Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS62 KGSP 251430

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1030 AM EDT MON JUL 25 2016

Broad high pressure will linger over the Southeast through the
remainder of the week, supporting plenty of heat and humidity. A
front is expected to remain more or less stationary from the mid
Atlantic through the Ohio Valley.


As of 1030 AM...An upper ridge remains over the Carolinas today,
helping keep things a little suppressed. The 12z GSO/FFC soundings
show warmish mid-level temps, and only moderate instability is
forecast. The 12z NAM has come on board with keeping the Piedmont
largely capped today and tonight. But a few isolated showers and
storms may still develop in the lower elevations east of I-77. The
mountains should see the usual scattered convection starting on the
ridgetops. The NAM and GFS still show large differences in afternoon
dew points. The GFS mixes out the area into the mid 60s, while the
NAM keeps dew points in the 70s. I think the truth will be in
between, and this is in line with the current forecast. So I expect
decent DCAPE and consequently a non-zero wet microburst threat with
any stronger storms. Also, heat indices should stay below advisory
criteria, mainly in the upper 90s to around 104.

Tonight, thunderstorms will gradually dissipate after sunset.
However, a few storms may linger over the mtns through most of the
overnight. Temperatures should slowly cool across the CWA under a
blanket of dissipating debris clouds. Areas of afternoon and early
evening rain may see patchy fog develop.


As of 310 AM Monday, the subtropical ridge will remain the dominant
synoptic scale feature across the Southeast during the short term.
Surface reflection/Bermuda high will support plenty of heat and
humidity across our area for the foreseeable future. A lee trough and
the usual terrain effects will provide the primary source of lift
for initiating deep convection Tue afternoon. Buoyancy profiles are
quite impressive across the mountains during this time, and 50-60
pops appear warranted. There are some hints that surface dewpoints
could mix out outside the mtns in response to westerly flow, but at
least scattered activity should push off the high terrain by as
dewpoints begin to recover by evening.

Instability profiles continues to improve over a larger area on Wed,
while a surface boundary associated with Midwest height falls will
approach the area from the NW. Thus, while more convection is likely
to initiate across the forecast area Wed afternoon, there will also
be an increasing chance for frontal activity to push into the
mountains during the late afternoon/evening. Another round of 50-60
pops will be forecast for the mtns, with 30-40 percent chances
across much of the foothills and Piedmont. Wind shear profiles will
remain weak through the period, thus chances for organized
convection will be small. However, increasing coverage of
convection, along with healthy downdraft CAPE forecasts will likely
result in increasing chances for microbursts into mid-week. Temps
will remain a good 5 degrees above climo through the period.


As of 210 PM Sunday...Little to no change in the pattern or sensible
weather is anticipated late week into the weekend, as Bermuda high
pressure continues to support at least seasonal levels of heat/
humidity/instability, while weak synoptic scale boundary is expected
to remain draped in the vicinity of the Ohio Valley. The only
potential break in the monotony would be a weak disturbance that
global model guidance is trying to develop within a weakness in the
subtropical ridge across the northwest Gulf of Mexico later this
week. Moisture associated with this feature could get advected north
toward the end of the week, as a weak mid-level wave moves out of
the Plains. However, even the more aggressive guidance keeps the
deeper moisture west of our forecast area through Day 7. Overall,
near to slightly above climo pops and near to slightly above climo
temps look to be the most likely scenario for Days 4-7.


KCLT and elsewhere east of the mtns: VFR through the period.
Rainfall coverage was outside of the foothill and Piedmont TAF
sites, potential for fog this morning is low. I will include a
mention of MVFR fog at KHKY based on the latest observation. The
western Carolinas will remain on the western edge of a H5 ridge
through tonight. The sfc pattern will feature a high over the
Atlantic and a shallow trough over the Piedmont. This pattern should
support a light SSW across the region, with periods of calm this
morning and late this evening. Temperatures will begin the day
around 5 to 7 degrees above normal. The warm start and strong
insolation should result in temps in the low 90s around noon,
peaking in the mid 90s by mid afternoon. Hot temperatures and
dewpoints near 70 degrees will yield moderate instability and steep
llvl lapse rates. However, LFC are forecast to range from 6.5 to 6.8
kft and mid level lapse rates generally run at a shallow 5 C/km. NAM
dewpoints appear too high and convection coverage is likely
overdone. Using the SPC SSEO and 4 km WRF, I will limit PoPs east of
the mtns and keep convection out of the TAF.

KAVL: The terminal did not receive measurable rainfall on Sunday. At
10Z, dewpoint depression remained around 2 C. Based on the forecast rate
of cooling through sunrise, it appears that the crossover
temperature will not occur this morning. I will not mention fog
during the early portion of the 12z TAF. Ridgetop convection should
trigger during the mid morning, drifting over the valleys between
19z to 24z. I will highlight the potential for TSRA with a TEMPO
during expected period. Otherwise, winds will vary from calm early
this morning to NW during the morning daylight, SW expected during
the afternoon.

Outlook: Isolated/scattered afternoon/evening showers and
thunderstorms will continue across the mountains/piedmont through
much of the week, with coverage increasing a bit each day. Morning
fog and low stratus will continue in the mountain valleys around
daybreak each day, and also be possible in locations that receive
heavy rainfall the preceding afternoon/evening.

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       Med   68%     High 100%     High 100%     High  91%
KHKY       High 100%     High 100%     High 100%     High  95%
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      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


  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




CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.