Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 271954

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
254 PM EST Sun Nov 27 2016

High pressure will weaken and move offshore into Monday before deep
layered moisture increases ahead of an approaching cold front. A
much needed rainy pattern will persist across the region through
Wednesday night...with cool and dry high pressure returning Thursday
and lingering through the weekend.


The upper pattern over the eastern Conus will remain somewhat
progressive over the next 24 hours or so, before coming to a
grinding halt by the end of the period. Cirrus will continue
streaming into the forecast area from the west through tonight
while gradually thickening. Meanwhile, increasing southerly flow and
low clouds will begin advecting low level moisture into the area by
daybreak. This should not have a big impact on tonight`s min temps,
but the cirrus should (although to what degree is always a bit of a

Southerly flow and moisture will gradually increase through the day
Monday, resulting in increasingly moist mechanical lift near the
southern escarpment of the Blue Ridge. Pops will gradually ramp up
through the day, reaching solid chance to low-end likely by the end
of the day. The leading edge of a low level wind maximum (H8 winds
of 50 to 60 kts) will begin translating across the southern
Appalachians by the end of the period. The warm advection/shallow
mixed nature of these events typically results in strong winds being
relegated to the exposed peaks and ridge-tops, mainly above 4 kft,
with lower elevation downslope/mtn wave effects typically being
confined to areas north and west of our forecast area. There`s
nothing that leads me to believe that this one will be any
different, although the strength of the low level winds certainly
gives one pause. All that being said, the winds in the
aforementioned exposed areas will certainly howl, likely gusting to
60 mph at times across the high elevations near the TN border. A
high elevation wind advisory may become necessary at some point, but
we do not plan to issue one at this time.

Otherwise, max temps will be a bit tricky on Monday, as the day will
begin with extensive low clouds, but these may tend to dissipate
late in the day across our southern and eastern areas, while high
clouds should remain thick across the entire area. Our best guess is
that maxes will be a solid 5 degrees below climo across the heart of
the CWA, and a little closer to climo across the southern and
eastern zones.


As of 250 PM Sun: Latest satellite water vapor loop shows an
amplifying system across the Pacific coast. In addition, a large
stream of moisture is stream NE out of the tropical Pacific across
northern Mexico across the southern Great Plains. This system will
bring the first round of heavy rain to the southern Appalachians
Monday night through Tuesday. Beginning Monday night, short range
guidance indicates that SE H85 winds will increase to around 50 kts.
The combination of increasing deep moisture and strengthening WAA
winds should support widespread heavy upslope showers late Monday
into early Tuesday. Precipitable water is forecast to increase to 1 to
1.1 inches by late evening, supporting rainfall rates as high as
1.5/6 hrs across the upslope areas early Tuesday morning. The center
of 530 DM H5 low should pivot from the Northern Plains into the Mid
West on Tuesday. The core of a 140 kt should slide across the Ohio
River Valley, resulting in a band of jet divergence to pass over the
southern Appalachians during Tuesday morning. A pre frontal band of
moderate to heavy showers should push over the mtns after sunrise,
with the eastern motion gradually slowing through the rest of the
day. The short range guidance generally agrees that the band will
exist in a region of llvl winds nearly parallel with mid level
heights. The band should gradually dissipate during Tuesday
afternoon and evening. Rainfall with this first round is expected to
spread 1.5 to 2.5 inches across the NC mtns with a half inch or less
east of I-77. Temperatures across the CWA will feel like a WAA, with
highs generally in the mid to upper 60s.

Tuesday night, the axis of a longwave trough will dig across the
Great Plains, supporting the development of a frontal wave across
the southern Mississippi River Valley. H85 winds ahead of the wave
is forecast to back from the SE and strengthen to 40 kts. This will
begin the second round of moderate to heavy upslope rain showers
across the mtns. However, this second round appears more impressive
as the pattern will like draw deep moisture from across the Gulf of
Mexico. On Wednesday, the sfc low should rapidly track NE across
eastern TN / KY. As the low pulls north, an associated cold front
should sweep across the southern Appalachians. Forecast soundings
and model fields indicate that a narrow band of CAPE will precede
the cold front, supporting a mention of TSRA. In addition, the mid
level trough will approach from the west, spreading a wild field of
synoptic scale forcing across the CWA. Moderate to heavy showers,
TSRA, should slowly push across the region, resulting in good
rainfall rates through most of Wednesday. Storm total rainfall across
the mtns should generally verify with 3-5 inches, upslope areas near
SE facing slopes could see values range from 6-9 inches. Rule of
thumb for isolated to scattered debris flows and mud slides is 5
inches in 24 hours. It is possible that some of our burn scar areas
could see rates that may trigger slides. Rainfall will come to an
end around sunrise Thursday.


