Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 181930

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
230 PM EST Wed Jan 18 2017

A warm front will lift northward over the region on Thursday and
Friday bringing more rain to the area, particularly on Thursday
night. A more significant low pressure system is expected to track
across the region this weekend, bringing rain and thunderstorms for
Saturday, Sunday, and Monday. High pressure will build into the
region for the middle of next week.


As of 200 PM EST Wednesday: What cold front? Yeah...a cold front
pushed through today and at AFD time had exited the forecast area as
evidenced by the wind shift and much drier dewpoints advecting in
(especially in the mountains), but you certainly wouldn`t know it
from temperatures! Thicknesses from the dominant upper ridge and
more specifically strong downsloping off the mountains have won the
day with record highs set across the Piedmont, though the mountains
are much closer to seasonal normals. The mountains have had their
own issues today with strong winds aloft resulting in gusts to 90mph
at Grandfather and over 50mph at Mt. Mitchell into the early
afternoon hours. Winds are beginning to subside with the gradient
slackening behind the front but may continue to gust like that
through early evening.

As the surface high pushes east tonight and over the Appalachians,
winds will swing around to the north and northeast, so we will lose
our downsloping component tonight and tomorrow. Upper ridging will
build back in over the area tonight and tomorrow as well. While
still nowhere near seasonal normals, overnight lows tonight behind
the front will be much more reasonable for January, with highs
Thursday progged to be 10-15 degrees colder tomorrow than those
today across the Piedmont (not much change, and actually maybe a
slight warming trend for the mountains).

A strong upper low over the southern High Plains will eject slightly
northeast through the near term, with surface low enhancement along
the Texas Gulf Coast. As the upper low lifts into the Plains, the
surface low will correspondingly lift into the Lower Mississippi
Valley. Warm front will lift into the Southeast and may bring some
initial precip into extreme western counties right at the end of the
period, but the real weather roller coaster starts in the short term.


As of 230 PM EST Wednesday...A long wave upper ridge axis will set
up along the East Coast, while a deep and broad mean upper trough
axis will persist across the Rockies and Plains. Two prominent short
waves will eject out of the trough and cross the CWFA within the
upper level southwesterly flow. The first will cross the area late
Thursday night, and the second during the day on Saturday. The first
wave will bring a warm/occluded front across the area, and will be
accompanied by an area of showers. The high-res models that go out
thru 12z Friday, show the shower activity being fast-moving, with
embedded stronger elements. There may be enough elevated CAPE for
isolated thunder, but no severe weather is expected. Temps will be
above normal Thursday night and Friday, with a lull in PoPs Friday

The second short wave will lift NE across the region on Saturday,
and looks to be accompanied by an activating warm front that will be
draped east to west across the Gulf states. As the wave ejects,
upstream energy will be carving out a vigorous upper low over the
Southern Plains. This will induce rapid cyclogenesis over/near the
TX panhandle. A very large warm sector will become unstable
Saturday, as the warm front lifts north. The NAM and GFS agree on
SBCAPE of 1000-2500 J/kg surging into LA/MS/AL thru the day. This
area will also have plenty of shear with 0-6 km bulk shear of 45-65
kts. It`s still a bit too far out to be certain what mode of
convection will likely fire, but whatever activity develops will
propagate NE toward our NE GA and western Upstate zones Saturday
evening. The Day 4 SPC outlook has a broad 15% area to our SW. This
certainly bears watching in the next couple of model runs and severe
storms mention may be needed in the HWO. PoPs were bumped up to
likely for most of the area on Saturday. Temps will remain well
above normal.


As of 200pm EST Wednesday:  Saturday night through Wednesday night
will be a period of unsettled weather.  GFS and EC agreement is
quite good through next Wednesday with a southern diffluent longwave
trough bringing moisture, showers, and thunderstorms on Sunday,
followed by a short-lived longwave ridge with clearing on Tuesday,
followed by the next progressive southern longwave trough due in by
early or late Thursday, though it could begin to affect the forecast
by Wednesday evening.  EC is about 12 hours ahead of the GFS with
the Thursday longwave, but the basic pattern of 2 longwave troughs
giving the region waves of weather is fairly consistent.
Precipitation Sunday/Monday looks generous with an inch or more
possible each day.  Precip on Sunday occurs with warm frontal
passage and possible thunderstorms, followed by wrap-around precip
and cool frontal passage on Monday.

Sunday afternoon has the best chance for thunderstorms, though the
best CAPE forecast is only around 700 j/kg, with a LI to -5.  Best
instability currently looks to be in the Piedmont areas at this
time, as low surface pressure associated with incoming longwave
brings abundant moisture in from the Gulf of Mexico.  While
instability is currently forecast to be modest, bulk shear is very
healthy at 50 to 65 kts Sunday afternoon, especially with the more
backed winds ahead of the surface low.

Minimum temperatures Sunday and Monday look to be in the 50s in
Piedmont areas, down to the 40s in the mountains, so there is little
risk of any winter precipitation.  With region far south of any cold
air masses, temperatures generally will be well above normal through
Wednesday, even behind the front that passes through with the
longwave trough on Monday.  Passage of that front will make Tuesday
the coolest day of the extended forecast, but still 10 degrees above

Surface winds will also be elevated with the passage of the storm
system Sunday and Monday, with 10 to 15 mph of southerly winds on
Sunday/Monday, becoming northwesterly behind the frontal passage on


At KCLT and Elsewhere: VFR through the period with mainly a wind
forecast. NW winds this afternoon behind the front will be
occasionally gusty at times, but should subside overnight as they
veer around to the N and NE. For KCLT, winds currently look to
remain on the N side of E through the end of the period just barely
but this will be refined in later issuances. Should see an increase
in high clouds early Thursday especially across the west as another
system approaches.

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

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
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      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




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