Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 180852 AAD

Area Forecast Discussion...UPDATED
National Weather Service Greenville-Spartanburg SC
352 AM EST Wed Jan 18 2017

A weak cold front will cross the Carolinas from the west today
bringing increased chances for precipitation. A warm front will lift
northward over the region on Thursday and Friday, bringing more rain
to the southeast. A more significant low pressure system is expected
to develop over the region on Sunday, bringing more unsettled
weather to the area.


A cold front is currently draped from northern Alabama through the
southern Appalachians and moving steadily SE. A potent short wave
trough, shown rather prominently in the latest water vapor imagery
over Indiana/Ohio will continue to dig E/SE through the morning, and
should exit the Mid-Atlantic this afternoon. Surface high pressure
spreading into the TN Valley in the wake of this feature will push
the cold front south of the area by the end of the day. However,
with the front taking on an increasingly zonal orientation, and
predominant W/NW low level flow expected across the region, the
frontal circulation will continue to weaken, and nothing more than
token small chance pops (mainly across the mtns and southern
Piedmont) appear warranted this morning.

Today`s main highlight will be warm temps east of the mtns,
esp along and south of the I-85 corridor, where the front is
unlikely to completely clear the area until this afternoon, while
strong compressional/downslope warming will offset the relatively
weak cold air advection in areas that do see fropa earlier in the
day. Maxes are expected to range from 10-15 degrees above climo
(i.e., mid 60s) across the northern Piedmont and foothills, as well
as the mtn valleys, to as much as 20 degrees above normal across the
SC foothills and Piedmont, where temps in the 70s appear to be a
good bet. Record highs will be flirted with at KGSP and KCLT.

The front should be south of the forecast area by this evening, and
lowering thickness values, while a weakening gradient and initially
clear skies will yield decent radiational cooling conditions, at
least prior to the anticipated arrival of high clouds towards
daybreak. This will allow for min temps that will be as much as 20
degrees cooler than Wednesday morning`s readings, but still 5-10
degrees above climo.


As of 300 AM EST Wednesday...The short range begins with an h5 ridge
axis overhead and a relatively warm sfc high encompassing the
Carolinas. This ridge and high will migrate to the Atl coast thru
the day while moisture flux and layered clouds increase from the
west. An occluded frontal zone will work it/s way into the CWFA
overnight bringing -shra to most areas by daybreak. Meanwhile...the
precip will interact with the prevailing sfc ridging and produce a
hybrid-wedge with a distinct bndry generally bisecting the I-85

Model soundings show high 0-3 km helicity along this zone...arnd 300
m2/s2...and a developing strong h85 jet aligned within WAA btw 06z
and 15z. Instability shud remain quite low with the NAM only showing
about 150 J/kg peaking arnd 12z and the GFS remaining stable. Also
there will be a nice slug of h7-h5 dpva crossing during this
time-frame. So...there will be sigfnt elements in play for strong
semi-organized and possibly rotating line segments through the
morning hrs along and south of I-85. Too much uncertainty is had
with instability for inclusion of thunder in the grids and the time
of day is a neg factor for a mention in today/s HWO...but this
situation will be watched closely over the next couple days. Max
temps wlll generally remain arnd 10 degrees above normal even with
increasing clouds as llvl WAA mixes into the bndry layer.


of 350 AM EST Wednesday: The ext range remains pretty interesting
with the expected synoptic pattern. On Sat...the recently dominant
subtrop high will get nudged east as Fri/s elongated h5 trof swings
toward the Midwest and increases the overall broadness of the wrn
CONUS trof. Meanwhile...strong energy originating from the Pac NW
will have made it across the srn Rockies and will instigate quick
cyclogenesis across the TX/OK panhandle region. This system will
become occluded quickly as well...and will serve to deepen and
strengthen the overall parent l/w trof as it moves into the deep
south through Sun.

