Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 210243

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
943 PM EST Tue Feb 20 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.


930 PM Update...Re-aligned and lowered PoPs again based on latest
trends. Some sprinkles and drizzle is noted on the comp rad but no
measurable precip so far. Expect some isol -ra across the srn BR
overnight. Min temps were adj a bit and remain well within record
high min values. Dense fg is still possible overnight.

630 PM Update...Made some downward adjs to PoPs this evening as
moisture remains rather shallow within weak lift. Added patchy
drizzle most locales aft 06z til 16z. Winds could be less stagnant
overnight than this morning...but dense fg is still a decent
possibility outside the mtns with dry air persisting abv h85. With
good insol lasting a few hrs temps will be adj up
mainly across the Upstate and ern piedmont.

As of 245 PM EST Tuesday: Insitu wedge has been very gradual to
erode today as a warm front to the south has slowly moved northward
into the southern most portions of the FA this afternoon. Though
areas of dense fog from earlier today has great improved, isolated
areas of lingering fog persist this afternoon, mainly just east of
the escarpment, along with isolated patches of light rain/drizzle.
Otherwise, mixing with WAA is not only helping lingering fog to
disperse, but for persistent BKN/OVC stratus that we`ve seen today
become more SCT/BKN in nature. With increasing breaks in the clouds,
temperatures continue to rise this afternoon into the mid to upper
60s/around 70 degrees across most of the FA. While we could see
temperatures climb another degree or two before all is said and
done, overall we`ve likely reached our max temperatures for the day.

Into tonight, southwest flow will continue to infiltrate in across
the region through into Wednesday with a deep upper trough situated
across the western US and strong sfc high pressure just off the
Southeast coast, overall little change to the synoptic setup from
yesterday. As the wedge continues to gradually erode tonight,
temperatures will reach near record max low temperatures overnight,
as will be the case over the next several days (see the Climate
section below for more information). Latest fcst soundings continue
to support fog redevelopment overnight, with lingering stratus as
well. Attm, do not anticipate dense fog to be as widespread as it
was last night through into early this afternoon, but nonetheless,
would not entirely rule out patchy areas of dense fog. Thus, a Dense
Fog Advisory may be needed for portions of the FA again tonight into
Wednesday morning. Otherwise, expect clouds to increase, again,
overnight and persist well into Wednesday with gradually increasing
rainfall chances coinciding with increasing low level moisture ahead
of an approaching cold front from the west. This along with upslope
flow, have kept with a gradual increase of PoPs overnight into
Wednesday, with the higher PoPs through the near term forecast
period confined to areas across the Balsams back into the northeast
GA mountains. Increasing instability into Wednesday afternoon, would
not entirely rule out a few isolateD thunderstorms through into the
evening hours, mainly across the western portions of the FA. Warmer
temperatures are expected on Wednesday, with temperatures nearing
record high temperatures for Greenville and Charlotte.


As of 230 PM EST Tuesday: A persistence pattern will remain in place
Thursday through Friday, with strong high pressure lingering off the
southeast coast, and a deep moisture fetch continuing west of the MS
Valley. Over our region, light south to southwest upslope flow and
continued sub-800 mb moisture will produce scattered showers across
the southern mountains through the period, and contribute to partly
to mostly cloudy conditions. 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 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. Will shade northern tier temps toward the cooler guidance
just in case. Very limited instability appears evident south of the
wedge front, so will avoid any thunder mention for now. Otherwise,
expect just isolated to scattered showers through the period. Maxes
will continue some 15 to 20 degrees above climo most areas, with
mins about 25 degrees above climo.


As of 230 PM EST Tuesday: It looks like the Spring-like weather will
continue into the weekend courtesy of the SW flow aloft between the
large upper anticyclone centered over S FL and the nrn Bahamas, and
the upper trof moving across the 4 corners/Srn Rockies then lifting
out over the Plains Saturday night. This pattern will keep temps
running on the order of 10-15 degrees above normal at least into
Sunday, along with moisture moving out of the Gulf of Mexico. A
moist S/SW upslope flow will keep clouds and the possibility of
a few showers in the forecast thru Saturday night but this will
not be close to a washout by any least not until a
cold front approaches on Sunday. The passage of this front is the
big forecast problem for the medium range. The 12Z run of the GFS
has the frontal passage happening later in the day as a dampening
short wave lifts NE across the eastern Great Lakes, which generally
agreed with the 06Z GEFS timing. However, the ECMWF does not have as
clean a fropa...with its solution taking place later...late Sunday
night or early Monday. Even the GFS agrees, though, with bringing
another area of mid/upper forcing across the region on Monday,
smearing a precip chance back across the region on the back side of
the front. Thus, precip chances ramp up Sunday...into the Likely
range west...but then only slowly decrease through Monday. Not a
big change in air mass with this one, at least not initially, and
the overall pattern remains low amplitude, so temps are knocked
down to levels merely ten degrees above normal. Tuesday was kept
dry with upper ridging and high pressure building in.


At KCLT and elsewhere: Another pessimistic set of TAFs in store for
all sites. Low level moisture will continue to advance toward
the region from the south and become trapped beneath layer
aloft. CIGS will therefore drop during the overnight to IFR/LIFR
and VSBY will also drop into the IFR range. Not thinking a high
chance of dense fg...but it is possible and aft 09z all sites
except KAVL. Will include VSBYs just abv or in the high LIFR

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...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       Med   79%     Low   45%     Med   73%     High  97%
KGSP       Low   58%     Med   62%     Med   68%     High  85%
KAVL       Med   62%     Low   58%     Med   70%     High  90%
KHKY       Med   66%     Med   79%     High  82%     Med   78%
KGMU       Med   61%     Med   68%     Low   58%     Med   75%
KAND       Low   59%     Med   62%     Low   45%     Med   70%

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      75 1939     26 1908     50 1951      4 2015
   KCLT      77 2014     31 2015     59 1939      7 2015
   KGSP      75 2014     33 2015     57 1939      9 2015


  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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