Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
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 240529

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1229 AM EST Fri Feb 24 2017

A cold front will move through the area tonight with showers and
thunderstorms mainly for the mountains. Temperatures cool to near
normal late in the weekend then warm up again early in the week.
Another stronger cold front will move through the area mid week,
increasing rain chances again.


As of 1220 AM EST Friday:  Updated discussion for taf issuance.
Starting to see stratus development across portions of the NC
Fthills as expected, with further southward expansion favored
through daybreak.  Visbs will also be reduced by patchy fog, but
given the low ceiling stratus, think chances for dense fog are low
with the exception of the mtn valleys as well as for locales east of
I77 where less stratus is expected.  Otherwise, the fcst remain on
track with only minor t/td adjustments needed/made with this update.

Previous Discussion: Low stratus is expected to move in during the
predawn hours, while some fog may develop and produce appreciable
vsby restrictions (particularly if the stratus does not arrive as
early as anticipated). Other than a few sprinkles near the Blue
Ridge, the fcst remains dry through morning. Mins will remain a
remarkable 15 to 20 degrees above normal.

As heights fall to our west with the eastward movement of
the Mississippi Valley low, low level winds pick up and veer
slightly, providing slightly better upsloping. By late afternoon
this may generate some very light precip along the southern-facing
Escarpment, but only a low slight-chance PoP is warranted. Inversion
looks much too strong for any chance of thunder at that time, so
that mention has been removed from the fcst. Temperatures should
trend upward from today, reaching the upper 70s over much of the
Piedmont, and low 70s even in the mountain valleys. The current
fcst is within a couple degrees of the records at GSP and Charlotte,
but well shy at Asheville.


As of 2pm Thursday:  Friday evening, upper long wave/surface cold
front will be approaching the area from the west, with front
reaching TN/NC stateline early Saturday morning, and passing through
the CWA by noon on Saturday.  Airmass is strongly capped ahead of
the front.  Cap erodes with FROPA, though BUFKIT soundings indicate
only marginal instability will be present, as front passes through
at a diurnally unfavorable time for CAPE.  Line of possibly severe
storms will be approaching with the front, but latest NAM/GFS both
deamplify line dramatically as it crosses the mountains. It is
possible some severe winds will persist for awhile as line moves
into the mountains and the CWA Saturday morning, but storms should
break-up as they move much further east. With 850mb winds of 30kts
ahead of the surface trough, Winds will increase with the FROPA,
especially over the higher terrain, though they should remain below
any advisory need. Dewpoints plummet behind the front with dry/cool
advection, which will further limit shower potential, with activity
mostly completed by noon on Saturday.

There is some potential for very light snow over the higher mountain
elevations Saturday evening with some upslope enhancement and cold
air, but this will be very limited due to very dry airmass.

Surface high pressure will build-in behind the front with clear
skies and light winds on Sunday.  Sunday morning is the cold spot in
the forecast with clear skies/light winds/ and dry air all
contributing to below freezing temperatures over western North
Carolina and northeast Georgia, with low to mid 30s and possible
frost in Piedmont areas. High moves east of the area Sunday evening,
with some southwesterly surface flow developing, that will begin the
process of increasing moisture again.


As of 215 PM EST looks like the middle part of next
week will be fairly active across the region. By the time high
pressure moves off the east coast Sunday night, the next system
should already be organizing to our west. The first issue has to do
with the arrival of moisture and forcing on Monday, and the new
ECMWF does not clear any of that up. In fact, the trend is opposite,
with the GFS being a bit faster while the ECMWF is slower as it
delays the arrival of moisture and precip until late Monday. The new
guidance at least gives some better confidence that rain will not
develop until after sunrise on Monday, so the fcst reflects that
thinking with a dry Sunday night. The fcst trends more GFS-like for
Monday with a chance of showers developing from W to E by late in
the day. From that point onward, although the details are different,
the guidance suggests a similar conclusion, that being a boundary
laying down across the area late Monday through at least Tuesday.
Low level moisture and isentropic upglide suggest at least a chance
of precip across the entire region through Monday night and Tuesday.
The location of the boundary might be problematic for temps. If it
sets up to the south, it may become the edge of an in-situ cold air
damming wedge on Monday that persists into Tuesday, in which case
the high temp fcst of well above normal values is called into
question. Will not depart significantly from the consensus...yet.
Will the boundary wash out Tuesday night as in the ECMWF or will it
remain active through Wednesday as in the GFS? Through the middle
part of the week, the passage of two short waves to the north may
bring two low level jet surges across the region, but the timing is
uncertain, as is the degree of instability.  However, now that the
atmosphere thinks it is April, we have to be on the lookout for
severe weather, and it seems like in this pattern we will get some
sort of overlap between higher shear and low CAPE at some point
between Monday and Wednesday night. The front should move across the
region early Thursday to bring an end to most problems. There could
be some NW flow precip early Thursday, with a changeover to snow
showers at the high elevations along the TN border, before the
moisture pulls out. The passage of the front should knock our temps
back on the order of ten degrees.


At KCLT and Elsewhere:  VFR/MVFR and IFR conditions expected
through this taf cycle at all sites.  Moisture advecting in from
the Atlantic this morning will settle across the region, leading
to low stratus development toward daybreak.  Guidance favors
MVFR/IFR cigs at all sites, with visbs likely to remain in the
4-5sm range for those sites affected most by the low stratus,
with the exception of the fog prone mtn valleys to affect KAVL.
Therefore all tafs feature restrictions through daybreak, with
improvement expected into late morning before skies sct to low/mid
VFR beneath high cirrus.  Winds look to remain light sly through
morning, increasing/veering swly into the afternoon as a frontal
complex approaches from the west, which will lead to precip and
restrictions within the next taf cycle.

Outlook:  A cold front will move through the area on Saturday
leading to increased shra/tsra chances, with restrictions expected
as well.  Drier air will advect in behind the front as high pressure
builds from the west, likely keeping chances for restrictions
lower for Sunday, before another wave approaches on Monday once
again increasing chances for precipitation/restrictions.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High  94%     High  89%     High 100%     High 100%
KAVL       Med   75%     High 100%     High 100%     High 100%
KHKY       High  81%     Med   66%     High 100%     High 100%
KGMU       High 100%     Med   72%     High 100%     High 100%
KAND       High 100%     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      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




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