Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
801 PM EDT Wednesday Jul 29 2015
a weak cold front will approach the area from the northwest on
Thursday and settle southeast of the region on Friday. The front and
associated deeper moisture will likely remain confined toward the
southeast coastline through the weekend...with slightly cooler
temperatures expected over the forecast area. Low level moisture
will gradually return early next week.
Near term /through Thursday/...
as of 755 PM EDT Wednesday...as expected...convective coverage has
diminished with further clearing expecting through middle evening with
heating/instability loss. Thus made slight tweaks to account for
such along with current radar trends which indicate only a few
remaining shra/tsra. Also adjusted temperatures and dewpoints to
account for most recent observation...especially for locations that saw
earlier precipitation. Otherwise...forecast remains on track thus no other
changes needed/made at this time.
As of 225 PM...radar shows scattered showers/thunderstorms aligned along
the Blue Ridge and also over the southern upstate along an axis of
higher cape. Cells exhibiting only slow movement to the southeast. With
precipitation. Water around 2 inches...locally heavy rain/flooding is the
main threat this afternoon. Cams indicate that some scattered convection
may linger into the evening hours...but it should dissipate by
In regard to the big picture for the short term. An upper low
deepening over the Hudson Bay will promote falling heights across the
eastern U.S. This will drive a cold front southeast which will approach the
NC mountains by 12z Thursday. The front will then proceed to cross
the western Carolinas and NE Georgia on Thursday.
In regard to the sensible weather...the overnight will feature
partly cloudy and humid conditions with some locally dense valley
fog developing in the mountains after midnight...and mainly just
light fog outside the mountains. Some showers/storms associated with
the approaching cold front may reach the mountains early Thursday
morning...so have probability of precipitation increasing into the chance category there.
Frontal convergence combined with the falling heights should lead to
scattered to numerous thunderstorms developing across the area during
Thursday with the best coverage during the afternoon outside the
mountains. Strong heating and improving lapse rates may support a
few severe storms Thursday afternoon. Storm Prediction Center has most of the area
outside the mountains in a marginal risk for Thursday. Temperatures
will remain above climatology with lows in the 60s mountains to low 70s
elsewhere...and highs from the middle 80s mountains to the lower to middle
Short term /Thursday night through Saturday/...
as of 230 PM Wednesday...the big story for the short term period
will be the establishment of an eastern long wave trough...with the
axis of said trough expected to set up along the East Coast by early
in the period. This should allow the frontal boundary...and
attendant convection to be carried southeast of the forecast area
Thursday evening. While thickness values will not change much in the
wake of the boundary...essentially resulting in near-climatology temperatures
through the period...the main impact will be the introduction of an
unseasonably dry air mass. In fact...dewpoints may mix out well into
the 50s Friday afternoon. The result will be virtually no positive
buoyancy... as depicted by the latest runs of the NAM and the GFS.
Probability of precipitation will therefore be features well below climatology...and in fact below
20 percent across the majority of the forecast area Friday afternoon
and evening. Not much change in the air mass is anticipated through
Saturday...and probability of precipitation remain at 20 percent or less during the
afternoon and evening. Overall...it/S shaping out to be a decent
weekend as far as early August GOES.
Long term /Saturday night through Wednesday/...
as of 205 PM Wednesday...the medium range forecast picks up at 00z on
Sunday with broad upper troffing over the eastern Continental U.S. And broad
upper ridging in place over the western Continental U.S.. this pattern is
expected to remain in place through most of the period with some
deamplification of the upper trough expected by the end of the period
next Wednesday. At the surface...high pressure centered to our northwest will
be over the forecast area at the start of the period and should linger
into early next week...gradually getting weaker. The European model (ecmwf) still
tries to spin up some sort of surface low to our south early in the
period...yet the GFS continues to supress any low development.
Towards the very end of the period on day 7...the long range
guidance suggests that another Canadian surface high will begin to move
into the region from the northwest. As for the sensible forecast...we can
expect mostly diurnal chances for scattered convection each day/evening
with the best chances over the southeast zones. Chances increase a bit for
Tuesday and Wednesday over the northwest zones with better low level convergence
expected. Temperatures will start out right around normal and remain near
normal...if not a few degrees above...through the period.
Aviation /00z Thursday through Monday/...
at kclt...VFR conditions will prevail through this taf cycle with
the possible exception of early morning MVFR br. Initialized taf
with vcsh to account for current rain showers coverage west of the terminal
along with few low VFR clouds. Expecting improving conditions with
heating loss into middle evening thus high clouds prevail through much
of the overnight. Guidance favors MVFR visb with another bout of
low VFR stratus just before daybreak as the moist planetary boundary layer decouples.
VFR will return afterward with a cold frontal passage being the primary focus
of the taf on Thursday. Kept winds SW under developing low VFR cumulus
ceilings through midday before veering flow northwest as the front intrudes
along with thunderstorms and rain mention in the form of prob30.
Elsewhere...VFR through the first few hours of the taf cycle before
guidance favors deteriorating visb at all sites aside for kavl where
both visb/ceilings will fall. As the bl decouples around or just after
midnight expecting the a fore mentioned restrictions to
commence...thus tafs feature MVFR visb at all SC sites with tempos
for IFR at the NC sites through daybreak. As with kclt above...the
primary focus for the taf on Thursday will be the passage of a weak
cold front and any convection it initiates. Therefore all sites see
prob30s for thunderstorms and rain with timing adjustments according to latest cam
guidance. Winds will initialize out of the SW before veering northwest at
around 4-7kts by early afternoon at all sites.
Outlook...high pressure with build in behind a passing cold front
late on Thursday allowing for generally dry and quiet weather
through the weekend. Chances for showers/thunderstorms and thus
restrictions will return for the start of the new work week.
00-06z 06-12z 12-18z 18-00z
kclt high 100% high 88% high 97% high 100%
kgsp high 100% high 94% high 97% high 100%
kavl high 88% low 55% high 87% high 100%
khky high 94% high 94% high 100% high 100%
kgmu high 100% high 94% high 100% high 100%
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)