Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201827

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
127 PM 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 115 PM EST Tuesday: Main update for 18Z TAF issuance along
with minor tweaks made to going temperatures as the rest of the near
term forecast remains on track.

Though the Dense Fog Advisory was allowed to expire at noon,
lingering patches of fog are possible over the next few hours across
the FA as an insitu CAD wedge remains in place across the
Carolinas. Elsewhere, especially along the TN border, clouds are
slowly beginning to erode as seen from latest satellite imagery,
with temperatures almost near 70 degrees across the southern
portions of the NC mountains, including the Asheville area. Areas
east of the escarpment remain under a blanket of clouds, where
temperatures are lower in the upper 50s/lower 60s. Per latest
satellite trends, clouds will gradually erode, potentially allowing
temperatures to reach near 70 degrees south of the I-85 corridor,
before clouds fill back in tonight.

Otherwise, moist SWLY flow will continue atop the CWFA between a
large ridge to our east and deep trough to our west tonight. There`s
just enough vestige of a cold pool across the foothills and piedmont
such that stratus and fog will likely redevelop/expand across the
area after sunset. Dense fog doesn`t look as likely/widespread in
the guidance, but cannot rule out another DFA needed for some
portions of the area thru early Wednesday. Temps will remain way
above normal under clouds and persistent LLVL WAA flow. Min temps
will actually stay above normal afternoon highs, possibly breaking
high minimums for Wednesday morning. As for PoPs, guidance really
wants to ramp up QPF response within the SWLY flow, but other than
some weak upglide and upslope flow, there isn`t much to force
precip. Moisture depth in the forecast soundings does increase
somewhat, so I do allow PoPs to ramp up into the CHC range by
daybreak Wednesday, favoring the areas near the escarpment. Any
precip accums should be very light.


As of 310 AM EST Tuesday: A deep-layer southwesterly fetch will
persist Wednesday through Friday night between upper high pressure
anchored off the southeast coast and a trough over the western
CONUS. Weak short waves ripple through the flow and move near the
forecast area but remain mainly to our north and west. At the
surface, a similar pattern exists with high pressure over the
Atlantic and a cold front slowly moving southeast toward the area. A
moist southerly upslope flow remains in place through the period.
However, the moisture isn`t very deep. Synoptic scale forcing and
low level isentropic lift are weak as well. The upslope forcing is
decent and this should help initiate showers from along the Blue
Ridge north and west across the mountains. Precip chances taper off
to the east and south where moisture and forcing diminish. There may
also be a few thunderstorms each afternoon as weak instability does
develop. QPF is generally light through the period, but some
moderate amounts are possible across the southwestern mountains
Wednesday morning. Highs and lows remain very warm with near record
high temps and lows near record high minimums with readings above
normal high temps.

The complicating factor in this forecast is the afore mentioned cold
front. Guidance agrees that the northern portion of the front will
sag south toward the area in backdoor fashion. However, they don`t
agree on how far south it moves. The GFS and NAM suggest the front
moves into the NW piedmont and northern foothills. However, the
ECMWF and the Canadian show it stalling somewhere near the VA/NC
border. The models are consistent with themselves from run to run
but the dichotomy between solutions remains. Have retained some
features of a backdoor front but don`t mainly show a glancing blow
across the NW Piedmont.


As of 120 AM EST Tuesday: Starting Friday morning, expecting surface
high pressure over Maine ridging down the East Coast and pushing a
backdoor cold front to perhaps halfway across NC. The I-77 corridor
could be affected briefly before the high moves out over the
Atlantic and this front retreats north as a warm front into
Saturday. A mostly stationary front extends from the Ohio Valley to
Texas on Friday.

The 500mb pattern has a high centered east of the Bahamas with SW
flow pumping moisture from the Gulf to across the SE States Friday
into the weekend. The deep 500mb trough over the West on Friday
begins to move east over the weekend. The Bermuda / Bahamas High
will be moving east or suppressed south as ridge breaks down with
this western trough moving toward the East Coast. Moisture gets
deeper progressively but of course best along the front which will
progress east from the Mississippi Valley Saturday. 850mb flow on
both the GFS and EC has SW wind of 40 to 50 kts Saturday night
crossing our area. POPs increase on Sunday as the front crosses our
area. Instability rather low Sunday afternoon with CAPE values over
the Carolina Piedmont around 200 or less. Shortwave energy crosses
the Great Lakes Sunday with the frontal precip fading as it crosses
the Carolinas. The GFS is a bit faster in taking the front through
and EC a bit slower but each have the front out of our area by
Monday morning. The front stalls out early next week from the
northern Gulf Coast to northern Florida. General drying but there is
some potential waves passing along this frontal boundary could
affect at least southern portions of our forecast area in the first
half of next week.

Temps over ten degrees above normal until front passes then closer
to normal early next week. Max temps a little cooler on Friday for
the NC areas north of CLT due to the backdoor cold front.


At KCLT and elsewhere: With the exception of KAVL currently at VFR,
expect MVFR to persist across the TAFs through tonight, with
increasing clouds, areas of fog and -RA/-DZ allowing for
widespread MVFR/IFR/potential LIFR overnight into Wednesday

Latest satellite imagery continues to depict cloud cover eroding
(mainly along the TN border) as the warm front to the south
continues to slowly push northward with a gradually eroding insitu
wedge. With VFR currently at AVL and the potential for VFR at KHKY
as well before sunset today, overall expect persistent stratus to
allow for MVFR/IFR due to cigs to persist through tonight. SSW winds
AOB 10 kts will persist through the evening hours, with downslope
winds creating gusts near 20 kts expected to subside tonight.
Overnight, as light southerly winds persist, increasing chances for
-RA/-DZ along with increasing cloud cover and areas of fog, expect
MVFR/IFR/LIFR to become widespread overnight into early Wednesday
morning and continue into the early afternoon hours. Anticipate any
dense fog that develops to not be as widespread as seen this

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       High  89%     High  82%     High  84%     High  86%
KGSP       High  82%     High  83%     High  93%     High  91%
KAVL       High  87%     High  87%     High  85%     High  89%
KHKY       High  89%     Med   63%     High  85%     High  93%
KGMU       Med   78%     Med   79%     High  91%     High  95%
KAND       High  86%     High  81%     High  96%     High  88%

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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