Area Forecast Discussion
Issued by NWS Greer, SC

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212
FXUS62 KGSP 041505
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1005 AM EST Sun Dec 4 2016

.SYNOPSIS...
Increased moisture will cross our region from the west today and
linger into Tuesday. A strong cold front will arrive Wednesday night
bringing some of the coldest air of the season so far at the end of
the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM EST Sunday:  Light/moderate upglide induced,
frontogenesis enhanced precipitation continues across the
region this morning.  Profiles are modifying atop the northern
mtns where earlier light snowfall occurred, leading to a phase
change to sleep as the warm nose intrudes.  Expecting all precip
to change completely to liquid over the next 1-2 hours as the
inversion strengthens.  As for the fcst itself, opted to blend
in latest bcmav guid for temps thus yielding very flat diurnal
warming trends, generally less than 4-5 degrees at best regionwide.
Otherwise, no other sig changes were needed/made with this update.

As of 230 AM EST...A deep and vigorous upper low can be seen
still digging SEWD across northern Mexico this morning. This low
is tapping into tropical moisture from the Pacific and advecting
it into the southeast U.S. At the surface, a large area of high
pressure will shift east from the southern Great Lakes to roughly
along the Mid-Atlantic coast by early this evening. Moist isentropic
lift and WAA will strengthen a hybrid cold air damming wedge today,
keeping temps nearly steady in the upper 30s to mid 40s for most
of the area. A light to moderate steady rain is expect for most
of the day. Fortunately, limited instability and forcing should
keep rates under excessive levels today. QPF amounts thru 12Z
Monday look to range from about 0.7" north of I-40 to nearly 1.5"
in the SW mountains and adjacent GA/SC mountains with favored SLY
upslope flow. Forecast soundings still support high-elevation snow
this morning, especially in the northern NC mountains above about
5000 ft. However, temps should be above freezing everywhere but
the highest peaks. So little to no accumulation is expected. Warm
air advection should change all precip to rain by midday.

Tonight, a wave of weak low pressure will ripple east of the area,
veering the low-level flow to more westerly and allowing precip to
taper off overnight. There will still be a weak wedge holding on,
which will keep the area cloudy and perhaps somewhat foggy. Temps
will only drop a few degrees at most from the afternoon highs.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
As of 245 AM EST Sunday: We begin the short term with a shortwave
trough pushing through the Great Lakes with its attendant front
across the eastern Carolinas, surface high pressure over the Ohio
Valley, and a slowly filling upper low beginning to push northeast
from Mexico into TX, meanwhile pulling Pacific and Gulf moisture
into the coastal states as surface cyclogenesis is induced along the
TX Gulf Coast. Behind the initial front, we`ll be in a bit of a lull
though with the subtropical jet right over us, will keep the trend
of low chance pops south with at best slight chance across the
northern tier. We might see some breaks in the clouds as well with
highs only a couple of degrees below seasonal normals on Monday.

Meanwhile the surface high will cross the Appalachians during the
day and begin to ridge down the Eastern Seaboard in a diabatically
enhanced classical CAD setup. The Gulf Coast low will lift northeast
in a Miller B scenario late Monday into early Tuesday, with
widespread moisture overtopping the cold dome. PW values between 1-
1.5" can be expected by Tuesday morning across the area, the upper
end of which is pretty darn close to record PW values. This is
fairly short-lived with the fast-moving system but could bring some
hefty rainfall amounts to portions of the Piedmont as the southern
of the two Miller B lows pushes northeast in the predawn hours. 6-hr
QPF values are 0.75-0.9" across the GA/Carolinas Piedmonts in our
area from 06z-12z Tuesday so this would be the period of greatest
concern for impacts from heavy rainfall. Storm total QPF ranges from
about 1.5" across the northern tier to almost 3" across the southern
tier. Additionally, with the damming in place and strong
ageostrophic adjustment, winds will pick up out of the NE Monday
night, with sustained winds 10-15kt and gusts up to 20kt. Certainly
nothing close to advisory criteria or anything like that but worth
noting.

Precipitation will exit quickly to the east during the day on
Tuesday, but with lingering moisture across the mountains with NW
surface flow and and SW flow aloft. Highs Tuesday will be highly
dependent on if the damming is able to erode earlier than
anticipated, but since usually guidance is too fast at eroding the
wedge, continued to lean slightly on the cool side.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 145 AM EST Sunday:  The strong cold front will arrive from the
west by late Wednesday. Ahead of the front Max temps will be about a
category above normal which will make Wednesday the mildest day of
the whole week. There will be no inflow from the Gulf as low level
wind will be from a general west direction Wednesday into Thursday
morning shifting to NW by PM Thursday into Friday.  The moisture
starved environment associated with the cold front will yield very
little precip. Based on the latest run of the GFS, only precip will
be in the mountains being light snow behind the front with falling
thickness values. All that shrivels away by early Friday. A little
more precip on the ECMWF but that also ends abruptly early Friday
with much drier and colder air moving into the area.  Expect cold
air advection Friday and then light to no wind on Saturday as the
center of the cold surface high will be over the Carolinas and VA
early Saturday. Both the GFS and ECMWF have a wintry precip producer
arriving to our region later on Sunday lingering into next Monday.
That is after the current forecast so stay tuned for how this
evolves in the days ahead.

Temps a little above normal Wednesday then falling to 15 degrees or
more below normal for Friday and Saturday. Some moderation in Min
Temps Saturday night as cloudiness increases ahead of the next
system.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
At KCLT and Elsewhere: As often happens with the onset of widespread
light rain, conditions don`t just go down gradually. And sure
enough, the Upstate sites and KAVL have developed a LIFR stratus
under the rain, much earlier than the guidance was indicating. I
expect conditions to eventually prevail IFR/LIFR by midday at all
sites, as steadier moderate rain overspreads the region. A weak CAD
wedge will keep sites socked in with low CIGS and reduced VSBY thru
tonight, even though rain should taper off from west to east after
sunset. Winds will be light out of the NE to ENE across the piedmont
sites, and out of the SE at KAVL.

Outlook: A brief lull is possible Monday, then another round of
heavier rain and widespread restrictions on Tuesday. Brief dry
weather is expected on Wednesday, with another front approaching
from the west.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       Med   60%     Med   65%     Med   75%     Med   74%
KGSP       Med   77%     Med   75%     Med   71%     Med   74%
KAVL       High  81%     Med   71%     Med   75%     Med   64%
KHKY       Med   73%     Med   71%     Med   75%     Med   63%
KGMU       High  84%     Med   73%     Med   70%     Med   74%
KAND       Med   69%     Med   76%     Med   70%     Med   74%

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...DEO
NEAR TERM...ARK/CDG
SHORT TERM...TDP
LONG TERM...DEO
AVIATION...ARK



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