Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
235 am EST Thursday Dec 25 2014
high pressure will arrive from the west today and linger into
Saturday. A pair of cold fronts will approach the area on
Sunday...crossing the area Monday. Gusty winds will follow the
fronts on Tuesday...decreasing on Wednesday.
Near term /through tonight/...
as of 210 am EST...the passing surface cold front has moved east to the
coastal plain of the Carolinas early this morning...while the
deamplifying upper trough axis remains just west of the
Appalachians. Steady drying continues for most areas...with the
western mountains the main exception in moist westerly upslope flow.
Forcing will maximize circa 09z this morning...with brief upper
divergence along The Spine of the southern Appalachians...passing middle
level DPVA with the wave...and the apex of the moist westerly
upslope flow around that time. Profiles will support rain showers
mixing over to snow showers...with some light snow accumulations
possible along the higher ridge tops through daybreak. No advisory
level accums are expected.
Otherwise...anticipate flat upper ridging through the day as the
deamplifying trough passes to the east. A surface Lee trough should
develop and keep winds SW through the day...at least across the southern
tier of the forecast area. The combination of good insolation from
middle morning Onward...a light downsloping westerly 850 mb flow...and
the Lee troughing will contribute to maxes one to two categories
above normal in most locations east of the mountains the surface high
pressure center will then build overhead tonight...with seasonable
mins in the 20s mountains to 30s east.
Short term /Friday through Saturday/...
at 230 am EST Thursday...on Friday morning an upper ridge will be
over the eastern USA....while a trough will be over the west with a
closed low over the central rockies. By Saturday the low opens up
and fills...and the western trough takes on a positive tilts from
the northern plains to the southern rockies...while the eastern ridge
axis moves off the coast. The result is a longer wavelength and
decreasing amplitude into Saturday night.
A dry surface ridge will be centered over the Carolinas on Friday
morning. The ridge center moves off the NC coast by Friday
evening...while Gulf moisture starts moving north up the MS River
Valley in advance of a front in the Southern Plains. By Saturday
morning Gulf moisture overspreads the Gulf states...and by late in
the day it reaches the upper Savannah River valley and southern
Appalachians. Isentropic upglide over a Gulf warm front will result
in widespread moisture across our area...though lift and resultant
precipitation will be rather limited.
Long term /Saturday night through Wednesday/...
at 230 am EST Thursday...on Sunday morning an upper high centered
over the Caribbean will extend north off the East Coast...while a
high amplitude trough will be over the plains. By Monday...the ridge
progresses slightly...while the trough upstream retrogresses
slightly as upper level energy dives south over The Rockies...
resulting in a lower amplitude pattern that persists into Tuesday.
An upper low closes off int the southwest by Wednesday...while
nearly zonal flow extends downstream to the East Coast.
A cold front will slowly cross the western Carolinas and NE Georgia from
the west on Sunday and Sunday night. Gulf inflow ahead of this
boundary will be limited...but modest upslope flow and isentropic
upglide will support widespread...generally light precipitation. By
Monday morning the front will be exiting our area to the east...
while another cold front approaches from the northwest. The second front
moves through during the day...followed by some moist northwest upslope
flow into the mountains that will last into Wednesday. Although
cold advection will set up...it appears that critical thickness
values may be lacking early on...and rain showers will be the
predominant precipitation type until early Wednesday. Temperatures
will run above normal ahead of the front...falling to near normal
behind the fronts at midweek.
Aviation /08z Thursday through Monday/...
at kclt...expect mainly broken altocumulus and cirrus for the early
part of the taf period...until the upper jet streak can clear to the
east by middle morning. Patchy lingering stratus at MVFR levels could
flirt with the airfield for an hour or two early this morning before
drying up in the westerly flow. Otherwise...surface winds should remain
just north of west through the period around 10 knots in the Post frontal passage
airmass before becoming light this evening as surface high pressure
build in from the west. There is some potential for Lee troughing to
toggle winds west-southwest today...but it appears the best troughing will be
closer to the SC foothills and not affect kclt to any large degree.
Elsewhere...lingering low clouds scattered at issuance time at
khky...which means that foothills ceilings going forward should be
mainly altocumulus and cirrus until the upper jet streak clears east
by middle morning. The main question mark is kavl...where low level
moisture on westerly upslope flow could push up the valley to
approach the airfield through the early morning hours. Mainly scattered
MVFR level clouds will be featured for the pre/dawn hours before the
low level moisture dries up. Expect northwest winds at the NC taf sites and
mainly west-southwest winds at the SC taf sites with Lee troughing developing.
Winds will go light this evening as high pressure builds overhead.
Outlook...dry high pressure will persist late tonight through
Friday. Another cold front will arrive from the northwest over the weekend
and may stall over the mountains that might permit restrictions to
develop by Sunday morning...perhaps continuing through the middle of
07-13z 13-19z 19-01z 01-06z
kclt high 95% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 92% high 91% high 100% high 100%
khky medium 78% high 100% high 100% high 93%
kgmu high 100% high 100% high 100% high 100%
kand medium 74% 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)