Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 262042

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
442 PM 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 430 PM EDT Tuesday:  Isolated/Scattered convection continues
across the region as the atm remains unstable thanks to modest
daytime heating and improved mid level lapse rates, compared to
days past.  Speaking of heat, temperatures seem to have peaked
regionwide with the most elevated levels residing along/south of
the I85 corridor across northeast GA, the SC Upstate, and the NC
piedmont, where readings in the upper 90s atop lower 70s dewpoints
work to yield heat indices approaching 104-105.  These levels will
likely remain brief, especially as convection works across the area.
As for the convection, latest SPC mesoanalysis continues to indicate
impressive DCAPE about the region, especially along the I85/I77
corridor region where values approach 1200j/kg.  Therefore, still
think that any deeper convection will present damaging microbursts
as the primary threat, as well as brief heavy rainfall and cloud to
ground lighting.  For the fcst, opted to adjust pops/t/td to account
for recent trends, and left the rest as it was for this update.

Previous Discussion:  The large 500 mb high moves little thru
Wednesday, but weakens slightly, as a series of shortwaves
try to flatten the northern side of the ridge. Meanwhile, a
quasi-stationary front remains draped along the Ohio Valley to
the northern Mid-Atlantic.  The convective trends are similar
to yesterday, perhaps a tad slower, and mainly confined to the
high terrain so far. Guidance still in agreement on scattered
showers and storms propagating/developing east into the Piedmont
late afternoon into early evening.  PoPs were changed little from
previous forecast in showing these trends. Severe threat still looks
marginal, but SBCAPE on the mesoanalysis page is 2500-3000 J/kg with
DCAPE 800-1200 J/kg.  So a few pulse severe storms will be possible.

Convection should wane this evening with loss of heating, leaving
a fair amount of debris cloudiness within the weak flow aloft. Min
temps will be generally 5-7 degrees above normal.

The other issue is the heat, with the latest obs coming in with
heat indices a little on the high side. A couple of 105 degrees out
there in the Piedmont at ASOS sites. Wednesday looks similar today.
Perhaps a degree or two warmer, but with a little more mixing
out of the dewpoints. The latest heat index forecast is in the
96-104 range again across the Piedmont during the hottest part
of the day. A heat advisory will be considered for Wednesday,
but will allow the midnight shift to make the final call.

Otherwise on Wednesday, the moisture plume will actually lift back
north slightly, as result in convection being more confined to the
mountains and I-40 corridor. The GA/SC piedmont may not see much
of any deep convection, as weaker mid-level lapse rates pivot
around the the ridge from the south. So will feature a tighter
PoP gradient from less than slight chc PoP in the lower Piedmont
to likely along the NC mountain peaks.


As of 230 PM EDT Tuesday: Not much change to the overall synoptic
pattern from what we`ve been advertising the past few days. The
subtropical ridge will continue to dominate, with moisture
associated with a tropical weakness moving onshore today moving up
the Lower Mississippi Valley at the start of the period. Meanwhile a
broad shortwave will push across the northern tier of the country,
pulling the moisture associated with the Lower Mississippi weakness
to the north toward the Ohio Valley. Surface high pressure will
continue to pump a warm and moist air into the region with in
general a fairly typical summertime pattern continuing, but with the
additional moisture creeping into northwest zones from the
approaching wave/front. Additionally, a lee trough progged to
strengthen tomorrow will continue into the short term, which will
provide additional focus for convective development. Deep layer
shear will marginally increase with the approach of the shortwave,
and combined with healthy sbCAPE values between 2000-3000 J/kg, the
continued Marginal Threat outlined on the SWODY3 for northern zones
looks good. As has been the case, low-level lapse rates will
continue to support isolated wet microburst threat, but mid-level
lapse rates not high enough for much in the way of hail concerns.

As we push into Friday, vort max should ride up the southwest flow
aloft ahead of the wave, with the GFS farther south with an area of
enhanced QPF, more over the northern mountains, but the ECMWF
farther north up in WV. Either way this doesn`t help the Upstate and
other areas in continued drought, but with the additional synoptic
lift, could certainly see more widespread coverage across NC. Have
not reflected the GFS solution in pops for Friday and will have to
reevaluate as operational guidance comes into better consensus.

Temperatures will remain a category or so above seasonal normals,
but could be adjusted further one way or another depending on model
evolution of precipitation/cloud shields. Humidity will remain high
with areas in extreme southeast zones continuing to flirt with heat
advisory levels, though should see some minimal improvement on


As of 200 PM Tuesday...The broad scale pattern will not change much
over the ext range. An h5 trof axis remains west of the fcst area
and will likely get pulled slowly NE late in the period. This will
advance a weak sfc front toward the CWFA...perhaps pushing
into/across the mtns by Mon. The flow remains weak and generally
w/ly within the h9/h7 mech lift along with enhanced llvl
moisture from the nearby front will support above normal pops across
the higher terrain. Downsloping in the lee will help suppress convec
activity...thus near normal pops will be maintained over the
non/mtns. Warm temps continue in a relatively stagnant pattern with
max temps will reaching around or a couple degrees above normal each
day. Mins will also be held a cat or so above climo.


At KCLT and Elsewhere: Convection getting a slightly slower start
than yesterday, and is mainly confined to the ridgetops so far.
However, guidance still in good agreement on there being enough flow
to steer some of the activity to the east into the Piedmont,
especially along and north of a line from GMU-GSP-UZA. So I will
continue to keep a TEMPO at KCLT starting at 21z, which is a little
earlier than previous thinking. The other sites will feature VCTS
during the afternoon and early evening. Winds should favor a SW
direction, except NW at KAVL, and variable around TSRA. Later
tonight, there should be a fair amount of debris cloudiness
lingering well into the night. And not expecting much fog/stratus.
However, with expected better coverage of rain in the mountains than
last couple days, KAVL may have a better shot at some restrictions
late tonight. Similar conditions are expected across the area for

Outlook: A plume of deep moisture will gradually build across the
western Carolinas and NE GA through the late week. SCT SHRA and
TSRA 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...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  91%     High 100%
KHKY       High 100%     High 100%     High  95%     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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