Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201443

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
943 AM EST Mon Feb 20 2017

Warm high pressure will move over the area through the early part of
the week, bringing temperatures close to record highs. A cold front
will bring a chance for some modest rainfall over the area by mid
week, followed by brief drying, before a frontal system arrives next
weekend with rain and thunder chances.


As of 930 AM EST...A very pleasant day on tap for the area, as
surface high pressure noses down from the eastern Great Lakes under
an approaching sharp upper ridge axis. Temps got off to a cool
start, but still think the current max temps look on track, given
the nearly full sun and strong subsidence inversion expected today.
Little change needed to the forecast with this update.

Otherwise, a strong upper level ridge has developed to the west of
the FA and streaks of thin Ci are rounding axis and dissipating in
the downstream subs zone. Expect this Ci to increase in coverage
slowly this afternoon...and become more overcast thru the overnight
period. Soundings are showing a pronounced subs inversion lowering
to h9 today and winds weakening sigfnt/ly thru 12 Kft. Meanwhile a
cP sfc high will ridge in from the NE...however no lowering sfc temp
adv will occur according to llvl sigma winds. So...will count on
very good insol and compressional warming to allow max temps to
reach about 20 degrees above normal. This will likely reach or break
the record of 75 F at GSP by a degree or two. CLT and AVL will also
come close to record highs for this date. The increasing cloud cover
overnight will aide in holding mins about 10 degrees above normal.
Basically...another very nice Feb day is in store feeling more like
late Apr.


As of 2 AM EST Monday: The dominant ridge over the southeast will
move off the eastern seaboard Tuesday as the southern stream closed
low pressure system wobbles near the Louisiana Gulf coast and
northern stream waves create more zonal flow across the western
Carolinas. Low level southerly winds developing ahead of the Gulf
coast system may provide some afternoon upslope triggering for
isolated showers in and near the southern Appalachians Tuesday
afternoon. Deeper moisture between the northern tier frontal system
and the Gulf coast low will then likely pool over the region Tuesday
night to warrant briefly enhanced PoPs for rain showers throughout.
Temperatures will exhibit the smallest diurnal range of the week
Tuesday-Tuesday night given the increased clouds and precip chances,
but with Tuesday afternoon maxes still reaching around 70 in some
lower piedmont areas.

The closed system over the Gulf of Mexico should continue to move
southeast toward the FL Keys Wednesday through Wednesday night. 850
mb flow over the southeast is expected to become more westerly with
time, with deeper moisture likely moving off to the east. This will
allow PoPs to steadily dwindle across our forecast area with mainly
continued shower chances over the mountains by Wednesday night.
Wednesday afternoon maxes should rebound to some 15 degrees above


As of 230 AM EST Monday: The medium range picks up at 12Z Thursday
morning with rising heights aloft, indicating the potential is there
once again for near record highs across much of the area. Later on
Thursday, guidance is showing some signs of possible warm front
development near the southern Appalachians as the surface low
ejecting from the Southern Plains undergoes rapid surface
cyclogenesis over the Midwest. With our area under the influence of
moist southerly flow at the surface and weak low level Q-vector
convergence, some QPF response Thursday later in the afternoon looks
favorable. Though not the most favorable setup as far as dynamics or
instability , we will likely have the opportunity for a small amount
of destabilization Thursday afternoon and evening, so thunder
remains on the table as a possibility Thursday evening. Temperatures
will be at least 20 degrees above average Thursday and Friday.

By Friday, the surface cyclone will have lifted towards the NE after
deepening considerably as its progressive cold front crosses over
the southern Appalachians. Upper support for this system on Friday
is more substantial with an upper trough positioned just to the
north of our area. Though it is clear that the best instability and
dynamics are well to our north with this cyclone in the OH river
Valley, right now it appears that CAPE and most shear/SRH values are
non-zero on Friday. The best forcing will arrive Friday night and
early Saturday morning, basically at an unfavorable time for dirunal
heating to contribute too much to instability. The pattern for
Thursday through Friday remains interesting even if not overly
threatening, and will be watched as this time period comes into
better range of higher-resolution models.

The forecast becomes quite easy by the time the front has the
cleared the area on Saturday, with dry high pressure building in at
the surface and briefly in in the upper levels. A longwave trough
approached by the end of the medium range, indicating a possible
return to cooler weather, though this "cool down" will only drop
temperatures to about 10 degrees above average.


At KCLT and elsewhere: Mainly VFR conds thru the period at all sites
except for some MVFR CIGS/VSBY at KAVL and KHKY arnd daybreak due to
increasing llvl Atl moist flux. Other than that...increasing Ci and
winds remaining weak with a strong ridge axis traversing the area
and a broad sfc high building in from the NE.

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 remain highly uncertain from mid week on.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High 100%     High 100%     High 100%     High  87%
KGSP       High 100%     High 100%     High 100%     High  93%
KAVL       High 100%     High 100%     High 100%     High  95%
KHKY       High 100%     High 100%     High 100%     High  83%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     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      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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