Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
139 PM EST Sat Dec 3 2016
increased moisture will return from the west on Sunday and linger
into Tuesday. A strong cold front will arrive early Thursday
bringing some of the coldest air of the season so far at the
end of the week.
Near term /through Sunday/...
as of 130 PM EST saturday: a closed 500 mb cyclone centered over northwest
Mexico continues to deepen as moisture lifts N/NE across the MS
Delta Region into the the Tennessee/Ohio valleys. Surface high pressure
remains centered over the southern/central Appalachians this
afternoon and thus reinforcing a dry llv airmass. However, given
the aforementioned moisture advection and swly flow aloft, the atm
will moisten with time from the top down. As such, latest vissat
imagery indicates modest amounts of mid/high altocu/cirrus streaming
into northeast Georgia and the southern Appalachians at present time.
This pattern will continue into the evening/overnight with pops
increasing later this afternoon from the west with likely levels
favored west of i77 by 12z, then spreading across the entire fcst
area by midday Sunday.
Profiles across the region during this time frame so support all
ra with the exception of higher terrain locales above 4-5kft.
For those areas, expecting ptype phase changes from ra by early
morning to ra/sn or all sn by mid/late morning, especially across
the northern mtns. Some light accumulations are possible in this
region, however generally less than 1 inch. Temperatures will
slowly warm into late morning across the entire fcst area leading
to all ra by midday as highs top out in the upper 30s across the
mtns to upper 40s over the Piedmont. Rainfall amounts through
Sunday afternoon are fcst to be around 1-1.25 inches across
the southwest/central NC mtns and northeast GA, tapering down
to the east with a half to quarter inch favored at gsp and clt
Short term /Sunday night through Tuesday/...
as of 245 am EST saturday: the short term begins with weak ridging
aloft atop a surface high stretching from the Carolinas to Canada,
with a sharp trough pushing through the center of the country. Split
flow from the cutoff upper low over northwest Mexico will also continue to
Pump Gulf/eastern Pacific moisture into the southern states. Pops
will be on the increase as we begin the short term, with the initial
main concern being wintry precip in the northern mountains (and a
little in the balsams). BUFKIT soundings continue to indicate a deep
near freezing isothermal layer for ktnb (boone) leading to some
brief wet snow, but as temperatures rise this should switch over
quickly to all rain by mid-morning. 90th percentile probs are barely
over 1/2" for snow during the 06z-18z Sunday time frame and our
storm total snow grids are less than 1/4". Can't rule out some
isolated areas with more than that but it certainly wouldn't last
long as temperatures rise above freezing. However, with the surface
high in place and a transient damming-like feature, temps won't rise
all that much and should remain well below seasonal normals as pops
continue to rise.
As the northern shortwave slowly damps and pushes east, it will push
the bulk of the precipitation south, with higher pops remaining in
our southern zones but should see a good lull in precip along the
northern tier Monday midday with only slight chance pops, but
likelies remaining south. The Mexico cutoff will be working its way
northeast into Texas on Monday with a resurgence in moisture lifting
out of the Gulf as cyclogenesis is induced along the Texas Gulf Coast.
This will lift rapidly northeast in a Miller b-type pattern as high
pressure over the Ohio Valley crosses the Appalachians and ridges
quickly down the eastern Seaboard Tuesday in a diabatically-enhanced
classical cad scenario under strong confluent flow aloft. Between
the cad and the moisture, temperatures will continue below seasonal
normals through Tuesday.
For now, it looks like The Wedge front should set up to our south,
leaving US solidly in the cold dome, and it does not look like
thunder will be of any concern on Tuesday, but if The Wedge front
begins eroding more quickly it may be something we'll have to look
into. However there is enough agreement in guidance that this seems
By the end of the short term, precipitation will be rapidly exiting
to the east and northeast with dry air filtering in behind it,
leaving only some lingering moisture in the mountains with northwest
surface flow and west-northwest flow aloft. Through the entire event, mainly
going with wpc qpfs, looks like storm totals range from just over 1"
along the northern tier to pushing 3.5" south. A good 1.5-2.5" for
the southern mountains and wildfire-stricken areas, which hopefully
will continue to help with suppression efforts.
Long term /Tuesday night through Friday/...
as of 140 am EST saturday: period begins 00z Wednesday with the
apparent Miller b low pressure systems moving NE of our region
ending all rain across our area Tuesday night. Some upslope precip
will linger along the Tennessee border for a few hours Tuesday night, but
all of this light rain should end before sunrise Wednesday. The
secondary cold front which will be the leading edge of a much colder
airmass will be approaching from the west Wednesday night. This
front is forecast to be moving east of I-77 by Thursday afternoon
and temps will be dropping in the NC mountains during the day
Thursday. Expect lows Thursday night in the NC mtns in the teens to
around 20 then only reaching the 30s for highs on Friday. The GFS is
a bit faster in bringing the cold air in while the European model (ecmwf) is a little
slower but both models have light snow in the NC mtns Thursday
night. The GFS ends this light snow by late Friday morning while the
ec keeps it going at least in the northern mtns until Friday
evening. Apparently the GFS has been performing best in recent days
so will lean toward ending the precip early rather than later. Very
dry air in place for most of next weekend as the center of surface
high pressure transits over our region.
Max and min temps a little above normal Wednesday then plunging to
10 degrees below normal Friday. Friday night mins could be at least
15 degrees below normal.
Aviation /19z Saturday through Thursday/...
at kclt and elsewhere: a mixture of VFR/MVFR and possibly IFR is
expected through this taf cycle as moisture advects into the region
from the southwest. A deepening system moving through northern
Mexico will continue to loft moisture NE over the southern states
through the period. As such, am expecting said moisture to lift
isentropically atop a broad region of high pressure. This will
result in increased chances for ra into/thru the overnight with
cigs/visb falling into restrictive flight categories. These
restriction levels and timing in the tafs are based upon latest
cam guidance and fcst soundings. Once conditions deteriorate,
restrictions are favored at all sites through the period.
Winds will remain light vrb this afternoon, possibly veering sely
at the Piedmont sites to include kclt, then should back nly for
the remainder of the taf cycle.
Outlook: moisture will gradually spread into the region through
Sunday leading to increasing chances for precipitation and
restrictions. A brief lull is possible Monday with the best chance
for heavier rain and widespread restrictions on Tuesday. Brief dry
weather on Wednesday, with another front approaching from the west.
18-24z 00-06z 06-12z 12-18z
kclt high 100% high 100% high 91% high 86%
kgsp high 100% high 100% high 92% high 98%
kavl high 100% high 100% high 95% high 91%
khky high 100% high 100% high 88% high 87%
kgmu high 100% high 100% high 91% high 98%
kand high 100% high 97% high 86% high 98%
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: