Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 261438

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1038 AM EDT TUE JUL 26 2016

Broad surface high pressure will linger over the Southeast, before
sliding offshore as a surface low develops and moves northeast
across the Midwest and Great Lakes regions. A surface front will
remain off to our north and linger within a region between the Ohio
Valley, lower Great Lakes, and Mid-Atlantic regions. This front may
finally move into our area early next week.


As of 1030 AM...A 594 dam high at 500 mb remains nearly stationary
over SC/GA today, while a plume of deeper moisture along its
northern periphery punches through the central Appalachians. The
southern edge of the plume is expected to make some inroads into the
NC zones this afternoon. This will provide plenty of moisture for
convection, but should limit DCAPE there. south of the NC border,
the air mass will be drier, and guidance is in good agreement on
only isolated convection at best. However, if any storms can manage
to obtain an icy updraft, higher DCAPE will provide for a wet
microburst threat. The Day 1 marginal risk associated with the
moisture plume includes only the NC zones, though. With all that
said, the current forecast looks on track, with chance to likely
PoPs in NC, and slight chance to low-end chance in GA/SC. Temps will
be a degree or two cooler than yesterday, but with dew points
possibly a degree or two higher. So expect similar heat indices to
yesterday (generally 96-104 across the piedmont). We will mention
the hot heat index values and thunderstorm potential in the HWO.

Tonight, NAM indicates that deep convection will begin to gradually
dissipate during the mid evening. Coverage of TSRAs/SHRAs east of
the mtns should come to an end one to two hours after midnight. A
few SHRAs may linger across the western NC mtns well into the late
night hours. Low temperature are forecast to range from the upper
60s within the mtn valleys to the mid 70s along and east of I-85.


As of 300 PM Tuesday: The subtropical ridge will remain the dominant
feature across much of the southern half of the Conus at the start
of the short term period, with an upper level high centered near the
SC Coast, and a weakness in the ridge across the lower Miss Valley.
A weak tropical disturbance is expected to develop within this
weakness, and become absorbed in the westerlies by mid-week, as an
area of height falls spreads into the northeastern quadrant of the

On Wednesday, a weak lee trough and differential heating/ridge top
convergence are expected to provide the primary sources of lift for
initiating deep convection. Forecast soundings are seasonably
unstable Wed afternoon, especially across the mountains and the
northern zones. However, the GFS and to a lesser extent the NAM
depict very poor lapse rates and weak instability across the
southern half of the forecast area, closer to the upper ridge axis.
That being the case, and with mean cloud-bearing flow that would
tend to take high terrain convection toward the E/NE, there is
virtually no model QPF response across the Piedmont of Upstate SC
and northeast GA Wed afternoon. Since there still is some degree of
buoyancy, a slight chance pop is retained in those areas, but 30-50
pops (along with ridge top likelies) are reserved for the mountains
and the NC foothills and Piedmont.

By Thursday AM, frontal zone associated with aforementioned northern
stream height falls and tropical moisture plume are expected to
extend from the lower Miss Valley into the eastern Ohio Valley and
Central Appalachians. As vorticity max(es) lift west and north of
the forecast area, the boundary may make a run at the NC mtns by the
end of the day, supporting solid chance to likely pops. East of
there, strengthening deep layer SW flow responding to height falls
to our west actually works to advect even weaker mid-level lapse
rates, lower than 5 C/km per a consensus of model guidance into the
Piedmont. This is bad news for the parched areas of the Upstate and
northeast GA, where probability of precip appears to be 20 percent
at best once again Thu afternoon, only made worse by the fact that a
plume of tropical moisture will be taunting the area from only a
couple of hundred miles away.

It appears the severe weather potential will remain low through the
period, limited to perhaps a small chance of a microburst or two
from pulse-y cells Wed afternoon. Increasing wind fields on Thursday
would yield better chances for upscale organization along cold
pools, but again the weak lapse rates aloft may well preclude
adequate instability for robust convection, even in those areas
where chances for convection are decent. Temps will remain at least
a category above climo through the period.


As of 330 AM Tuesday...Unfortunately for those of us desperate for
rain, a clear consensus exists in the global models that would
maintain a mean upper trough west of the forecast area, with perhaps
even a slight retrogression into the early part of the weekend. This
would spell little eastward movement of the front during this time,
and guidance essentially dries up the deeper moisture with time.
Thus, by the time the front finally does push into area, perhaps
late in the weekend, it just doesn`t have much left to work with.
Nevertheless, with ridge becoming increasingly suppressed into the
western Atlantic, the synoptic pattern will become more conducive to
lift and the boundary should support enhanced coverage of convection
in most areas on Sunday and Monday afternoon/evening. Lower
thickness values should also shave a couple of degrees off of this
week`s hot temperatures.


At KCLT and KHKY: Morning water vapor loop indicates a west-east
band of rich moisture across the central Appalachians and mid
Atlantic states. As the H5 ridge slowly slides SE over the western
Atlantic, the southern edge of the moisture band is expected to
reach the I-40 this afternoon. The environment of higher PWs,
moderate instability, and LFCs around 5.5 kft should yield sct
coverage of deep convection. I will forecast TSRAs to develop
initially across the high terrain, then slide SE with the sfc trof
over the Piedmont during the late afternoon to early evening. I will
highlight the period of convection with a TEMPO at KHKY from 19z-23z
and a PROB30 at KCLT 22z-2z. Otherwise, the forecast will feature
steady winds from the SW and CU bases around 6 kft.

Elsewhere: Conditions should remain similar as discussed above. The
potential for TSRA will develop earliest near KAVL between 19z-23z,
then spreading to the I-85 corridor between 21z-1z.

Outlook: A plume of deep moisture will gradually build across the
western Carolinas and NE GA through the late week. SCT SHRAs and
TSRAs will be possible each afternoon and evening, coverage the
greatest across the mtns. Pre dawn fog and low clouds will be
possible over areas of recent rainfall.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
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  87%
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:



  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      94 1949     72 1911     71 2012     49 1911
                1940                    2010
   KCLT     100 2005     74 1920     76 1992     60 1904
                1940                    1940
                1914                    1936
   KGSP      99 2010     76 1920     76 2005     53 1911
                1995                    1940


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      97 1952     70 1946     72 1936     48 1911
   KCLT     103 1940     74 1926     76 1944     57 1920
   KGSP     103 1940     70 1946     75 2012     54 1911




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