warm temperatures aloft resulting from rising heights. Nevertheless...
there will be some degree of buoyancy...and combination of upslope
flow/diff heating should allow for a few cells...mainly in the form
of showers to form near the high terrain during the afternoon...and
near-climatology probability of precipitation will be advertised.
Short term /Saturday night through Monday/...
at 2 PM EDT Friday...on Saturday evening an upper ridge will be near
Bermuda...while and upper trough will be moving from the plains to
the MS River Valley. The trough crosses the MS River Valley on
Sunday night...reaching the Ohio and Tennessee River valleys on Monday.
Shortwave energy moving through this trough remains to our west until
Monday...when a shortwave crosses the southern Appalachians late in
At the surface...a cold front will slow while crossing the Ohio and
lower MS River Valley on Saturday night. This front reaches the
southern Appalachians by early Monday...then moves very little
during the day. Instability is expected to increase along and ahead
of this boundary on Sunday...and shear is expected to follow suit on
Monday...supporting an increasing chance of convection. Low level
flow will be veer from light SW on Sunday...to slightly greater but
nearly parallel to the Blue Ridge on Monday...limiting the upslope
flow component. Isentropic upglide will be largely lacking.
Precipitation amounts will be greatest where thunderstorms move
slowly in weak southerly steering flow on Sunday...mainly against
the Blue Ridge...and where they train in better SW flow on Sunday.
Temperatures will run slightly above normal.
Long term /Monday night through Friday/...
as of 230 PM Friday...model consistency at the beginning of the
medium range is relatively good. The period starts Monday night with
an upper trough and associated surface front just to the west of the
southern Appalachians...with a rather broad upper low over the
MS/la Gulf Coast. The frontal boundary meanders slightly to the
east...and remains stalled over our area through Tuesday night. A
moist airmass will remain in place over the County Warning Area ahead of the
front...resulting in likely probability of precipitation focused around the frontal
boundary with slightly diurnal trend. A surface high will build
into the northeast on Wednesday...creating a wedge/cad setup by
Thursday that should remain at least through Friday.
Model divergence begins on Thursday...with the GFS now suggesting a
wetter end of the period than the European model (ecmwf). The GFS maintains an upper
level low slowly lifting northward from the Gulf Coast which
would prevent clearing of the frontal boundary from our area...while
the European model (ecmwf) dives the low into the Gulf and allows the front and
its associated moisture to clear by Friday. Went with probability of precipitation just
above climatology with a diurnal peak...weighting the GFS more heavily due
to its better run-to-run consistency. Instability remains meager
through the extended period...so any concerns should be mainly
limited to locally heavy rainfall associated with weak steering
Maximum temperatures will be near or just below climatology at the beginning of the
medium range...and the moist airmass will keep lows a category or
two above climatology...limiting the diurnal temperature range. Highs will
rebound slightly to normal or just above by the end of the period.
Aviation /19z Friday through Wednesday/...
at kclt/upstate SC terminals...winds should eventually settle at southeast
at around 5 kts this afternoon in the wake of northwest-moving boundary.
Lower dewpoints filtering into the area behind this boundary are
expected to result in diminishing chances for convection this
afternoon. Thus...all vcsh/thunderstorms in the vicinity were removed from the forecast.
However...a stray shower cannot be ruled out...especially over the first
couple of hours of the forecast period. Otherwise...another boundary
of Atlantic origin is expected to push into the area overnight...
bringing another wave of low level moisture. Weak upglide/upslope
flow is expected to result in expanding low clouds toward
daybreak...especially near the Blue Ridge/upstate SC terminals. The
forecast has been maintained at lmvfr for now...but cannot rule out
At kavl/khky...showers/possbl thunderstorms will persist in the vcny
of these two terminals for the next couple of hours...with diminishing
chances expected thereafter. Tempos are carried through 19/20z for
rain showers and MVFR conditions. Weak upglide/upslope is expected to result
in expanding low clouds toward daybreak. The forecast has
been maintained at lmvfr for now...but cannot rule out IFR
Outlook...moist SW flow will continue to affect the terminal
forecast area through this weekend...as a cold front lays over to
the north of the area. Expect pockets of morning fog and/or stratus
most days...with continued chances of afternoon/evening rain showers/thunderstorms and rain each
18-24z 00-06z 06-12z 12-18z
kclt high 100% high 100% high 100% high 86%
kgsp high 100% high 100% high 88% high 86%
kavl high 100% high 100% high 94% high 87%
khky high 100% high 100% medium 73% high 94%
kgmu high 100% high 100% high 94% high 90%
kand high 100% high 100% medium 66% high 84%
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)