Area Forecast Discussion
Issued by NWS Greer, SC

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214
FXUS62 KGSP 190549
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1249 AM EST Thu Jan 19 2017

.SYNOPSIS...
A warm front moving north over the region through Friday in
combination with low pressure headed north toward the Great Lakes
will bring more rain to our area, mainly tonight. 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.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1245 AM, high clouds will continue to increase overnight, but
should not have a huge impact on the nocturnal cooling cycle.
Nevertheless, due to the warm start, min temps are expected to
average 10-15 degrees above climo in most locations.

Otherwise, a surface high center will continue to push eastward over
the Appalachians overnight. Upper ridging downstream of the southern
plains system will persist over the area tonight through tomorrow as
well. Highs Thursday are progged to be 10-15 degrees colder than
those observed Wednesday across the Piedmont (with not much change,
and actually maybe a slight warming trend for the mountains).

The 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. A warm front will lift into the Southeast and
may bring some initial precip into extreme western counties right at
the end of the period.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
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
afternoon.

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.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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
normal.

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
Tuesday.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
At KCLT and Elsewhere: VFR conditions are expected through at least
00Z Friday. High and mid-level clouds will gradually increase during
the next 24 hours. Light NE winds at the start of the period will
gradually turn through E before becoming SE or S by early Thursday
evening. By late Thu evening, showers are expected to begin
spreading into the forecast area from the west, with categorical
-SHRA expected at all terminals other than KCLT before 06Z. Visby
and/or cigs restrictions cannot be ruled out before the end of the
period, but are more likely to develop between 06Z and 12Z Friday.

Outlook: Widespread rain showers will continue to overspread the
area Thursday night and early Friday. The very unsettled pattern
will continue through the weekend, bringing periods of rain and/or
restrictions. Heavy rain showers and perhaps thunderstorms are
possible Sunday.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
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       Low   56%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...SW
NEAR TERM...JDL/TDP
SHORT TERM...ARK
LONG TERM...WJM
AVIATION...JDL



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