Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
741 PM EDT Thursday Jul 30 2015
a cold front will continue to move through the area this
afternoon...and settle southeast of the area tonight through Friday.
The front and associated deeper moisture will likely remain confined
along the southeast coastline through the weekend...with slightly
cooler temperatures and much drier air expected over the forecast
area. Low level moisture will gradually return early next week as
another cold front approaches from the north.
Near term /through Friday/...
as of 740 PM EDT Thursday...other than slight increases to middle
chance probability of precipitation along the i85 corridor over the next few hours per
latest cam guidance...current forecast remains on track. Did make minor
tweaks to temperatures/dews and sky to account for most recent Sat/obs.
As of 215 PM...a vigorous short wave trough continues to progress across
the Great Lakes into the northeast states tonight...bringing some
height falls atop the County warning forecast area near the base of the trough axis.
However...overall forcing is fairly weak this far south...as
vorticity is being sheared out. At the surface...a cold front is making
inroads into the Piedmont off the Blue Ridge. Some metars are
reporting a notable drop in dewpoints from the lower 70s to upper 60s.
However...the drier air is still back over central KY/TN. Cape is
decent along and ahead of the front...but deep convergence must be
lacking...because convection has been unimpressive so far given the
instability. I will keep a chance pop through the rest of the afternoon...then taper
probability of precipitation from northwest to southeast this evening.
Overnight...dry air will continue to filter in from the north...thus
ending probability of precipitation. Forecast soundings show lingering moisture under a developing
inversion...so there will be some lingering stratocu through
daybreak...especially along and southeast of I-85. Min temperatures will be a
couple categories cooler than in recent days across the northern
zones...but still above normal across the southern half of the County warning forecast area.
Friday...as an upper trough digs across the Appalachians...dry high pressure
will continue to build in from the northwest. Guidance in good
agreement on deeper moisture being shunted south of the County warning forecast area across
the Gulf states and midlands. So expect a dry day on tap.
Thicknesses do not fall much behind the front...but dewpoints should drop
into the 50s to lower 60s across the entire area during the afternoon. So it
should feel much less muggy. Highs will still be a category or two
above normal...except near normal in the high elevations.
Short term /Friday night through Sunday/...
as of 230 PM EDT Thursday...the weather for the weekend looks about
as quiet and uninteresting as it gets for middle-Summer across the
western Carolinas and northeast Georgia. Temperatures should be
slightly above normal through the period...but the main story will
be the relatively dry air mass. In the wake of the cold front
passage...the high pressure air mass to the north and northwest will be slow to
modify through the weekend. A blend of the models suggests dewpoints
dropping into the 55 to 60 range Saturday and Sunday...which will
drop the afternoon relative humidity down near 30 percent. That combined with some
relatively warm air at middle levels will all but eliminate most of the
potential for positive buoyancy...which means a very low potential
for deep moist convection. Although the remnant cold front boundary
will be close...it should be to the south of the forecast area.
Thus...expect only an isolated shower over the balsams Saturday
afternoon...otherwise the entire area should be dry through midday
Sunday. Will allow for some modification by Sunday afternoon...so a
slight chance pop will be included mainly over the mountains
Long term /Sunday night through Thursday/...
as of 230 PM EDT Thursday...the medium range begins Monday with
slight height rises in the upper trough hovering over the eastern
Seaboard. Monday and Tuesday are marked by continued airmass drying
and low level q-vector divergence...with both major global models
showing only minimal quantitative precipitation forecast response over the forecast area. Model
agreement wanes significantly after Tuesday...as a frontal boundary
swings out of the Midwest. The GFS passes the front through the area
on Wednesday...while the European model (ecmwf) hangs up the boundary over the Ohio
River valley. Quantitative precipitation forecast response is only slight in the GFS due to lack of
deep layer moisture and less than impressive instability...so kept
probability of precipitation to slight chance or lower with best chances over the higher
terrain. The upper trough will continue to hang over the eastern
Continental U.S. Through the end of the period...and the trough axis finally
approaches and forces another more substantial front through the
area late Thursday or Friday. Exact timing of the front will need to
be hashed out as models hopefully come into better agreement later
in the period...though quantitative precipitation forecast response is again not particularly
impressive due to lack of instability. Maximum temperatures will start just
above climatology...and rise a degree or two by the end of the period.
Aviation /00z Friday through Tuesday/...
at kclt...VFR through the period despite weak cold frontal passage this
evening. Initialized taf with vcsh as latest convective allowing
guidance favors development along/south of the i85 corridor through
03z-04z. Confidence is low due to the poor verification of the
guidance over the last 6 hours...thus opted not to include tempo.
Otherwise...the front will slide through overnight with 5-10kt winds
solidly out of the north-northwest through the remainder of the period with some
minor gusting possible around daybreak...however not in taf. Skies
will scattered after any possible convection tonight leading to few low
stratus under high level cirrus by morning. Soundings are rather
dry aloft on Friday thus removal of any high clouds seemed warranted
therefore the remainder of the taf beyond 18z features only low VFR
Elsewhere...VFR and thus similar to that of kclt above with a weak
cold frontal passage occurring this evening. All sites aside for kavl feature
low confidence thunderstorms in the vicinity as the atmosphere is most stable over the
mountains. Otherwise...removed all weather mention from all sites around
the 03z-04z timeframe leading to prevailing 06-10kts north-northwest winds by
morning along with few low VFR stratus and high level cirrus.
Eventually expecting the middle/upper levels to dry leading to only low
level few VFR cumulus by midday at the SC sites with sky clear at the NC sites.
Outlook...expecting generally dry and quiet weather through the
weekend with a gradual increase in chances for showers/thunderstorms
and restrictions for the start of the new work week.
23-05z 05-11z 11-17z 17-18z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% high 100% high 100%
khky high 100% 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)