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fxus62 kgsp 121157 

Area forecast discussion
National Weather Service Greenville-Spartanburg SC
657 am EST Tue Nov 12 2019

an Arctic cold front will move east of the area by this afternoon.
Dry and very cold high pressure will then settle over the region
Tuesday night through Wednesday, and warm only slightly Thursday. An
upper-level low pressure system will develop over the deep south
late in the week, with an associated surface low pressure center
developing over the coastal waters off the southeast coastline.
Moisture and light rain from this system could brush the Piedmont
from Thursday night into the weekend.


Near term /through tonight/...
as of 655 am: the long anticipated Arctic cold front was near the
foothills as of this writing. Overrunning moisture with limited Gulf
of Mexico access continued to produce rain/snow behind the front
which is often classified as an anafront. Temperatures have
continued to plummet behind the front temps dropping around 10
degrees in the past 3 hours near the Tennessee border. Rain has turned to
snow across higher elevations mountains with snow levels expected to
continue to fall this morning. Current Winter Weather Advisory looks
good especially for the higher terrain.

Weak upglide well ahead of the front will continue to support
isolated to scattered showers ahead of the main band. The main band
of precipitation will move into the mountains through mid morning,
spreading east into the Piedmont from mid morning through early
afternoon. As this front seems to be a bit colder than advertised,
have blended in rap/namnest with nbm to cool things off a bit
quicker behind the front. In fact, many areas east of the mountains
will start the morning in the low 50s, only to drop to near 40 this
afternoon. This will support a bit quicker turnover from rain to
snow across the mountains. Also can't rule out a brief turn over to
a mixture of precip or snow into the NC foothills into the northwest
NC Piedmont if moisture can hang on long enough. There continues to
be the potential of a brief freezing rain/sleet mixture across the
mountains before turning over to snow. Backward trajectories
originating over the length of Lake Michigan and even north into
Lake Superior suggest at least flurries if not snow showers will
linger well into the afternoon if not early evening near the Tennessee
border. Any additional accumulations during this time period, if
any, will be light. Given recent warm weather, snow may having
trouble sticking outside elevated and grassy surfaces across Lower
Mountain valleys especially away from the Tennessee border. However,
with temperatures dropping off quickly this evening, a flash freeze
is still a real concern for any areas that don't dry out across the
mountains, especially above 3000 feet. Another area to watch will be
the northwest NC Piedmont, possibly extending into the I-77 corridor since
precipitation is expected to continue into the afternoon in these
areas with temperatures falling near to below freezing in the early
evening. All told, not much change in the thinking for snow totals.
However, relatively low confidence exists given the quick hit nature
of the front. Liquid to snow ratio will likely be 8:1 at lower
elevations, possibly upwards of 12-14:1 at higher elevations. All
told 2-4 inches is the best bet above 4000 feet locally down to 3000
feet near the Tennessee border. Generally a dusting to an inch is expected
across Lower Mountain valleys including Asheville. The Winter
Weather Advisory for most of the mountains will be maintained

Gusty northwest winds up to 40 mph across the mountains and up to 30
mph elsewhere through this evening will make it feel much colder
than the actual temperatures, especially tonight with temperatures
dropping into the teens across the mountains and well into the 20s
elsewhere. In fact, it will feel like the single digits across
mountain valleys and teens east of the mountains by late this
evening. Lows tonight will challenge daily mins, especially at gsp
and clt.


Short term /Wednesday through Thursday night/...
as of 315 am tuesday: although upper heights will be on the rise
early in the short term, this trend will not last long, as the next
round of short waves will reinforce the eastern long wave trough by
the end of the period. In the interim, Arctic high pressure
transiting the southeast and mid-Atlantic will support continued
well-below normal temperatures, with maxes and mins expected to be
in the neighborhood of 20 degrees below climo through the period.

With the approach of aforementioned short wave energy, cyclogenesis
is expected near the southeast coast late in the period. Models in
general continue to struggle with the details regarding this
feature, including in how far north and west to spread associated
precip shield. However, there's enough of a signal there to continue
a mention of 20-40 pops across roughly the southeast third of the
forecast area Thu night. If this were January, with this type of
anomalous air mass to go along with forcing and moisture, we'd be in
business regarding winter wx possibilities. But, in this scenario
any precip across the Piedmont would almost assuredly fall as a
chilly rain.


Long term /Friday through Monday/...
as of 330 am tuesday: small pops for precip potential associated
with coastal cyclone will continue across roughly the southeast
third of the forecast area through early Saturday, at which point
the cyclone should be pulling away from the Carolina coast.
Otherwise, rising upper heights/building ridge developing across the
eastern Seaboard...downstream of the next round of central conus
height falls, will result in moderating temps late in the week into
early next week. Having said that, temps will remain below normal,
generally by 5-10 degrees, especially across the Piedmont during the
first half of the period, where cloud cover associated with the
coastal storm will limit the diurnal heating cycle. After weekend
drying, yet another coastal cyclone may develop near the end of the
forecast period in response to the next round of height falls.
However, models are generally painting a dry picture for our
forecast area on day 7/Monday. This is a bit of a different picture
than was being painted by yesterday's 12z guidance, but plenty of
run-to-run model inconsistency can be anticipated for that time
frame, as has been the case for this late week's storm system. That
being the case, a slight chance pops has been retained for much of
the forecast area for Monday, even though it's not really supported
by current deterministic global model guidance.


Aviation /12z Tuesday through Saturday/...
at kclt and elsewhere: moderate confidence in current taf package
with lowest confidence in cigs through 18z. A strong Arctic front
will bring widespread rain to the area peaking near and just behind
the frontal passage through 18z. Low MVFR to IFR cigs/vsbys are
likely at most sites for a couple of hours or so near the front.
Gusty northwest/north winds are expected at all sites behind the front until
near the end of the taf period when gusts may begin to drop off. At
kavl, a -snra or -shsn is likely at sometime through 16z with any
light accumulations unlikely to affect runway conditions given
recent warm temperatures. A very brief mix over is also possible at
khky and kclt. High pressure building into the area tonight will
support lighter north/NE winds with VFR conds prevailing. Early morning
fog or stratus will be possible Wednesday, focused across sheltered
mountain valleys.

Outlook: VFR continues through at least Thursday with Mountain
Valley fog and stratus will be possible each morning. Another system
may bring rain and associated restrictions beginning Friday.

Confidence table...

12-18z 18-24z 00-06z 06-12z
kclt high 92% high 90% high 100% high 100%
kgsp high 85% high 100% high 100% high 100%
kavl Med 79% high 98% high 98% high 100%
khky Med 65% high 100% high 100% high 100%
kgmu high 80% high 100% high 100% high 100%
kand Med 78% high 97% 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:



records for 11-13

Maximum temperature min temperature
station high low high low
------- ---------- ---------- ---------- ----------
kavl 75 1964 32 1906 58 1929 13 1911
kclt 81 1931 40 1920 63 1879 21 2013
kgsp 81 1909 40 1920 61 1929 20 1906

Records for 11-14

Maximum temperature min temperature
station high low high low
------- ---------- ---------- ---------- ----------
kavl 76 1999 32 1906 60 1929 16 1986
kclt 80 1879 37 1976 63 1961 21 2013
kgsp 79 2007 36 1976 62 1929 20 1906


Gsp watches/warnings/advisories...
NC...Winter Weather Advisory until 7 am EST Wednesday for ncz033-



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