Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1002 am 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 tonight/...
as of 1000 am EST saturday: made a few minor adjustments to the
fcst with this update as latest guidance favors a slight increase
regarding arrival of precip onset tonight. Regional radar is
showing upstream echoes across northwest GA, however persistent
dryness in the bl is working to evaporate any falling hydrometeors
as said activity advects east. That said the bl will moisten with
time, thus blended in latest campop which introduced slight chances
across northeast Georgia by 6pm. From that point pops increase eastward
through the night with slightly faster timing. Otherwise, tweaked
T/TD and sky based upon latest obs/Sat trends which are impacted by
increasing mid/high cirrus by way of improving SW 500 mb flow.
Previous discussion: a deep cutoff 500 mb low will continue to dig
into northern Mexico today, with flat ridging atop the forecast
area. A series of vorticity maxima will track northeastward into the
Gulf Coast region, and supply plenty of upper level moisture today.
The increasing and thickening high clouds will temper Max temps back
a bit, with highs near normal in the Piedmont and slightly below
normal in the high terrain.
Tonight, the forecast soundings show moistening from the top down,
as flow turns out of the southwest. At the surface, cool high
pressure will linger over the area, while a low pressure system
brings wet weather to Texas and the lower MS valley. The models
agree on strong 700 mb warm air advection ramping up atop the forecast area
overnight, with enough moisture to support a band of light precip to
break out by daybreak Sunday. Temps will be tricky, as the northern
NC mountains and possibly some of the higher peaks in the central
mountains may support precip starting out as light snow. Given that
forcing should be modest and mainly in the mid-levels, while the
low-levels take some time moistening up, snow amounts are expected
to only 0.1-0.2" at most thru 12z Sunday. Pops will favor the
mountains and the western upstate, mainly in the likely range.
Chance pops east. Rainfall amounts will range from a trace east of
I-77 to around 0.3" in the southwest NC mountains.
Short term /Sunday 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 /15z Saturday through Wednesday/...
at kclt and elsewhere: a moist low pressure system will slowly eject
out northern Mexico and Texas today thru tonight, which will result in
a gradual increase in moisture atop the region from the top down.
Cirrus will gradually thicken and lower into mid cloud deck late
this afternoon thru this evening. Otherwise, winds will be fairly
light, as surface high pressure lingers over the area. Light winds
will favor a northwest to northeast direction, then turn to
southeast at the upstate taf sites and east-northeast at kclt. This evening,
ceilings will start to lower into the low VFR to MVFR range, with -ra
developing from west to east.
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.
15-21z 21-03z 03-09z 09-12z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% Med 68%
kavl high 100% high 100% high 100% high 92%
khky high 100% high 100% high 100% high 90%
kgmu high 100% high 100% high 100% Med 72%
kand high 100% high 100% high 100% high 97%
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: