Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 222147

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
447 PM EST Thu Feb 22 2018

Warm and moist conditions will continue through the weekend until a
cold front moves into the region on Sunday. Showers will persist
Sunday into Monday before dry high pressure builds in on Tuesday.


As of 430 PM: A rather stagnant pattern continues to prevail
across the eastern half of the CONUS as strong subtropical
ridging dominates over the western Atlantic, with troffing
out west.  At the surface, the primary feature continues to be
a quasi-stationary frontal axis draped along the OH and mid MS
valleys, which continues to promote modest QPF for those areas.
Closer to home, sly flow around the parent surface high consequent
of the upper anticyclone mentioned above is promoting sustained
warm/moist advection across the southeast states. Record highs
were broken at all three climate sites (GSP/CLT/AVL) again today;
the model that captured the warm temps the best was the RAP and
that was used to update hrly trends into the early evening.

Moving on into the evening/overnight hours, decoupling should
allow for increasing low stratus yet again tonight, generally
leading to a repeat of last nights conditions. Updated sky cover
to in favor of the slightly clearer NationalBlend guidance,
which worked out pretty well last night. We do favor a bit lower
visibilities in association with any fog tonight given slightly
improved decoupling.  This low stratus will lift into the mid/late
morning hours with partly cloudy skies prevailing by period`s end.
As for pops, did continue with a low end slight chance pops along
the southern escarpment accounting for any sly/swly upsloping, but
with this update trimmed back values close to the TN border this
aftn/evening in light of convective trends in East TN. Also we have
included slight chances along/north of I-40 beginning in the morning
where the NAM continues to hint at an approaching back door front.
On that, confidence is low as the NAM remains really the only source
favoring such.  Otherwise, expecting another round of record high
min temps Friday morning, and record highs into the afternoon.


As of 200 PM EST Thursday: The persistent upper ridge will remain in
place over the western Atlantic with corresponding surface high
allowing low-level WAA to continue across the Southeast. As we start
the period on Friday night, a sharp shortwave pushing across the
Rockies will begin to lift into the Plains, while a warm front
remains in place from TX to the OH Valley. This will result in a
continued focus of prolonged excessive rain across that area.
Impacts to our area will be pretty minimal, but continue upslope
flow toward the mountains will allow for intermittent showery
conditions to continue, with an uptick starting Saturday afternoon.
With the warm and humid conditions, there may be enough surface
instability to get a few thunderstorms especially across southern
zones, but nothing too significant. The bigger story will be the
continued ridiculously warm temperatures, with lows remaining closer
to seasonal highs, and highs 15-20 degrees above normal, both around
record territory. This will continue on Sunday, but could see highs
Sunday just a couple of degrees cooler with increased cloud cover
(see below).

During the day Saturday, another shortwave will dive down the NW flow
behind the Plains wave into the Rockies, acting to finally kick the
systems east. The upper ridge will be forced SW and will continue to
slowly retrograde as we push into the extended. However, for Sunday,
the cold front will stretch across our area and elongate as it
stalls, while that secondary shortwave pulls another slug of
moisture out of the Gulf and toward the Southern Appalachians,
keeping pops in the area through at least Monday morning, though the
ECMWF is a little slower with the final kick and doesn`t move pops
out until Monday evening. Where the front ends up across the area
Sunday into Monday will of course significantly impact temperatures
and confidence is low, but for now given the pattern figured it`s
better to err on the warm side so generally trended toward the
slower ECMWF. Even so, Monday highs will be much more reasonable
(still above normal), with improvement expected into the extended as
the front finally scours the airmass out.


As of 230 PM EST Thursday: Behind the front Monday night into
Tuesday, conditions look much more seasonable (still slightly above
normal temperatures) and overall pleasant with dry high pressure
dominating the area into Tuesday night. The upper ridge will be over
the western Caribbean by this point, but a deepening trough across
the Desert SW (cutoff low on the ECMWF but sharp/deep trough on GFS)
will start raising some ruckus for the end of the period. Another
round of moisture will lift toward the area during the day on
Wednesday as, once again, low-level WAA increases around the western
periphery of the surface high that will be centered just off the
NC/VA coast. Differences in the operational models become more
unsurprisingly more significant toward the end of the period, but
generally still looks like moisture will be lingering with
temperatures remaining above normal.


At KCLT and elsewhere:  MVFR trending to VFR through the afternoon
as persistent low/mid stratus continues to gradually erode across
portions of the NC/SC piedmont to affect all sites except KAVL where
mid/high clouds will highlight the skies, if not skc.  Otherwise,
moisture advection will continue across the region through the
day/night with flow remaining veered.  With that, guidance once
again favors lowering of cigs/visb into the MVFR/IFR/LIFR range
ahead of sunrise on Friday.  Did keep the fcst a bit optimistic at
this point thus not including any LIFR, but did favor IFR at all
sites.  Recovery is expected to be slow yet again on Friday morning
thus held any improving cigs to MVFR levels at most.  Winds on
Friday will remain sly in the 6-10kts range.

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, especially during the late night
and morning hours.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High  90%     High  92%     Med   61%     High  93%
KGSP       High  94%     High  92%     Low   55%     High  82%
KAVL       High 100%     High  92%     Med   68%     Med   79%
KHKY       High  89%     Med   79%     Med   77%     High  87%
KGMU       High  90%     High  92%     Low   51%     Med   78%
KAND       High  98%     High 100%     Low   46%     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      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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