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 200557

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1257 AM EST Tue Feb 20 2018

High pressure off the East Coast will provide a warm, moist
southerly flow through the middle of the week. Another cold front
will descend from Tennessee by Thursday. This front will stall out
and linger just north of our area next weekend. Chances for rain and
well above average temperatures will remain through the weekend.


As of 1250 AM: Still areas of fog with patchy dense fog across the
piedmont. May need to add the NC zones along the eastern escarpment
into the DFA, as the escarpment may be obscured with the low
ceilings. Otherwise, forecast is on track.

1045 PM Update...An update to issue a dense fog advisory. Area obs
across the non/mtns are showing 1/2 mile to 1/4 mile visibility.
Dense fog will become more widespread thru the overnight. For
now...the mtn valleys area not having fog issues but they could
around daybreak.

930 PM Update...Made some downward adjs to the PoP grids as no
precip has generated yet in weak isent lift. Starting to see some
dense fg arnd the CLT area and an SPS may be warranted within the
next couple hrs. The atmos remains rather steady-state in the
llvls...but with modest drying deepening aloft...dense fg is still
likely overnight thru daybreak across many locales.

630 PM Update...No sigfnt changes made to the fcst as the atmos is
remaining fairly steady-state within a moist sfc wedge. Expect low
overcast clouds to persist and visibilities to begin to lower thru
the next update. The overnight period still looks pretty good for
dense fg development across the FA as soundings show a saturated and
weakly turbulent BL while dry air deepens aloft.

500 PM Update...Dry air continues to break up cloud cover along the
srn wedge bndry. However...the rate has slowed and llvl moisture
builds back in some areas. Thus...will make minor adjs to the sky
and T/Td grids.

As of 250 PM EST Monday: Wedge in place across the Carolinas has
allowed for mostly cloudy skies to prevail across the area today
with light winds and areas of light rain/drizzle with the aid of
upglide. Per latest radar imagery, most of the rainfall activity has
since tapered off from earlier today, but wouldn`t entirely rule out
areas of drizzle to continue into tonight, especially along the
escarpment. In most areas, temperatures have been slow to climb to
around normal (low to mid 50s), though some locations around the
outer fringes of the FA have climbed into the upper 50s/around 60
degrees this afternoon where it seems the wedge is slowly eroding.

Southwest flow will continue to infiltrate in across the region
tonight through into Tuesday as a deep upper trough remains situated
across the western US with strong sfc high pressure just off the
Southeast coast. Latest guidance continues to suggest the wedge in
place will erode this evening with a warm front quickly moving
northward. With drier air infiltrating in at the mid levels, expect
low level moisture to increase overnight into Tuesday. This along
with light winds, am expecting fog development overnight to become
widespread, with areas of dense fog (potentially warranting a Dense
Fog Advisory). 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).

As low clouds persist into Tuesday morning, expect fog to be slow to
lift, possibly lingering into late morning, as WAA will aid in
dispersing both fog and low clouds into the afternoon hours.
Temperatures will be slow to warm, but they will warm nonetheless,
with afternoon temperatures climbing above normal, into the lower
70s along and south of I-85, into the low to mid 60s elsewhere
(cooler across the mountains).


As of 2 PM EST Monday: A deep-layer southwesterly fetch will persist
Wednesday through Friday between high pressure anchored off the
southeast coast and persistent height falls across the desert
southwest. At lower levels, upslope flow and continued moisture in
profiles below 800 mb will keep precipitation chances up in and near
the mountains throughout the period, with the highest QPF, though
not substantial amounts, in the southerly upslope flow areas. The
zone of deepest moisture will likely lay over from the northwest
into or near the NC mountains on Thursday before drying up at mid
and upper levels. Diurnal instability will briefly bubble up each
afternoon to permit isolated to scattered thunderstorms in southwest
sections on Wednesday and across the foothills on Thursday.

Low-level moisture, and associated clouds, should remain fairly
persistent through the period. Profiles also look favorable for fog
formation Wednesday and Thursday mornings. There is also some
potential for the front to the north late Thursday to backdoor into
the region Thursday night into Friday, so Friday temperatures will
have quite a bit more uncertainty, especially along the I-40
corridor. Otherwise, expect near-record warm minimum temperatures
some 20 to 25 degrees above climo each morning. Maxes should run 15
to 20 degrees above climo at least Wednesday and Thursday.


As of 210 PM EST Monday: The southwest U.S. low pressure
system/trough will begin to open up over the plains over the
weekend, with the various model solutions maintaining different
strengths of a 500 mb wave propagating east. However, all solutions
have the dampening feature passing mainly north of our forecast
area. Meanwhile, deeper moisture will gradually build over the
weekend in the continued southwesterly flow, with the best moisture
near the cold frontal zone arriving on Sunday. 850 mb flow should
ramp up to 40 to 50 kt by Sunday afternoon, with thunderstorms
possible in the warm sector airmass. Instability currently appears a
bit limited for much severe potential that day, but trends will need
to be monitored.

The main sensible weather differences among the models occur on
Monday. The GFS is faster and drier due to exhibiting more of a
clean fropa south of a more vigorous wave. The ECM stalls the
boundary and brings moisture back fairly quickly over it early next
week. The CMC is slower with the front to start with and would have
PoPs linger into Monday. Will follow a blended approach and keep
isolated to scattered shower PoPs going into Monday. Well above
climo temperatures will continue through the period.


At KCLT and elsewhere: LIFR to VLIFR conditions at all TAF sites
thru the rest of the night and into the morning. A weak in-situ
wedge persists with plenty of BL moisture. Guidance certainly looks
pessimistic for today thru tonight, even though the wedge is
expected to erode further. Fog should lift into a low stratus deck
late morning, then some breaks should form, especially along and
southeast of the AND-GSP-CLT line. Conditions should also improve in
KAVL, thanks to SWLY downslope flow and heating in the mountains.
The sites that will likely stay in the LIFR conditions the longest
will be KGSP AND KGMU. Tonight, with the air mass still very moist,
LIFR conditions like return with redeveloping low stratus and fog
after sunset. Winds will be light thru the period, variable within
the wedge, but favoring a south direction elsewhere.

Outlook: Unseasonably warm and humid conditions are expected to
develop by Tuesday, and 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...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       Med   70%     Low   54%     Med   69%     Med   70%
KGSP       Med   70%     Med   67%     Low   55%     Low   57%
KAVL       Med   64%     Med   74%     Med   78%     High  84%
KHKY       Med   71%     Med   66%     Low   39%     Low   39%
KGMU       Med   67%     Med   64%     Low   46%     Low   46%
KAND       Med   68%     Low   58%     Low   59%     Low   52%

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


GA...Dense Fog Advisory until 11 AM EST this morning for GAZ010-017-
NC...Dense Fog Advisory until 11 AM EST this morning for NCZ035>037-
SC...Dense Fog Advisory until 11 AM EST this morning for SCZ001>014-


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