Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
240 PM EDT Monday Jul 6 2015
a broad upper ridge will strengthen and migrate over the southeast
into the weekend. Shower and thunderstorm chances will favor the
afternoon and evening. Temperatures will increase above normal
Near term /through Tuesday/...
at 230 PM Monday...for the remainder of the afternoon...expect scattered
convection to increase across the southern upstate by middle afternoon
along the axis of best instability in the vicinity of the Lee
trough. Latest hrrr develops scattered rain showers/thunderstorms and rain northward by late
afternoon into the eastern upstate and the NC Piedmont. So will also
have somoe scattered probability of precipitation there. Can't rule out a few strong to severe
storms as convective available potential energy have increased to arond 2000j and some dry air noted
in middle levels. Activity should wane with loss of heating this
In regard to the picture...the remnants of the upper trough was
gradually lifting to the NE along with a lobe of vorticity noted in
the infrared imagery. This weak forcing should move NE of the western
Carolinas early tonight. In its wake...a weak area of surface high
pressure will build over the area tonight. Hence for the
overnight...it should become mostly clear with some fog developing
in the mountain valleys. Minimum temperatures will be mild with lows in the
upper 60s to around 70 outside the mountains...with upper 50s to middle
Tuesday is shaping up to be a typical July day with plenty of
sunshine and very warm temperatures. Differential heating and weak
upslope flow in the mountains will trigger scattered afternoon
thunderstorms there. It looks like the remainder of the area should
remain dry except perhaps for the foothills where some mountain
storms may drift in late in the day. Maximum temperatures will be a couple
degrees above climatology.
Short term /Tuesday night through Thursday/...
of 230 PM EDT Monday... the short term part of the forecast still
continues a theme for the retrogression of the Bermuda high into our
forecast area (fa) Tuesday night and Wednesday...albeit not yet
firmly entrenched. The upper air pattern then takes on a west-southwesterly look
at that time...with packets of energy moving through the flow...
especially on our northern and western periphery.
Convection Tuesday night in the mountains should wane with loss of
heating...although along the Tennessee/North Carolina state line a
few cells may try to hold on a little longer with weak forcing
Meanwhile on Wednesday...there appears to be enough instability...
and heights have not reached their apex yet...plus tail of energy
packets (dpva) moving through the mean flow...for a chance pop
forecast in the mountain and slight chance elsewhere. We just need
to keep an eye on any convection north of our region...in a waffling
frontal pattern...trying to turn southeastward toward our northern forecast area. The
NAM subtly implies something like this heading off to our east...
therefore a note of caution.
Once again convection will wane Wednesday night. It appears ridging
aloft will be building in full force Thursday. We have kept the probability of precipitation
on the very low side...basically trying to emphasis the higher
terrain locations. We were a little concerned with the Lee side
troffing providing a weak focus around the region...thus probability of precipitation just
into the slight category...which fits well with our neighbors.
We have followed the temperature profile of the models which bring
temperatures up during this part of the cycle...as ridging and heat
begin another surge.
Long term /Thursday night through Monday/...
at 200 PM EDT Monday...on Friday an upper ridge will extend from the
Gulf states to the Great Lakes. The ridge amplifies almost to Hudson
Bay on Saturday...then retrogresses to the Southern Plains by
Sunday...and to the southern rockies by Monday.
At the surface...high pressure will be centered over the southern
Appalachians on Friday...with a Lee trough over the Piedmont...while
a stationary front resides over the Ohio River valley. On Saturday the
western portion of the front dips south into NC...but by Sunday it
is expected to return north as a warm front. Monday features a an
improved pressure gradient and resulting westerly flow...as the
retrogressing upper ridge allows for East Coast troughing and a dip
of the westerlies to our latitude.
Instability is expected to be limited early on under the upper
ridge...although no capping inversion is depicted in model
soundings. As the upper ridge slides west...more robust instability
appears by the weekend. Steering flow will be quite light under the
ridge...but improves as the ridge departs and winds pick up with
East Coast troughing. Temperatures will run above normal...with a
slight decline late in the forecast as heights fall aloft with the
departure of the ridge.
Aviation /19z Monday through Saturday/...
at kclt...main concern is whether any convection will affect the
airfield this afternoon and/or early evening. Best instability axis
is to the S-SW and that is where some radar echoes are currently
noted over the SW upstate of SC. Latest hrrr develops scattered thunderstorms and rain
eastward along that instability axis by 20z and then to the north
circa 21-22z. Confidence still not high enough to go with a temperature
thunderstorms and rain...so will stay the course with a vcsh. No restrictions expected
except if a thunderstorms and rain affects the airfield.
Elsewhere...same concerns as to whether any convection will affect
the airfields. Looks like the SC airfields will have the best chance
as they are closer to the instability maximum over the southern
upstate and the Lee trough. Hence...will carry a thunderstorms in the vicinity at kand/kgsp
and kgmu from about 20-23z. Thunder chances less at kavl and khky so
will just carry a vcsh there. The only other restriction is for some
fog at avl early Tuesday morning. Currently forecasting vsby's to lower
to around 2 miles in fog just befor sunrise.
Outlook...the weather regime will return to a more typical diurnal
summertime pattern through the week. This will mean scattered
afternoon/evening thunderstorms over the area...mainly in the mountains...with
associated restrictions under the heaviest showers...and spotty low
clouds and fog the following morning.
18-24z 00-06z 06-12z 12-18z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% high 94% high 94%
khky high 100% high 100% high 97% 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)