Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
755 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/...
as of 735 PM...showers and storms were isolated close to the
Blue Ridge near the upper French Broad valley. Think the downward
trend should continue through the middle part of the evening...
which the forecast generally has indicated well. Temperature trends were much
improved and should be okay through middle/late evening.
Remainder of previous discussion...
In regard to the big 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 /00z Tuesday through Saturday/...
at kclt...VFR conditions are expected through the period. One
interesting feature of note is an outflow boundary seen on the tclt
imagery moving down from earlier convection over the northwest Piedmont.
The boundary appears to be decelerating over northern Mecklenburg County
well north of the airfield so there is some doubt that it will ever make
it as far S as kclt...as there is no remnant convection left to
reinforce its southward movement. Even if it makes it to kclt...the wind
speed should be only on the order 5-8 knots. Have opted to not indicate
a wind shift but will monitor. If it does happen...it will be around
01z and should wash out by 03z. For the rest of the overnight...
expect a light S wind...and some remnant high clouds. On
Tuesday...wind should come up from the S/SW around the time we get a
few cumulus developing late morning/midday. Chance of deep convection
appears to be too remote in the afternoon...so will not mention any
vcsh or prob30 in the taf.
Elsewhere...in the very near term kavl has the best chance for
precipitation...but heating will be lost in short order which should put
the brakes on further development. Will handle this with a thunderstorms in the vicinity for
the first few hours. Otherwise...only some high convective debris
clouds this evening with light S winds around the region. Could be
some Mountain Valley fog at kavl with the middle level drying moving in...so
visibility was taken down to MVFR then IFR by daybreak at kavl. The other
place with some possibility of low visible was kand...which is handled
with a brief MVFR around daybreak. All locations should be VFR after
13z. Similar to kclt...wind should come up from the S/SW with a few
convective clouds developing during midday. Only the NC mountains appear
to have much of a chance of precipitation...so only kavl gets a prob30 for
middle to late afternoon.
Outlook...scattered afternoon/evening thunderstorms are possible over the
area through late week...mainly in the mountains...with associated
restrictions under the heaviest showers. Low clouds and fog could
develop in the morning at places that have shower activity the day
00-06z 06-12z 12-18z 18-00z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 94% 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)