Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
316 am EST Thursday Dec 12 2013
relatively cold and dry high pressure will continue over the region
today through Friday and then move off the Carolina coast. Another
low pressure system should arrive from the west on Saturday bringing
widespread precipitation to the region over the weekend. Expect
another high pressure system to bring dry weather through the middle
of next week.
Near term /through tonight/...
as of 215 am EST...water vapor imagery shows a shortwave just west
of the Appalachians early this morning. This feature...accompanied
by very limited moisture...will move east of the mountains by 12z. The
main impact will be a briefly tightening pressure gradient behind
the wave that will generate gusty northwest winds across the northern NC mountains
the winds should remain below advisory levels. In addition...a
reinforcing surface cold will continue to sweep southeast of the area by
daybreak. This will leave cool thicknesses in place across the area
to support maximum temperatures 5 to 10 degrees below climatology over the
foothills and Piedmont today...and 10 to 15 degrees below climatology
across the mountains little more than high cirrus is expected
early...and this should move off to the southeast through the day along
with the departing upper jet axis.
Surface high pressure will become centered directly over the southern
Appalachians tonight to produce clear skies and light winds. The
good radiating conditions will yield min temperatures in the upper teens to
around 20 in the mountains...with solid 20s across the foothills and
Short term /Friday through Sunday night/...
as of 315 am Thursday...the short term period will initialize Friday
morning with high pressure in place across the east and an upper
trough digging across the Desert Southwest. The above mentioned East
Coast ridge will shift out to sea on Friday as the upper wave
migrates east. Guidance continues to agree with regards to the
timing of precipitation onset associated with this next system.
Expecting light showers early on Saturday morning across the
southwest NC and northeast Georgia mountains as isentropic ascent ahead
of the parent low increases. Therefore...will carry chance probability of precipitation
early on Saturday morning across the western zones. Low
temperatures on Saturday morning should be in the middle to upper 30s
across the majority of the forecast area. However...guidance
continues to indicate favorable freezing rain temperature profiles across
portions of the northern NC mountains for a few hours early Saturday
morning with all precipitation changing to rain around daybreak as
warm advection prevails. Probability of precipitation will ramp up to solid categorical
levels by midday across the entire region as light to moderate
showers overspread the region.
Additionally...forecast soundings indicate marginal middle level
instability through the profile across the Southwest Mountains
early on Saturday as the surface low approaches and shear
maximizes. Therefore...will mention chances for isolated thunder in
the forecast across these zones...spreading east through the day as
the surface low and upper support pass through. As the system
deepens and ejects up the East Coast Sunday morning...probability of precipitation will
decrease from west to east. Will keep mention of slight/chance
level probability of precipitation across the high terrain on Sunday as moisture wraps
around the departing low yielding potential for a brief nwfs event.
Not expecting any significant accumulations out of either the
earlier onset freezing rain...nor the later period nwfs event...thus
generally less than a tenth of an inch of ice accumulation and less
than an inch of snowfall.
Long term /Monday through Wednesday/...
as of 220 am EST Thursday...the global models are in good agreement
with the overall synoptic pattern throughout the medium range
period. 500 mb heights will rise across the region on Monday as an upper
trough pushes off the Atlantic coast. Upper pattern then becomes
quasi-zonal by Monday night and continue that way through Tuesday. An
upper trough over the upper Midwest Tuesday night is expected to dig
into the southern Appalachians by Wednesday...and move off the
Atlantic coast by Wednesday night.
At the surface...broad high pressure will be centered across the southeast
bringing dry weather and moderating temperatures to the region Monday into
Tuesday. A dry cold front will then approach from the northwest and crosses
the region on late Wednesday. The GFS brings light northwest precipitation to the
northern NC mountains with this feature while the European model (ecmwf) keeps most of the
area dry. Given the uncertainty...have mentioned slight chance probability of precipitation
of rain and snow mix over the NC mountains Wednesday night and kept elsewhere
dry. Another high pressure will build in behind the front beyond day
7. Temperatures will start out 3-5 degrees below normal on Monday
and a gradual moderating trend expected through Wednesday.
Aviation /08z Thursday through Monday/...
at kclt...a weak cold front now southeast of kclt will allow winds to
remain solidly northwest to north going forward. Speeds will pick up with
mixing later this morning...but generally remain 10 knots or less
through the day...with the gradient relaxing late. Little more than
few to scattered cirrus is expected early in the period.
Elsewhere...solid northwest flow is expected as the passing cold front has
moved through the region early this morning. The gradient will
tighten across the mountains through daybreak...and occasional wind gusts
to 18 knots will occur at kavl through at least middle afternoon.
Elsewhere...expect northwest to north winds at less than 10 knots...becoming light
toward evening. Any early period cirrus will clear to the southeast through
Outlook...dry high pressure will remain over the region through
Friday. A storm system will move from the Southern Plains to the southern
Appalachians on Sat...when restrictions in rainfall will become most
likely. Conditions will dry out from the SW on Sunday...with dry
high pressure returning for Monday.
08-14z 14-20z 20-02z 02-08z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% high 100% high 100%
khky high 100% high 100% high 100% high 100%
kgmu high 100% high 100% high 100% high 100%
kand high 100% high 100% 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: (must be lower case)