As of 215 PM EST Sunday: the extended begins Thursday morning in the
wake of the second system which will be rapidly exiting the area.
The new 12z ECMWF is a little slower than the GFS but still all pops
are out of the area by Thursday afternoon. Strong WSW flow continues
aloft with a modified surface high pressure building in from the Mid-
South so even with the CAA temperatures on Thursday will be a couple
of degrees above seasonal normals. Another shortwave, this one dry,
rotates around the base of the upper low over eastern Canada
Thursday night into Friday morning so we`ll see a more significant
difference in temperatures then.

Meanwhile a split flow pattern develops with a strong closed upper
low over the Desert Southwest. Another round of significant moisture
streams up from the Gulf and eastern Pacific, spreading across the
Southern Plains into the Lower Mississippi Valley over the weekend.
Some big differences (not that we`re surprised) with how the
operational models handle this situation, with the ECMWF streaming
moisture all the way up to the Ohio Valley by Sunday as it has the
upper low phasing with a shortwave coming out of Canada. The GFS
pushes the Canadian shortwave east with no phasing of the two
systems; instead the Canadian shortwave pushes the Gulf moisture
farther south and holds off on introducing precip into the Southern
Appalachians until the upper low lifts into the region, beyond the
end of the period. Both have another round of high QPF values (like
another 3-4") , it`s just that the ECMWF is much faster. The
ensembles aren`t really much help as, for example, the GFS ensemble
is much more similar to the operational GFS and vice versa. Will
have to watch this closely but there remains heightened concern
about the amount of rain we might continue to receive (we needed
rain for sure, but it would be nice if it were spread out a little
more...but I guess we can`t be too picky). Other concern will be
with some p-type issues in the northern mountains with the cold air
behind the dry shortwave later this week and then the incoming
moisture early next week. Introduced a little snow and rain/snow mix
wording but obviously this is way too far out to really hang our
hats on much.


At KCLT and elsewhere: VFR conditions are expected through the
period, except perhaps at KAVL where smoke from a wildfire over SC
may occasionally reduce visby to MVFR. While high clouds will
continue gradually overspreading the region from the west, moisture
surging into the area on increasing southerly flow aloft is expected
to result in a cloud deck in the 030-040 range spreading over the
area from around daybreak through mid-morning on Monday. It`s
possible that cigs could lower to MVFR in some areas by the end of
the period, but timing of this is uncertain attm. Otherwise, light S
to SE winds are expected in most areas through the period.

Outlook: Chances for precip and restrictions will increase
throughout Thu afternoon, with widespread rainfall and associated
restrictions expected at least periodically from Monday night
through Wednesday. Drying is expected during late week.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High  88%
KAVL       High  83%     High 100%     High 100%     High  91%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High  88%
KAND       High 100%     High 100%     High 100%     Med   78%

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:


A strong frontal system is expected to push in from the west late
Monday, more or less affecting the region through early Thursday.
Southerly winds will ramp up Mon ahead of the front and remain
strong into Tue. This pattern should bring deep moisture from the
Gulf of Mexico. The combination of deep moisture, upslope flow, and
a large area of synoptic scale forcing indicates precipitation may
start as early as midday Monday over the mountains, with widespread
rain across the area on Tuesday.  Tuesday evening may see a lull in
rain, with another round expected to develop overnight and last thru
Wednesday. Guidance indicates that the potential exists for 2-5
inches of total rain across the mtns and foothills for the Monday
through Thursday period, with the higher amounts of rain expected
along south or southeast facing slopes. The Piedmont is expected to
see 1 to 2 inches of rain.


NC...Fire Danger Statement until 7 PM EST this evening for NCZ033-


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