Scientific Forecaster Discussion
fxus62 kgsp 132335
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
635 PM EST Wed Dec 13 2017
a dry cold front will cross the area from northwest to southeast
during the day on Thursday. Thereafter, dry and cool high pressure
will dominate our weather through Sunday morning. Weak southerly
flow with limited moisture will return to the area Sunday and
Monday as another cold front approaches from the west.
Near term /through Thursday/...
as of 635 PM wednesday: a Wind Advisory remains in effect for
portions of the NC mountains tonight and continuing through 7 am
As another shortwave trough/weak clipper system propagates
southeastward through the Ohio Valley tonight, another dry cold
front will make it's way towards the Carolinas. Expect a gradual
increase of high clouds to begin this evening as temperatures dip
into the lower 30's overnight (mid to upper 20's across the NC
mountains), slightly warmer than last night due to weak warm air advection. Winds
will increase across the Appalachians tonight as the pressure
gradient tightens ahead of an approaching dry cold front, with gusts
across the higher terrain of the NC mountains reaching wind
criteria. As mentioned above, a Wind Advisory remains in effect for
these areas tonight through Thursday morning.
Behind the front, northwest flow/cold air advection returns and with limited low-
level moisture, could not entirely rule out brief snow flurries
Thursday morning across the northern tier of the NC mountains right
along the Tennessee/NC border. Otherwise, expect another quiet day as the
cold front slows down and nearly stalls just south of the area
across NC/SC. Despite the passage of the cold front, downsloping
will allow afternoon high temperatures to climb into the low to mid
50's across the upstate and Piedmont, though cooler into the 40's
across the Appalachians.
Short term /Thursday night through Saturday/...
as of 100 PM EDT wednesday: the short term fcst period kicks off
on Thursday evening amidst zonal 500 mb flow, while at the surface a
dry cold front settles in from the west/northwest. High pressure
behind the front will push east into Friday, setting up over the
Delmarva by daybreak. With that, expecting dry/cool conditions
to return Friday amidst partly/mostly cloudy skies early on,
gradually sct'ing out into the day. Meanwhile a northern stream
wave will work through the Great Lakes region, aiding erosion of the
aforementioned Delmarva ridge. By daybreak Saturday the trof axis
associated with the northern wave will have passed allowing for a
gradual trend of rising heights aloft, and surface high pressure
development across the southeast states. Therefore expecting dry,
sunny, and thus slightly warmer conditions on Saturday to round
out the period.
Long term /Saturday night through Wednesday/...
as of 145 PM EST wednesday: the extended fcst picks up at 00z on
Sunday with the upper pattern flattening out as upper ridging
builds to our south. As we move into Monday, upper ridging persists
over the region as an embedded southern stream 500 mb trof digs down
across the southwest and moves eastward. The European model (ecmwf) continues to be
more progressive with this system and brings it to our doorstep by
late Monday/early tues, while the other long-range models are about
18 to 24 hrs slower. Either way, the trof axis should be passing
over the fcst area by 00z Wed, with the pattern amplifying again
later on Wed. At the sfc, the pattern will remain dynamic thru the
period with quite a bit of uncertainty remaining wrt the pattern
evolution. High pressure will be centered over the area at the
start of the period early Sunday, and slide off the coast later
in the day. Beyond this point, the pattern evolution remains fairly
uncertain as each model has a different scenario wrt exactly where
and when the next sfc low will spin up to our west. They generally
agree that the next cold front will approach the County warning forecast area late Sunday
and move thru the area by late Monday/early Tuesday. The models
do agree that by the end of the period on Wed, drying high pressure
will be overspreading the region again.
Aviation /00z Thursday through Monday/...
at kclt and elsewhere: expect VFR through the taf period, but MVFR
will be possible overnight at kavl. With high pressure southwest of
the Carolinas, expect nearly clear skies with few/scattered cirrus
overnight as a dry cold front pushes through the Carolinas early
Thursday morning. The exception will be kavl where northwest flow and low
level moisture may push low VFR and possibly MVFR clouds up the
valley to the airfield after midnight. Any low clouds would linger
through the morning dissipating for the afternoon. Mainly high clouds
continue through the day elsewhere. Southwest winds around 10 kts
will continue this evening with low end gusts possible at kgsp/kmgu.
Winds diminish toward morning and turn west-northwest at kclt. Winds turn NE at
kclt Thursday evening with low VFR clouds possible in the developing
weak low level moisture and isentropic lift.
Outlook: potential for short-lived restrictions on Sunday with rain
showers. Otherwise expect VFR as a series of dry cold fronts move
through the area.
15-21z 21-03z 03-09z 09-12z
kclt high 81% high 82% Med 68% low 56%
kgsp Med 70% Med 75% high 83% Med 64%
kavl high 94% high 85% Med 70% high 87%
khky high 100% high 83% Med 66% high 100%
kgmu Med 76% high 86% high 85% Med 63%
kand Med 76% Med 65% high 90% Med 61%
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:
NC...Wind Advisory until 7 am EST Thursday for ncz033-048>052-058-