Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 181439

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1039 AM EDT Tue Oct 18 2016

Dry and warm high pressure will dominate the region through Thursday
with temperatures flirting with record highs. A cold front will
cross the area Thursday night into Friday with rain shower chances
increasing, especially over the mountains. Dry and much cooler
conditions will likely set up across the area over the weekend.


As of 1030 AM EDT Tuesday:  Deep layer subsidence continues to
dominate the pattern this morning across northeast GA and the
western Carolinas.  Moisture in the low levels has allowed for
sustainment of low clouds across the southwest mtns, as well as
across portions of the SC Upstate.  Am still expecting a bit more
sky cover into the afternoon hours as llv cu builds.  Winds will
remain southwesterly, with a few low end gusts not to be ruled out.
The main story line continues to be the max temps today, which will
approach record levels, especially over the Upstate as the 590dm
ridge builds from the southwest.  All in all, no changes were made
to the fcst with this update as latest guidance remains consistent.
Did tweak t/td and sky to reflect latest obs/sat trends and left
the remainder of the near term as it was for this update.

At 200 AM Tuesday: An upper ridge will progress across the Gulf
States and over the Carolinas today and tonight, while troughs cross
the Bahamas and Upper Midwest, while a surface ridge persist over
our area. Temperatures will run above normal across our area under
the upper ridge. Moist inflow from the Atlantic and Gulf of Mexico
into the southern Appalachians will be limited, as will isentropic
upglide, upslope flow, or vertical lift under and inversion aloft.
These factors will not be supportive of precipitation production.


As of 220 AM EDT Tuesday: Upper ridging will persist over the
southeast on Wednesday as a prominent wave develops upstream over
the plains. Good insolation under the ridge, along with a light
downsloping 850 mb flow, will contribute to well above normal,
indeed near record, maximum temperatures across the region. 850 to
500 mb lapse rates will rebound slightly, but a strong capping
subsidence inversion should persist and curtail the potential for
measurable PoP across the mountain ridges.

The area will remain solidly in the warm sector on Thursday as a
warm front retreats northward through PA and an advancing cold front
reaches the mid MS River Valley. Max temperatures could flirt with
records once again. Meanwhile, a tropical/subtropical low pressure
system northeast of the Bahamas on Thursday should get no closer to
the southeast coastline as it begins to get picked up by westerlies
associated with the vigorous trough approaching from the west.


As of 230 AM EDT Tuesday: The approaching upper trough axis will
move quickly through the Appalachians and the adjacent piedmont
Thursday night through Friday. The ECMWF solution remains 6 to 12
hours faster with the associated cold front and narrow band of
deeper moisture than the GFS, but the consensus timing will still
narrow the window of best PoP down to Thursday night and Friday
morning, with quite limited QPF now expected east of the mountains.
Instability appears marginal for TSRA with the fropa given the
expected nocturnal/early morning timing, but some measure of
instability may arrive with the pre/frontal convection in the far
western mountains Thursday night coincident with briefly improved
wind shear. Confidence remains too low at this point to mention any
strong to severe western mountain thunderstorm threat given the
timing. The cold fropa on Friday should lead to general clearing
through the day with lingering shower PoP paring back to the
northern mountains in upslope flow.

Trailing, channeled 500 mb vorticity will cross the southern
Appalachians Friday night and Saturday morning coincident with brisk
NW flow cold advection. The GFS features better low level upslope
moisture and colder sub-zero 850 mb temperatures, but this might
overdone this early in the season. However, cannot rule out a
Saturday daybreak rain/snow mix at the highest elevations of the NC
mountains. Mixing on the cold advection flow should keep any
mountain frost at bay Saturday morning. Heights will steadily
recover from the west Sunday through Monday as a weak clipper system
moves by to the north. Expect plenty of mid to upper 30s NC mountain
min temps on Sunday morning but will hold off on any patchy frost
mention at this point. Temps then moderate through Monday.


At KCLT: VFR. Scattered low clouds are possible, mainly during the
day. Winds will favor the SSW, with modest daytime gusts.
Dew point depression are not favorable for fog based VSBY
restrictions this morning. Some model guidance favors modest VSBY
restrictions Wednesday morning, but a consensus does not. Convection
potential will be remain suppressed by an inversion aloft.

Elsewhere: Dew point depression have remain elevated at many
locations, and the case for daybreak fog based VSBY restrictions is
not good, especially east of the mountains. Should KAVL fog up, a
LIFR to VLIFR CIG could ensue at the same time. Guidance supports
mountain VSBY and CIG restrictions on Wednesday morning. An upper
level inversion will suppress vertical lift and convection.

Outlook: Warm and mostly clear high pressure will remain over the
region through the middle of the week. The potential for mountain
valley fog and low stratus will return each morning. A front will
move through late in the week, bringing back cool autumn air,
and perhaps restrictions due to cloud cover.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High  97%     High 100%     High 100%     High 100%
KGSP       High  98%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     Med   72%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High  98%     High 100%     High 100%     High 100%
KAND       High  97%     High 100%     High 100%     High  95%

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      85 1938     41 1927     62 2007     26 1943
   KCLT      87 1938     53 1966     70 1881     31 2001
   KGSP      86 1938     53 1966     67 1968     31 1893


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      83 1938     47 1891     61 1910     27 1976
   KCLT      87 1938     55 1976     66 1937     30 2009
   KGSP      87 1941     56 1976     65 2006     32 2009


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      83 1985     42 1961     62 1950     25 1981
   KCLT      86 1926     49 1989     66 1993     30 1972
   KGSP      86 1899     50 1989     68 1894     29 1972




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