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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
1008 am EST Tue Dec 6 2016

low pressure will track northeast of our region today with high
pressure building across the area tonight and Wednesday. Expect a
strong cold front to approach from Tennessee Wednesday night and
cross the Carolinas on Thursday. This front will bring the coldest
air of the season so far for Thursday night through Saturday.
Temperatures returning to near normal early next week ahead of the
next cold front.


Near term /through tonight/...
as of 10 am EST tuesday: satellite imagery shows the dry slot on
water vapor imagery about to enter northeast Georgia and the wrn upstate
of SC. The loss of the deeper moisture will bring an end to some of
the better precip across the region from SW to NE through the middle
part of the day. Low level isentropic lift and upslope flow over the
top of the cold air damming wedge will maintain light rain/drizzle
over much of the region into the afternoon, especially the foothills
and mtns. The fcst reflects a lowering of the precip chance in spite
of the continuing drizzle, which should be interpreted as a decrease
in the chance of measurable rain. Temps will remain nearly steady.

Otherwise, guidance wants to erode the cold dome too quickly and
thus warms temperatures up a little more this afternoon. Once the
upper low, which by that time will be more of an open wave, passes
to our northwest this afternoon, we'll lose the isentropic/
orographic upglide with precipitation reinforcing the cold dome and
erosion will begin, so there definitely remains some bust potential
with temperatures, but if we go down, we go down together since
afternoon his are pretty well collaborated with surrounding offices.

As to the question of thunder, just really not feeling it this
morning. The surface inversion is very strong and while it can be
argued that lapse rates above 850/875ish mb might support some
elevated cape and indeed Storm Prediction Center has about 2/3 of the forecast area in
general thunder, but we start losing upper level moisture just after
daybreak this morning in southwest zones where elevated instability
seems most likely. Just doesn't seem to add up so have not included
any thunder in the zones. Never say never especially when dealing
with weather of course.


Short term /Wednesday through Thursday night/...
as of 200 am EST Tuesday...a broad longwave trough will persist
across the eastern 2/3rds of the Continental U.S. During the short term, with
strong shortwave energy diving in from the west and shifting the
trough axis eastward. This trough will be accompanied by a strong
cold front, which will cross the County warning forecast area on Thursday. Low-level flow
will turn out of the SW with some warm air advection and moisture to support
variable amounts of cloudiness on Wednesday into Wednesday night.
The front will have little moisture to work with, however. The 00z
European model (ecmwf) is dry with the fropa, while the GFS and NAM have a little
qpf, mainly in the western zones. The GFS is about 6 hours quicker
than the NAM. So all this disagreement makes the pop forecast
challenging, but still expect the band of precip (if there is any)
to push into the mountains around daybreak Thursday. Even if the
wetter NAM verifies, it looks like a very quick-moving line of
showers with only a few hundredths to about tenth of an inch.
Whatever precip does fall, temps will support rain in the valleys
and rain/snow mix in the high elevations, but with little to no snow

Temps will be near normal on Wednesday and above normal Wednesday
night with increasing clouds. Then noticeably colder in the
mountains Thursday with gusty northwest winds. Winds will linger thru
Thursday night as temps continue to fall within strong cold air advection. So
elevations above about 3500 ft may see wind chills dip below zero,
especially near the Tennessee border. Min temps Friday morning will be the
coldest so far of the season, ranging from the single digits and
teens in the mountains to the 20s across the entire Piedmont.


Long term /Friday through Monday/...
as of 130 am EST tuesday: good cold air advection continuing at the
start of this period Friday morning with northwest wind at 850mb varying
from 15 to 35kts. The center of the surface high Friday morning over
the Mississippi Valley then centered over our area Saturday morning
with little or no wind. Temperatures will be 10 to 20 degrees below
normal through Saturday. Wind chills in the single digits for higher
elevations Friday night before the wind dies down.

As the high moves offshore on the mid Atlantic Saturday into Sunday,
return flow from the Gulf feeding into the Mississippi Valley will
begin ahead of the next cold front. Scattered upslope showers may
begin late Sunday and Sunday night from near Clayton Georgia to Tryon NC.
The bulk of the precip with this system should be on Monday
depending on which model is presenting the evolution. The GFS is the
faster model bringing frontal moisture across the NC mtns Sunday
night then slowly drying out this moisture as it reaches the
Piedmont by Monday afternoon. The European model (ecmwf) brings in deeper moisture
late Monday across our whole area then shifts it east late Monday
night. The GFS has our region dry Monday night. Of course, this is a
week away and many changes will occur as model data evolves in the
next several days.

Temperatures of course 10 to 20 degrees below normal Friday and
Saturday then moderating to around normal Monday.


Aviation /15z Tuesday through Saturday/...
at kclt and elsewhere: widespread IFR to LIFR conditions across the
area this morning with -ra as cold air damming remains firmly
entrenched. NE winds 7-12kt with gusts 15-20kt prevail as well for
all but kavl (where southeast winds prevail). Cigs will remain low with
widespread restrictions through a good chunk of the day, with slow
but brief improvement this afternoon and evening as the damming
erodes. Cigs will improve but late in the period all guidance drops
vsby again. Should see additional improvement beyond the end of the
period. Winds should shift north/northwest as the damming erodes, with speeds
dropping to around 5kt.

Outlook: expect improving conditions on Wednesday behind the front
with dry air filtering in to scour out the low level moisture.
Another front will approach on Thursday with some restrictions
possible. Dry and much colder through the weekend.

Confidence table...

15-21z 21-03z 03-09z 09-12z
kclt high 86% high 98% Med 77% high 100%
kgsp Med 60% high 95% high 85% high 94%
kavl Med 65% high 93% high 81% high 82%
khky Med 76% high 93% Med 79% high 89%
kgmu Med 70% high 91% high 80% high 88%
kand Med 61% high 98% high 88% high 92%

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:



Gsp watches/warnings/advisories...


near term...PM/tdp
short term...Arkansas
long term...deo

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