Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 231916

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
216 PM EST Fri Feb 23 2018

Very warm conditions will continue through most of the weekend. A
cold front will slowly cross the area Sunday into Monday, bringing
greater chances of showers and a few thunderstorms with it. Drier
and cooler high pressure will settle over the region Tuesday through


As of 200 PM EST Friday:  Nothing like a nice spring
February!  Modest heating this afternoon is underway with CLT/GSP
already tying records, likely to break them.  As for KAVL, still
a few degrees short, but still time for warming to overcome those
records as well.  Anyways, overall the pattern hasn`t changed all
that much with a large upper anticyclone centered over the western
Atl keeping a stalled frontal axis to the west.  With that, said
above normal temperatures will prevail today/tonight, less likely
tomorrow as the records are a few degrees warmer.  Otherwise,
expecting partly cloudy skies this afternoon as ample llv moisture
and heating combine to yield cu, with some sct`ing favored into
the evening/overnight.  Another round of lower stratus and possibly
fog is expected again tomorrow morning given a persistence fcst,
therefore sky cover is favored to increase toward sunrise Saturday,
eventually sct`ing out once again into the afternoon yielding
above normal temperatures.  As for precipitation this fcst cycle,
did continue with increasing slight/chance pops along the high
terrain this evening/overnight as guidance favors a wave of energy
sliding along the stalled front, albeit with some slight timing
differences.  Beyond that, heating into the afternoon hours on
Saturday could yield enough free sbcape along the TN line given
furthest distance from the aforementioned Atl ridge, thus iso/sct
tsra cannot be ruled out.


As of 100 PM EST Friday: At the start of the short term period
Saturday evening, the strong upper ridge will still be in place over
the western Atlantic, with a deep upper trough building over the
Rockies. The initial shortwave embedded within the trough will be
approaching the MS Valley at the start of the period, with a
secondary shortwave diving into the northern Rockies. Surface highs
in eastern Canada and over the western Atlantic will be separated by
the quasistationary warm front, while a cold front will drag across
the Lower MS Valley as the surface low over the Mid MS Valley
continues to occlude. Showery activity can be expected Saturday
night especially across typical upslope areas as low level WAA
continues. The cold front will push east on Sunday, losing some of
its oomph, as the upper ridge is forced south and will begin to
retrograde into the Gulf and western Caribbean. With the area
remaining in the warm sector, the synoptic lift (though weakening)
added by the front will likely be enough for at least a few
thunderstorms to develop across the Piedmont and maybe foothills,
with better chances across the Upstate and NE GA. SBCAPE is not
particularly impressive, remaining below 500 J/kg, with deep-layer
shear increasing (50-60kt) as the front approaches. Certainly some
minimal concern for HSLC convection Sunday afternoon, so will
continue to watch forecast evolution. Expect one more day of
afternoon highs 15+ degrees above seasonal normals.

Still seeing some differences in how the ECMWF and GFS are handling
the secondary surge of moisture on Monday, but the 12z ECMWF has
come in slightly farther SE with the QPF axis, closer to what the
GFS has been indicating. Basically that secondary shortwave will
push into the Plains and pull another slug of moisture out of the
Gulf as the upper wave begins to damp. The cold front will stall
across the area and may briefly lift back north with the surge of
moisture, but it`s starting to look like the more significant
rainfall is less likely (and even if so, it would be farther S) with
the surface low working it`s way more across the fall line rather
than I-85. Should see highs on Monday a good 5-8 degrees cooler (but
still 10 or so degrees above normal) than on Sunday, but this will
be highly dependent on how quickly the front moves through. All pops
should be pretty much out of the area by 00z Tuesday.


As of 130 PM EST Friday: Dry high pressure will build in on Tuesday
in the wake of the frontal passage, with highs still above seasonal
normals but at least trending in the right direction. A broad low-
amplitude ridge will build across the Southeast, while a cutoff
midlevel low forms over CA. Split flow pattern will come together
over the Northern Plains, and as the cutoff low slowly moves east,
surface low formation over the central Plains will begin to drag
another slug of moisture out of the Gulf and into the Lower MS
Valley. Our surface high will move off the NC/VA coasts by Tuesday
night, with the moisture advection really picking up shortly
thereafter. Expect some showery activity to begin Tuesday night
across the typical upslope areas, spreading east and north Wednesday
as the warm front surges; however, indications are that the
precipitation into the dry surface layer may result in some insitu
damming Wednesday, which will stall the warm frontal surge into the
Carolinas and keep highs Wednesday pretty close to seasonal normals.
GFS is quite a bit stronger with the development of the surface low,
and also a bit faster, but enough similarities in the general trend
to lend some confidence to precip pushing out on Thursday night.
Damming will erode (per current guidance) on Thursday leaving our
area again in the warm sector and highs Thu about 10 degrees above
normal. Lingering NW flow showers can be expected across the
mountains with the upper system, and behind the front (whenever it
ends up passing) we might actually get some CAA to work with, but
too far out to get into details at this time.


At KCLT and elsewhere: A moist pattern continues across the region
this fcst cycle as a stalled front remains westward keeping the
fcst area in the warm sector.  With that, moist swly/sly flow
will prevail through the period with said moisture supportive of
varying cig heights.  With that, initialized MVFR at KAND/KHKY
given lingering stratus, while leading off with low VFR at all
other sites.  All sites should go VFR within the next hour/two.
Otherwise,  brief relief from the low cigs/visb into the overnight
before another round of said restrictions returns ahead of
sunrise Saturday.  Meanwhile, a weak wave looks to traverse
the aforementioned frontal boundary, sliding into the TN valley
overnight.  Thus, cannot rule out some stray showers across the
western tier of the fcst area to affect all sites aside for KCLT,
therefore prob30s were included.  Conditions will improve from
MVFR/IFR and possibly LIFR cigs and visb into the late morning
hours as has happened today, thus each site will experience
improvement late.  As stated, winds will remain swly/sly through the
period with some low end gusting possible at KAVL this afternoon.
Otherwise look for winds in the 6-10kts range at all sites this
afternoon, weakening overnight with loss of mixing, increasing
again on Saturday.

Outlook: Moist conditions will keep chances for restrictions
elevated through the period, with the best chances for low cigs/visb
to occur each morning.  Precipitation chances are also slightly
elevated, mainly across the high terrain.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High 100%     High 100%     High  92%     High  83%
KGSP       High  98%     High 100%     High  89%     High  89%
KAVL       High 100%     High  98%     High  82%     High  86%
KHKY       High  92%     High 100%     High  85%     High  89%
KGMU       High 100%     High 100%     High  86%     High  91%
KAND       High 100%     High 100%     High  87%     High  84%

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      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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