Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1251 PM EST Thursday Nov 26 2015
dry high pressure will prevail through the first half of the weekend
before a cold front approaches from the north and west Saturday
night into Sunday. Cool and wet high pressure will prevail on Monday
before another frontal system slides in on Tuesday.
Near term /through Friday/...
as of 1245 PM EST...1042 mb high pressure over Virginia will remain nosed
SW through the western Carolinas and NE Georgia through Friday. The only real
moisture to be found in profiles around the area will be in the
surface to 850 mb layer...and southeast flow in this layer should permit
the low level moisture to pool mainly along the eastern slopes of the
southern Appalachians tonight. The potential for any light quantitative precipitation forecast will be
greatest in the upslope zones during the late evening and early
morning hours...but with nothing more than isolated pop for light rain.
Mins should run several categories warmer on Friday morning given the
expected clouds and recovering boundary layer temperatures.
A 500 mb ridge axis will remain stretched from the Gulf Coast to the
forecast area through the near term...but with minor height falls
and a shortwave arriving from the west over the southern
Appalachians late Friday. This feature will have little to no
moisture to work with so expect little more than lingering scattered
cirrus. At lower levels...veering of the 850 mb flow will reduce the
upslope moisture through the day on Friday. The resulting decent
insolation should permit maxes to reach the middle to upper 60s most
locations east of the mountains...with plenty of 60s in the mountain
Short term /Friday night through Saturday night/...
as of 200 am EST Thursday...the short range forecast period initializes
on Friday morning amidst a sharp 500 mb ridge parked over the southeast
states with its center out over the central Gulf...while a closed
upper low rotates over The Four Corners and another trough axis
dives southeast through the Great Lakes. At the surface...the
parent high centered off the Canadian Maritimes will be in control
as it stretches along the eastern Seaboard...while a cold front
approaches from the west. Continued model runs have consistently
been slowing the progression of the pattern through the weekend.
Thus...expecting the above mentioned maritime high to eject out
to sea with the southern tier breaking off over the Middle Atlantic
States...to include northeast Georgia and the western Carolinas through
the day on Friday. Likely aided by ridging aloft...this feature
looks to persist and possibly aid in slowing the progression
of the frontal intrusion...which now looks to hold off until
sometime Sunday morning as it back doors into the Interstate 40
corridor per the GFS/NAM while the European model (ecmwf) is nearly 12 hours slower.
All in all the front looks rather dry thus will favor the lower
end of guidance.
As for the forecast...the short term will remain dry through the vast
majority of the period before probability of precipitation ramp up to slight/chance levels
over the mountains/fthills as the front approaches into Sunday morning.
Skies will be partly cloudy on Friday and Saturday as sufficient
llv moisture persists...with sky cover increasing Saturday night
ahead of the front. Temperatures through the short term will
remain a few degrees above normal.
Long term /Sunday through Wednesday/...
as of 215 am EST Thursday...the medium range forecast period initializes
on Sunday morning amidst some model discrepancy as it pertains to
the arrival of a back door cold front. Although faster with the
latest run...the European model (ecmwf) is slower and or less aggressive than the
GFS...and to some degree the CMC as it pertains to frontal intrusion
into western NC on Sunday. The former tends to hold off until
sometime early afternoon Sunday...while the later two allow for the
boundary to reach near the Interstate 40 corridor by early morning.
Nevertheless...guidance does agree that the front will be fairly
dry...and thermal profiles too warm for any significant concerns.
High pressure will slide in behind the front over New England by
late day Monday regardless of model choice...thereby establishing a
new cad regime in the Lee of the Apps. Meanwhile...an upper vortex
over The Four Corners will be on the move and thus initiating
surface cyclogensis over the Central Plains with another cold
front trailing behind. The ejection of the upper trough/low and
the progression of the consequent surface cyclone will yield
southerly veered llv flow atop the a fore mentioned wedge and
thus upglide...with upsloping also possible along the southern
Escarpment on Monday afternoon/evening. The front associated with
said surface low looks to push through sometime on Tuesday night
with broad high pressure prevailing after that time.
The forecast features middle/high chance probability of precipitation over the high terrain
with slight chances east at forecast initialization. High terrain
probability of precipitation increase to low end likely levels into Monday...while the
Piedmont remains at middle chance levels. The entire forecast dries
out behind this system leading into Wednesday afternoon/evening.
Temperatures through period will generally remain just below climatology
levels given the various rounds of precipitation and cloudiness.
Aviation /18z Thursday through Tuesday/...
at kclt and elsewhere...surface high pressure will remain draped
over the area through the period...with persistent east to southeast flow in
the surface to 850 mb layer bringing some Atlantic moisture into the
picture. The MOS/models have been way too aggressive with low clouds
in most areas recently...but boundary layer relative humidity recovery will permit
a better chance of restrictions early Friday morning. Will feature a
window of MVFR ceilings and visibility most areas despite the more dire MOS
forecasts of IFR to LIFR conditions. Expect NE surface winds less than
10 knots through the period...except light southeast at kavl.
Outlook...generally dry high pressure will persist into the early
weekend...but with moisture and associated restrictions possibly
returning with a back door cold front Sunday into Monday. The
moisture and rain chances will increase into Tuesday.
18-24z 00-06z 06-12z 12-18z
kclt high 99% high 100% high 84% high 84%
kgsp high 100% high 84% high 86% high 88%
kavl medium 74% medium 77% high 87% high 84%
khky high 84% high 83% high 92% high 90%
kgmu high 100% high 87% high 80% high 86%
kand high 100% high 83% high 82% medium 74%
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)