Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 190538

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
138 AM EDT Tue Sep 19 2017

High pressure will remain in control of the weather pattern across
northeast Georgia and the western Carolinas through much of the
week, leading to above normal temperatures and generally below
normal precipitation chances. Meanwhile, Hurricane Jose will remain
over the western Atlantic with no impacts expected across the
southern Appalachians and surrounding areas.


As of 130 AM EDT Tuesday:  Updated discussion for 06z taf issuance.
Latest IR imagery and obs favor few/sct mid level stratocu across
portions of the fcst area this morning, generally along the I85
corridor as well as atop portions of the NC piedmont.  Sky cover
is somewhat reduced from this time last night, thus guidance
seems to be picking up on slightly improved chances for early
morning fog along the I77 corridor, as it did this time yesterday.
Therefore favored such in the latest update, yet kept any/all visbs
for these zones above DFA criteria with overall coverage uncertain.
Otherwise, with some of the mtn valleys fogging up as expected,
no other changes were needed at this time.

As of 1025 PM: A narrow ridge will remain over the southern
Appalachians and vicinity through Tuesday. This will partially be
reinforced by Hurricane Jose as it continues to move north over
the open Atlantic, not far off the NC/VA coast. Another round of
fog/low stratus is expected to begin developing after midnight,
with observational and numerical guidance trends indicating that
coverage of the goo should be similar, if not a bit less than on
Monday morning. Mins will be in the mid 50s mountain valleys and
lower to mid 60s over most of the Piedmont.

The ridge will weaken a bit Tuesday as a shortwave moves into the
mid-upper Ohio Valley. With reduced subsidence, thermo profiles from
the models indicate deep convection is a bit more likely throughout
the CWFA. That said, with no significant forcing mechanisms, the
models do not spit out much QPF over the area overall, keeping
what they do produce over the mountains/foothills; PoPs reflect
this. Max temps will be a degree or so warmer than today, 1 to 2
categories above climo.


As of 230 PM EDT Monday: Guidance in good agreement with a weak
upper trough developing over Carolinas through the Short Range. A
series of weak short waves will rotate through the trough and across
the area Wednesday and Thursday. At the surface, a weak lee trough
develops and remains in place both days. The atmosphere becomes
unstable as mid level lapse rates steepen. However, instability
remains weak with LFC levels staying relatively high as low level
moisture increases but not significantly. Therefore, still expect
the diurnal convection with the best chances to be across the
mountains where the instability is more likely to be tapped with
lesser chances elsewhere. Thursday has a better overall chance than
Wednesday. Highs will be nearly steady 5 to 10 degrees above normal
while lows 5 degrees above normal Wednesday morning rise a couple of
degrees Thursday morning.


There has been very little change to the forecasted pattern
and sensible weather since the overnight package which means we
continue to expect very pleasant conditions across the area through
at least early next week.  By Friday the region is forecasted to
be within a region of weak upper-level troughiness that extends
from the central Gulf Coast towards the closed upper-level low
associated with TC Jose off the New England coast.  With the spine
of the surface high pressure ridge running down the Appalachians,
a light easterly (upslope) flow combined with support from the
upper-level weakness will result in a slight chance for afternoon
showers across the favorable mountain slopes through Saturday.
Temperatures will remain a few degrees above normal.

Towards the end of the weekend into early next week, guidance is
still suggesting Hurricane Maria will move NW and then due N across
the far Western Atlantic underneath a sprawling upper-level ridge
over the eastern ConUS.  With the upper-level ridge overhead and
Maria off to our SE, the region will experience subsident/clearing
skies, near zero precip chances, and light NEly flow. While
temperatures will remain slightly above normal, dewpoints will
pleasantly drop into lower to middle 50s across the mountains with
upper 50s and lower 60s east of the mountains.


At KCLT and Elsewhere: Conditions very similar to mornings past
as VFR is expected to dominate aside for chances of patchy ground
fog and possible cigs across portions of the NC piedmont, as well
as in the mtn valleys.  Once again guidance seems to be picking
up of fog development along the I77 corridor as it did yesterday
morning, however given less stratocu in place, think chances are
little better for such as does the guidance given that 4 sources
favor it.  Therefore, opted to include prevailing 6sm at KCLT around
daybreak with a 2hr tempo for MVFR fog and sct008. Further north
at KHKY, hit them a little harder with prevailing 5sm, tempo`d
to 3sm sct003. As for KAVL, went with very similar conditions to
KHKY with MVFR tempo`d to IFR, albeit with lower confidence given
min temps are fcst to fall just to the xover temp.  Otherwise,
the remaining sites should stay restriction free with occasional
passing of low/mid stratocu, with all sites favoring light nely/ely
or calm flow.  Moving into the daylight hours, high pressure will
remain in control of the pattern as it`s center shifts slightly
south, possibly setting up nearly atop the region.  Therefore all
sites remain dry with llv moisture sufficient for widespread fair
wx cu amidst light/vrb flow.  Chances for convection will be a bit
higher across the terrain today as upper heights fall slightly,
however kept any wx from KAVL at this time.

Outlook: Chances for diurnally favored showers and possibly a
thunderstorm will increase each day this week.  The best chances
look to be Thursday and Friday as flow veers easterly and marginal
moisture advection returns across the region.  That said, the best
chances for restrictions will be from early morning fog across
the northern NC piedmont/foothills, as well as in the mtn valleys.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       High 100%     Med   75%     High 100%     High 100%
KGSP       High 100%     Med   75%     High 100%     High 100%
KAVL       High 100%     Med   75%     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%     Med   75%     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:




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