Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 261843

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
243 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 200 PM...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...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  94%     High  97%
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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