Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 210903

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
503 AM EDT THU JUL 21 2016

A Bermuda high pressure pattern will persist across the region through
the end of the week, resulting in typical midsummer conditions. Hot
high pressure will strengthen this weekend, then a weak cold front
will approach from the northwest early next week.


As of 500 AM EDT Thursday: Convection persists across our southern
zones, continually redeveloping in Laurens County. Have adjusted the
pop trend through the morning, but no other changes at this time.

Otherwise, not much change to the overall synoptic pattern for the
near-term, with the dominant upper ridge over the Plains and
troughing over the NE, leaving us in NW to N flow aloft.
Continuation of a series of upper-level shortwaves/impulses will
continue to work their way from the crest of the upper ridge across
the Great Lakes, diminishing as the flow becomes more diffluent but
with at least some pieces of energy working their way toward the Mid-
Atlantic and Southeast around the eastern periphery of the ridge.

One piece of energy is progged by all the operational models to dip
down towards the Southern Appalachians. With a modest attendant
upper jet streak and of course continued weak upper diffluence, all
the guidance is blossoming convection across the Southeast by the
middle of the day. There are some differences in location, but most
of the CAMs want to develop convection generally S of I-85, with of
course typical summertime convection in the mountains as well. Bufr
soundings show continued steep low-level lapse rates with some
improvement in mid-level lapse rates, though still see a weak
subsidence inversion between 600-700mb. Progs of sbCAPE seem to line
up generally with the QPF progs with best sbCAPEs across our extreme
southern zones, but also do show a spine of increased values along
and just E of the Blue Ridge. SPC SWODY1 still has most of our area
in a Marginal Risk today (damaging winds), and that seems reasonable
and will continue to advertise this threat.

As for temperatures, with the upper energy coming down, expect that
we should see an uptick in sky cover today which may help to keep
temperatures closer to climatological normals, though there is some
bust potential there if clouds don`t fill in quite as much. Pretty
much a persistence forecast for overnight lows tonight.


As of 300 AM Thursday...The large, massive upper ridge will begin to
retrograde slightly, as a series of progressively stronger
shortwaves ride over the top of the ridge and into the Great Lakes
during the short term. It seems the models continue to trend a
little deeper with a developing longwave trough over the Northeast
states for this upcoming weekend. So as a consequence, they are not
advertising quite as strong of heat wave for our area, as previous
days. Still, expect above normal temps and lots of humidity. Staying
on the warm side of guidance, I still get heat indices in the 100 to
105 range Saturday and Sunday, but fewer pixels of greater than 105.
In any case, will continue to mention excessive heat possible in the
HWO. As for convective chances, the upper ridge will build slightly
eastward over the area Friday and Saturday. So shear will be weak
and convection should be isolated to scattered in nature, basically
normal for late July. However, forecast soundings show moderate to
high DCAPE. So pulse severe microbursts will be a threat each day.
Also, the latest GFS/CMC/NAM all show an MCV rounding the ridge and
dropping south from Ohio to the southern Appalachians Friday night
thru Saturday. If we do get an MCS from upstream that may be the


As of 315 AM Thursday...Another shortwave trough will cross the
Great Lakes on Monday, then another on Wednesday. These waves should
weaken the subtropical ridge over the Southeast states somewhat.
Although the medium range guidance diverges on to what extent, the
00z ECMWF showing a deeper eastern CONUS trough than the GFS by Day
7. At the surface, a cold front will gradually slide southeast
across the Ohio Valley and the central Appalachians Monday and
perhaps settle across the CWFA on Tuesday and lingering thru
Wednesday. So temps will trend back down toward normal and PoPs will
trend up with the front in the area. Instability looks decent every
day, but shear remains weak. So expect solid coverage each
afternoon/evening with only a marginal severe threat.


At KCLT: No changes to the KCLT TAF for the 09z AMD. VFR expected
thru the period. SE winds this morning will veer to the SW through
the period, generally 5kt or less. Should see another round of high-
based Cu this afternoon but convection chances too low to add PROB30
at this time.

At Upstate TAFs and KHKY: LGT/VRB winds this morning, trending more
NE, will veer around to SE through the day and eventually SW this
evening, but like KCLT generally 5kt or less. Have continued trend
of PROB30 -TSRA for all sites this afternoon. Should be mainly VFR
but cannot rule out some pre-dawn MVFR fog.  Have added TEMPO to
KHKY to cover this, and will need to watch trends across the Upstate
TAFs through the night.

At KAVL: Similar trend with convection as Upstate sites and kept
PROB30 -TSRA. Big difference will be continued threat of early-
morning IFR to potentially LIFR conditions. Expect mainly VRB winds
but should swing around to a down-valley component this afternoon,
5kt or less.

Outlook: Expect fairly typical midsummer weather with afternoon
showers and thunderstorms through the end of the week. Morning fog
and low stratus will be possible each day in the mountain valleys
and also in locations that received heavy rainfall in the preceding

Confidence Table...

            09-15Z        15-21Z        21-03Z        03-06Z
KCLT       High  98%     High 100%     High 100%     High 100%
KGSP       High  91%     High 100%     High 100%     High 100%
KAVL       Low   55%     High 100%     High 100%     High 100%
KHKY       High  91%     High  94%     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      95 1983     69 1974     71 2015     50 1966
                1952        1938        1999
                1934                    1983
   KCLT     101 1987     73 1880     78 1991     56 2007
   KGSP     102 1952     74 1974     79 1934     59 1966


  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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