Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 190611

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
111 AM EST Sun Feb 19 2017

A weak upper low moves east across the Carolinas tonight then off
the Carolina coast Sunday. A strong upper ridge moves in to start
the week, with much above normal temperatures. Another period of
light rainfall is possible mid week as a weak upper trough moves
through the region. A cold front approaches at the end of the week
with possible showers and thunderstorms.


As of 1245 AM EST: The phasing upper trough is crossing the
Appalachians early this morning. Associated deformation zone forcing
around the low circulation is sliding southeast from Kentucky and
central Tennessee back toward the NC/TN line, but precipitation
coverage is not particularly robust in this region. Will keep mainly
lower end slight chance to chance PoPs going in the NC mountains
near the TN line through the morning hours before conditions dry
this afternoon. Otherwise, a full latitude ridge will build east
from the central CONUS this afternoon through tonight. With
downsloping and scattered clouds permitting decent insolation today,
will feature max temperatures a couple of degrees above guidance but
likely just below record highs. Surface high pressure building into
the region tonight will permit fairly good radiating conditions and
plenty of 30s mins in the lower and 40 to 45 east, but well above


As of 2pm EST Saturday: By Sunday evening, southeast CONUS upper
shortwave will be well east of the area and a transitory upper ridge
will be moving in, with dry downslope northerly flow and clearing
skies.  This ridge will keep things dry and mostly clear on Monday,
with clouds increasing prior to the next frontal/upper wave system
due in Tuesday evening, with a chance from some showers in the
mountains as early as Tuesday evening.  Temperatures will be 10 to
15 degrees above normal Monday and Tuesday.  Winds will continue to
be northerly to northwesterly at 5 to 10 kts early on Monday,
veering to easterly and weakening as center of surface high settles
over the region Monday evening, and then picking-up from the
southwest on Tuesday in advance of the next trough.


As of 230 PM EST Saturday:  The medium range fcst period initializes
on Tuesday evening amidst weakening east coast ridging by way
of a progressive northern stream trough, while a close southern
stream upper cyclone moves out of the Rio Grande Valley into the
central Gulf of Mexico.  At the surface, the primary features of
note will be a broad anticyclone along the east coast and a cold
front extending across the Great Lakes region into the OH Valley.
Synoptic pattern evolution moving through the period will be
highlighted by total breakdown of the amplified east coast
upper ridge leading to migration of the elongated surface high
southward near Bermuda.  The aforementioned cold front looks to
stall across the OH Valley, possibly making it as far east as
the Central Appalachians, however not likely intruding into the
Southern Appalachians thanks to the repositioned surface ridge.
Meanwhile, guidance seems to have converged on some details
regarding the closed H5 cyclone moving through the Gulf, which
now looks a bit weaker, strongest in the ECMWF, with good track
agreement to the southeast toward southern FL.  Thus, little
if any impacts are expected across Northeast GA and the Western
Carolinas.  That said, weak moist upglide atop the offshore high
will at least warrant low end pops both Wednesday and Thursday.
Moving along, as the southern stream H5 low moves out of the
picture, a few days of southerly flow are expected across the
southeast states thanks to the Bermuda high, while a west coast
system gains strength and plows through the plains into the MS
River Valley by Friday.  Surface cyclogenesis beneath a modestly
deep upper low looks to yield a rather strong/progressive surface
cold front that will march across central CONUS and into the
Appalachian region either on Friday evening, possibly sometime
on Saturday.  Timing inconsistencies within the op guidance lead
to much uncertainty regarding the details, nevertheless, expecting
a strong and potentially convectively active fropa next weekend.
Behind said front, broad Canadian high pressure looks to dive
southward into the Plains by yielding drier yet cooler conditions
to round out the weekend.   Temperatures are expected to remain
well above normal, cooling to near normal at periods end.


At KCLT and elsewhere: Lingering lower level moisture under the
passing upper low are producing spotty MVFR cigs around the region.
The current thinking is that the lower cloud deck will be scattered
overnight as slightly drier air works in everywhere but the western
mountains. Will also feature MVFR fog developing at KAVL and KAND,
with slightly lesser chances at the other foothill/piedmont sites.
Winds will remain NW through the period at KAVL, while SW winds at
the foothill/piedmont sites early will become northwesterly after
14Z. VFR level stratocumulus and passing higher clouds should be
mainly scattered through the rest of the day before clearing

Outlook: Expect VFR conditions to continue through early in the week
before another low pressure system gradually brings moisture back to
the area from Tuesday through late week. Precipitation and
associated restrictions, however, remain highly uncertain.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High  97%     High  94%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       Med   70%     Med   74%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High  90%     High  94%     High 100%     High 100%

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 2014     16 2015     54 1951      3 2015
   KCLT      76 2014     26 2015     55 1961      8 1958
   KGSP      75 2014     30 2015     55 1961      9 1958
                1916        1900                    1900


  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




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