With the subtrop ridge breaking down Sat...a llvl bndry across the
nrn GOM will moisten up sigfnt/ly and begin to interact with the
incoming occluded system while advancing toward the CWFA as a warm
front. Not expecting much precip during the day Sat with generally
mech lift -shra across the mtn zones spreading east...but by Sat
night ulvl difl increases along with steepening mlvl lapse rates.
Good moist GOM flux will ensue as well increasing the moderate to
heavy rain potential...with mod/high rainfall amounts likely
continuing thru Sun night as the occluded front crosses the FA. The
normally stingy with instability GFS has increasing SBCAPE values
beginning aft midnight Sat...reaching near 750 J/kg by mid-day Sun.
The soundings are also showing high amounts of llvl helicity as the
warm front bndry crosses the area. Thus...the period Sat night thru
Sun night will have the potential for convective heavy precip along
with stg/svr tstms. Will keep the current wordage in the HWO.

On Mon...the upper low crosses the area and will maintain isol/sct
-shra/tstms...with rather light additional rain amounts expected.
Some below freezing air does make it to the higher mtn peaks Mon
night and enough lift and moisture shud be available for periods of
light snow with little or no accums. A relatively warm srn stream
high builds in Tues and generally temps over the ext range will
remain arnd 10 degrees above normal with no sigfnt cP airmass


At KCLT and Elsewhere: Some rather radical changes have been made to
the TAF suite, as observational trends lend little support to the
development of visby or even cig restrictions this morning. This is
due to a 5-10 kt surface wind, which should continue at the Piedmont
and foothills terminals through the morning. (Meanwhile, a NW wind
of around 10 kts will develop at KAVL by around 09Z as a cold front
passes through the area). These winds are expected to maintain the
current 5-10 degree temp/ dewp spread, which won`t be enough to
support fog development at the main TAF sites. Additionally, a
strong westerly downslope flow is developing in the 020-050 layer,
and this will likely prohibit much in the way of sub-VFR cloud
development. Statistical guidance is quickly coming around to this
thinking as well, favoring a much more optimistic forecast than the
current one. Therefore, we have removed all restrictions from the
TAFs for this forecast period. The only exception is at KAND, which
is less impacted by downslope effects in westerly flow, but even
they only see a tempo for MVFR cigs around daybreak.

Otherwise, frontal boundary will cross the area this morning with
shower chances being confined to the mtns, but probabilities only
warrant a VCSH even at KAVL. Winds will turn to the W/NW at around
10 kts at all Piedmont 12Z and 15Z. VFR clouds will clear out by
late morning, with SKC conditions expected through much of the
daylight hours.

Outlook: Surface low pressure approaching from the southwest will
bring chances for widespread precip to the area Thursday and Friday.
Yet another cold front will bring chances of precip and restrictions
on Sunday.

Confidence Table...

            09-15Z        15-21Z        21-03Z        03-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  95%     High  96%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High  86%     High 100%     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 1933     20 1977     57 1943      0 1994
   KCLT      71 1937     23 1893     62 1943     10 2003
   KGSP      71 1928     30 1977     60 1943      5 1893


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      70 1974     21 1940     53 1907     -5 1994
   KCLT      69 1929     24 1994     54 1907      6 1994
   KGSP      72 1974     25 1994     54 1937      5 1994


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      69 1906     24 2009     53 1954    -13 1985
   KCLT      71 1951     30 1983     53 1890     -2 1985
                1929        1893
   KGSP      72 1933     30 1983     56 1922      1 1985


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      72 1927      8 1985     59 1927    -16 1985
   KCLT      73 1935     24 1985     58 1954     -5 1985
   KGSP      73 1927     26 1985     59 1933     -4 1985


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      73 1932     21 1960     59 1933      0 1970
   KCLT      74 1937     29 1970     60 1906      5 1970
   KGSP      72 1938     31 1970     58 1933      3 1893


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      73 1927     20 2005     54 1999      1 1936
   KCLT      75 1927     27 1970     59 1999      9 2003
   KGSP      73 1974     30 1970     58 1999      5 1893


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      74 1949     18 1963     54 1950     -7 1963
   KCLT      74 1967     26 1948     54 1909      7 1963
   KGSP      76 1967     26 1948     59 1974      9 2014




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