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Area Forecast Discussion

FXUS62 KGSP 241520

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1120 AM EDT SUN JUL 24 2016

Broad high pressure will linger over the region through mid
week. During the late week, a mid level disturbance is expected to
slowly ripple over the forecast area. Moisture levels will gradually
increase across the western Carolinas and northeast Georgia by the
middle of the week as the region will remain on the warm side of a
stalled mid Atlantic front.


As of 1100 AM EDT, southern tier dewpoints were boosted about a
degree for this afternoon but this still leaves most of Elbert
county with Heat Index values of 103 to 104 on average with just a
sliver of 105 in the southern end. The forecast will mention up to
105 in the county but no Heat Advisory will be posted per
collaboration with the surrounding offices. Regarding the storm
potential, 55 dBZ core heights to 26 kft should be needed for severe
storms to develop.

Otherwise, as a trough in the higher-latitude westerlies continues
to pull away from the East Coast today, upper heights will increase
across the Southeast. In fact, short term model guidance depicts a
small upper level high pressure center over western/ctrl NC this
afternoon. Mid-tropospheric temps are quite warm within this bubble,
as high as -4C at 500 hPa. Convective coverage should be a bit less
than on Sat in light of these warming mid-level temps/poor lapse
rates. Today`s highest chance pops will again be reserved for the
high terrain. Mean cloud-bearing winds are expected to be out of the
E/NE, thus any convection developing over the mtns will be carried
away from the Piedmont, and pops drop off abruptly east of the mtns
accordingly. Having said that, quite a bit of convection developed
across the lower SC Piedmont and Midlands early Sat afternoon, with
attendant outflows pushing north and initiating additional
convection across the heart of the CWA throughout the afternoon.
There are some hints in the latest mesoscale guidance that this
could happen again, albeit perhaps on a smaller scale. Thus, slight
chance pops will be carried outside the mtns, mainly south of I-40.
Sufficient buoyancy and downdraft CAPE will yield a threat for a
microburst or two. Additionally, SW flow in the low levels turning
to E/NE in the mid/upper levels will yield very weak mean flow, so
slow moving cells producing heavy rainfall will also be a concern.
Max temps are expected to be a couple of degrees warmer than on
Saturday in most areas, and heat indices are expected to range in
the 100-104 range, mainly south of the I-85 corridor. Convection
should diminish quickly again this evening, giving way to another
unseasonably warm night.


As of 230 AM Sunday: On Monday, H5 ridge centered over the western
Atlantic as a mid level disturbance tracks west across the northern
Gulf coast. Mostly clear morning sky conditions should result in
steady warming, expected to reach the lower 90s east of the mtns by
lunch. Temperatures are forecast to peak in the upper 80s within the
mtn valleys to mid 90s along and east of I-85. Steady SE winds
should keep dewpoints in the upper 60s to around 70 through the
afternoon hours. The combination of the hot temperatures and RH
around 50 percent should result in Heat Index values around 100
degrees east of the mtns. In addition, the hot and humid llvl
conditions has resulted in interesting forecast soundings Monday
afternoon. NAM soundings across the upstate of SC indicate CAPE
values between 2500-2700 J/kg, LFC a little less that 5 kft, little
to no late afternoon CIN, and around 2000 j/kg of DCAPE. I will
forecast TSRAs to develop over the mtn ridges during the mid
afternoon, then start to slide SE during the late afternoon to early
evening. Areas along and east of I-77 should see the least coverage.
Several of these storms will become quite tall, reaching to around
45 kft. Given the DCAPE and low shear, I would expect several
damaging wet microburst with pulse thunderstorms.

On Tuesday, the center of broad sfc high pressure will shift over AL
as a lee trough develops across the Piedmont. The sfc pattern will
result in light and steady downslope winds from the WSW. Forecast
highs may peak around degree warmer than forecast for Monday.
Dewpoints should range 2 to 3 degrees lower than values from Monday.
Forecast soundings indicate moderate instability with weak capping
east of the mtns. The forecast will continue to highlight high chc
to likely across the TN border counties, fading to chc against the
foothills. Foothill and Piedmont should verify well with schc pops
for SHRAs and TSRAs.


As of 245 AM Sunday...A broad H5 ridge on Wednesday will give way to
a broad trough by Friday and Saturday. I will forecast diurnal chc
PoPs across the CWA on Wednesday. However, the arrival of the trough
would support greater coverage with less diurnal swings in coverage.
I will gradually increase PoPs to high chc to low likely by Sat,
keeping schc pops generally across the mtns during the overnight
hours. High temperatures are forecast to range for 3 to 4 degrees
above normal from Wednesday through the rest of the work week. On
Saturday, high temperatures are forecast to range 2 to 3 degrees
above normal.


At KCLT/KAND/KHKY, With an upper ridge building over the area and
warming temps aloft, chances for convection appear to be at their
lowest in several days. Although isolated cells are expected this
afternoon, the coverage should be sparse enough to preclude any
convective mention attm. Winds are expected to remain light S/SW
through the period.

At KAVL/KGMU/KGSP, isolated to scattered convection is expected to
develop once again Sunday afternoon, although coverage may tend to
be a bit less than in recent days. The best coverage should be over
the mtns, so a VCSH and PROB30 for TSRA is limited ti KAVL for the
time being. Fog will probably redevelop in the mtn valleys tonight,
although timing and the degree of restriction is still highly
uncertain. MVFR conditions should be good enough at KAVL for the
time being.

Outlook: Isolated to scattered afternoon/evening showers and
thunderstorms will continue across the mountains/piedmont through
mid-week, with coverage increasing Tuesday into Wednesday. Morning
fog and low stratus will be possible each day in the mountain
valleys and also in locations that receive heavy rainfall the
preceding afternoon/evening.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
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 100%
KHKY       High 100%     High 100%     High 100%     High  94%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High  94%

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      96 1983     68 1985     71 1934     52 1966
   KCLT     100 1983     73 1938     78 2010     59 1947
                1952                    1883
   KGSP     101 1952     70 1985     79 2010     59 1904


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      92 2010     68 2000     70 2012     51 1895
                2005                    2011
                1987                    2010
   KCLT     101 2010     69 2000     79 2010     62 1947
   KGSP     100 1995     72 2000     77 2010     57 1911





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