Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 240610

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
210 AM EDT Mon Jul 24 2017

A cold front will become stationary from west to east across our
region through the middle of the week then dissipate.  This should
result in a little cooler temperature and better chances for rain
over the next few days.


As of 200 AM EDT Monday: Convection continues to gradually weaken as
it crosses into western NC from TN. The piedmont convection has
pretty much completely died off, except for a couple decaying storms
in NE GA. I expect things to continue to die down, as we lose
instability and inhibition increases. Temps look on track.

Otherwise, mountain valley fog, some dense, is expected again and
locations outside of the mountains that receive rainfall may see
some as well. Lows will again be above normal but not quite as warm
as last night.

Convection redevelops Monday as outflow boundaries from the
overnight MCS move across the area. Coverage will be better along
and south of the I-85 corridor where the timing of the boundary
movement will coincide with the higher instability. North of the
corridor instability will be much less leading to only isolated
coverage at best. DCAPE and sfc delta theta-E values while still on
the high side, will not be as high as Sunday. Instability will reach
moderate levels but just barely. Therefore, the chance of severe
storms will be less but not non-existent. Highs will be in the lower
90s outside of the mountain, and while still humid, heat index
values should remain below 100.


As of 200 PM Sunday: A weak and nearly stationary cold front
will remain over central GA and SC Monday night into Tuesday,
immediately south of the CWFA. Aloft, we will remain somewhat
under the influence of the northeast CONUS trough, though
without significant embedded vorticity in play early in the
period. More abundant moisture will be present over the south,
near the front, which could increase cloud cover. But otherwise it
appears conditions will be close to climatology, with seasonably
modest instability and weak shear producing a small pulse severe
threat. Partial thicknesses change little from Monday, so max
temps should be similar.

Tuesday night, high pressure will shift into New England in the
wake of the upper trough. A weak upper low is shown to cut off
and remain over the Carolina coast, and allows enough vorticity
to persist over the area that isolated t-storms still could fire
overnight across mainly the Piedmont. The eastward push of the high
will bring cooler air south into the area, which virtually all
guidance indicates will knock max temps down to a couple degrees
below normal, in conjunction with increased cloud cover. Nonetheless
consensus SBCAPE values remain fairly large given still-elevated
sfc dewpoints and good lapse rates afforded by the upper low. PoPs
peak above climo and pulse threats return once again.


As of 145 PM Sunday: The medium range begins Wednesday evening with
a weak closed off 500mb low over the Carolinas and Georgia. As the
next northern stream shortwave crosses the Great Lakes on Thursday,
it kicks this weak low off to the east with the 500mb trough digging
over the East through the weekend. As the Great Lakes shortwave
moves to far eastern Canada, the associated cold front moves slowly
southeast. This front should be nearing the Ohio River early Friday.
As the front approaches from the north, frontal associated
convection will increase first across areas along and north of I-40
Friday afternoon and then spread across much of the rest of the area
Friday evening. The front becomes stationary west to east across our
region through the weekend. The eventual location of the axis of the
trough next weekend varies among the models. This axis location will
have significant influence on our weather. Also, mesoscale
convective systems are expected to develop near the Rockies or
northern Plains states and track southeast in the northwest 500mb
flow toward our region of the nation. Therefore, our weather will
remain unsettled through the weekend. Temperatures will be near


At KCLT and elsewhere: A challenging set of TAFs for early this
morning, as the boundary layer is very moist across the region due
to earlier rain. Guidance is mixed on how much stratus will be able
to develop. Overall, it looks like patchy IFR stratus is expected
across the Piedmont, especially the NC Piedmont near KCLT. So I will
forecast some prevailing IFR there, but keep just TEMPO for
KGSP/KGMU. As for KAVL and KHKY, a band of slowly dissipating
convection should keep things mixed and limit fog and stratus
potential. However, if things can clear out before daybreak, there
may be some quick fog/stratus development briefly. From there,
things look much quieter across the area. The Upstate and at KCLT
will see enough instability for at least a mention of TS prob.
However, guidance continues to trend lower, so these PROB30 groups
may be cut back or taken out completely if the trend continues.
Otherwise, VFR stratocu deck is expected to develop across most of
the area with a light SW wind, except NW at KAVL.

Outlook: Scattered diurnal convection can be expected each day this
week across the region. Chances for morning fog and stratus will
also be possible each day in the mountain valleys.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       Med   75%     High  91%     High 100%     High 100%
KGSP       High  85%     High  92%     High 100%     High 100%
KAVL       High  93%     High  97%     High 100%     High 100%
KHKY       High  88%     High  94%     High 100%     High 100%
KGMU       Med   78%     High  97%     High 100%     High 100%
KAND       High  97%     High  99%     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:




SHORT TERM...Wimberley
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