Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211800

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
100 PM EST Wed Feb 21 2018

High pressure off the East Coast will provide a warm and
moist southerly flow of air throughout the week as a cold front
stalls and lingers west of the mountains. This front is not expected
to pass through the region until Sunday.


As of 100 PM EST Wednesday: Main update for 18Z TAF issuance
along with minor tweaks to temperatures to coincide with latest
trends as the rest of the near term forecast remains on track.

Otherwise, temperatures have been on a warming trend since the
overnight hours, with current temperatures well in the upper
60s/lower 70s. Though there are some breaks in the clouds as seen
from latest satellite imagery, overall plenty of cloud cover remains
in place overhead this afternoon as light showers continue move
northwest up across the escarpment.

Little change in the synoptic pattern thru the near term, with the
CWFA remaining between a large upper high to the east and deep
trough to the west. Moist LLVL SWLY flow will persist thru the
period, keeping skies cloudy to mostly cloudy. Cloud cover should
scatter out somewhat like it did yesterday, leaving a low-based cu
deck thru the aftn. Temps will be a category or two warmer than
yesterday, and this combined with dewpts in the 60s will result in
some sfc-based instability. CAPE is forecast to range from 500 to
1000 J/kg. But forecast soundings show a mid-level inversion that
should cap convection to under 700 mb (where temps are still above 0
C). So I think thunder chances will remain low. Cannot rule out an
isolated rumble of thunder in the NC mountains, where upslope might
help break the mid-lvl cap, but will not mention thunder for now. In
any case, scattered showers will be possible, with greatest coverage
in the SWLY upslope areas of the NC/GA mountains. Temps will
approach or break record highs at KCLT and KGSP (See climate section

Tonight looks like it will be a lot like the current night, with
plenty of low clouds, patchy fog, isolated to scattered light
showers, and min temps way above normal. Lows look to be in the
upper 50s to lower 60s, which would tie or break high minimums for
Thursday, the 22nd.


As of 325 AM EST Wednesday: A persistent pattern remains in place
Thursday through Friday night with strong high pressure lingering
off the southeast coast, and a deep moisture fetch continuing west
of the MS Valley. Over our area, light south to southwest upslope
flow and continued sub-800 mb moisture will produce scattered
showers Diurnal instability will affect mainly the NC mountains on
Thursday afternoon, with thunder chances best in the extreme
southern Appalachians.

Marginal 850 mb drying is expected late Thursday night through
Friday; however, boundary layer moisture will persist. A back door
cold front will flirt with the northwest NC piedmont Friday, but
model consensus keeps the wedge front just north of the region
through Friday. In fact, the GFS which was bullish on southward
frontal movement has backed off significantly leaving the NAM the
sole model moving the front this far south. That said, even the NAM
keeps the front and the bulk of the colder air north of the area
just brushing Davie County. Precip chances will be limited to the NW
Piedmont Friday morning and the Northern Mountains during the
afternoon. Isolated showers increase across the Mountains into the
NC Foothills and Piedmont Friday night as deeper moisture returns.
Highs will be near records both days. Lows will be above normal
highs and near record high mins as well.


As of 1205 AM EST Wednesday: Circulating around the periphery of
deep layered hipres offshore, the very mild airmass will linger atop
the SE CONUS into the upcoming weekend. Saturday maxes are close to
persistence, 15 deg f or more above climo.  Deeper layer moisture
should continue it`s eastward creep with the associated upward
ramping of pops into solid chance range by later in the day. The
recently posted 21/00 utc op GFS supports the current thinking of a
questionably forced, decently sheared cold fropa Sunday within a
weak instability regime.  Sensible wx will continue to feature
shower coverage becoming numerous west to east acrs the cwfa
beginning Sunday morning. Based on the timing of shower chances,
piedmont max temps are slated to be equally as warm as Saturday,
solidly middle 70s. With the orientation of the llvl boundary
expected to become parallel to the upper flow, and additional energy
progged to ripple up the boundary on Monday, it is probable that an
additional round of numerous showers will redevelop across the
region. Tuesday continues to look dry with encroaching upper ridging
and sfc hi pressure. Max temps should be less mild but still two to
three categories above climo.


At KCLT and elsewhere: A mixture of marginal VFR/MVFR/IFR due to low
cigs is expected through tonight, becoming MVFR/IFR/LIFR overnight
into Thursday due to lowering cigs, areas of fog and VCSH.

Ahead of a slowly eastward propagating cold front, southwest flow
continues to infiltrate plenty of low level moisture in across the
area. While mainly MVFR cigs prevail this afternoon, intermittent
breaks in cloud cover have allowed for brief improvement to VFR in
some locations. At the same time, even lower cigs in other locations
are creating IFR, especially coinciding with areas of light rain
moving northeast up across the escarpment. Overall, expect mixture
of flight restrictions to continue into tonight, with additional low
level moisture allowing for stratus to fill in overnight. As a
result, low cigs and areas of fog will create MVFR/IFR/LIFR through
into Thursday morning with -RA/VCSH at all TAF sites with the
exception of KCLT. Southerly winds will prevail through the forecast
period, around 5 to 10 kts.

Outlook: Unseasonably warm and humid conditions are expected to
persist through the end of the week. Shower chances will be highest
across the mtns, while periodic CIG and VSBY restrictions will be
likely through the week, esp during the late night and morning hours.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       Med   72%     Med   76%     High  82%     High  94%
KGSP       Med   78%     High  85%     High  84%     High  89%
KAVL       High  84%     Low   48%     High  81%     High  87%
KHKY       High  80%     High  80%     High  86%     High  92%
KGMU       High  81%     High  84%     High  85%     High  89%
KAND       Med   75%     Med   72%     High  83%     High  89%

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      77 1986     12 1896     54 1997      8 1896
   KCLT      75 2011     32 1896     56 1997      6 1896
   KGSP      75 1917     35 1978     55 1997      9 1896


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      72 1897     27 1939     54 1897      2 1963
   KCLT      74 1990     33 1963     62 1897     12 1963
   KGSP      76 2011     35 1969     55 1980     10 1963


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      76 1982     29 1989     54 1922     10 1939
   KCLT      76 2012     29 1901     56 1944     19 2009
                1980                                1978
                1962                                1963
   KGSP      76 2012     36 1966     57 1922     15 1963
                1996        1939


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      77 1930     26 1947     50 1985      6 1967
   KCLT      80 1982     26 1889     56 1992     16 1967
   KGSP      79 1982     33 1901     57 1909     15 1967


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      78 1930     17 1967     51 1985     -2 1967
   KCLT      82 1930     27 1967     58 1890      7 1967
   KGSP      79 1930     30 1967     57 1985      8 1967





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