Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
634 am EST sun Jan 25 2015
high pressure will build back into the region today...before another
low pressure area and trailing upper level disturbance move through
Monday and Tuesday. High pressure returns during the latter half of
Near term /through tonight/...
as of 630 am...other than some patchy thin cirrus sweeping across
northern NC...skies are clear across the forecast area this morning.
By the end of the morning...southerly winds will begin to increase
and temperatures will warm to the middle/upper 40s across much of the area.
A rather pleasant day is in store for the region...as a S/SW flow
will become established in the low levels. Thickness values beneath
a temporarily flattening long wave trough will support maxes around
5 degrees above climatology this afternoon under sunny/mostly sunny skies.
The weather situation will then change rather abruptly this
evening...as potent upper speed maximum...currently seen in water vapor
imagery digging south across the Central High plains...dives into
the southeast Continental U.S.. this will bring a rather healthy area of middle-
level forcing into the area...with some degree of low level
convergence and isentropic lift into the tenn valley and southern
Appalachians in association with attendant cold front this evening.
This supports likely to categorical probability of precipitation across the mountains during this
time. Miller-b scenario of weakening Ohio Valley surface low...and
developing coastal low pressure will then disrupt low level forcing
patterns such that probability of precipitation will decrease dramatically toward the
Piedmont. However...some light NC Piedmont precipitation may develop in
association with coastal cyclogenesis...although probability of precipitation will be Middle-
Range chance at best.
With a rather respectable /cross-hair/ signature depicted in model
cross-sections...thermal profiles will be supportive of snow across
the mountains. However...it appears this will primarily be for
elevations above 3000 feet or so...with the lower elevations maybe
seeing a brief changeover as developing cold advection brings the
snow levels down to the valley floors. Having said that...this
appears to be quite a low quantitative precipitation forecast event for the area. In fact...the only
areas in which advisory level snow is being forecast through 12z
Monday is across the high elevations of the smokies...with most
other areas expected to see little more than an inch. After
collaborating with neighboring weather forecast offices...this is a small enough area...
and timing is such that we can wait another forecast cycle before
pulling the trigger on any advisories. Continuing the severe weather potential statement mention
should suffice for now.
Short term /Monday through Tuesday night/...
at 230 am EST Sunday...on Monday morning an upper trough will be
over eastern North America...with a ridge over the west. A strong
shortwave will be crossing Georgia and the Carolinas on Monday. This
shortwave moves off the coast by Monday evening. Channeled vorticity
behind from the northwest behind the departing shortwave persists into the
southern Appalachians through Tuesday night.
At the surface...a cold front will be moving off the Carolina coast
on Monday morning...while a surface low will be over the central
Appalachians. Moisture associated with the weakening appalachian low
will slowly move east across our area during the day. By late in the
day...northwest surface flow sets up over our area behind the departing
cold front and an associated deepening coastal low. This will aid in
drying our the Lee of the mountains on Monday night. Meanwhile...a northwest
flow snow event will setup in the NC mountains bordering Tennessee that
will persist into Tuesday night. Temperatures will run near normal
on Monday and Monday night...cooling slightly for Tuesday and
Long term /Wednesday through Saturday/...
at 230 am EST Sunday...on Wednesday morning and upper trough will be
off the East Coast....while a ridge will be over the plains. As the
trough deamplifies and progresses further on Thursday...a low
amplitude ridge reaches the East Coast...and a low amplitude trough
reaches the MS River Valley. This trough amplifies and progresses to
the eastern USA by Friday...though the models differ slightly on
placement of its axis. The models show a broadening trough by
Saturday as upper level energy moves from Canada to the northern US
plains...and have a nearly zonal flow in the base of the trough over
the Gulf states.
At the surface...Wednesday features high pressure moving from the Ohio
and Tennessee River valleys across the central and southern Appalachians.
By Thursday this high stretches along the East Coast....while a cold
front crosses the MS River Valley. The front moves quickly through
our area late Thursday...and off the East Coast by Friday morning...
followed by another round of northwest upslope flow snow over the NC
mountains. Another surface high moves over the mountains by early
Saturday...ending the mountain snow event. Temperatures will warm
from near normal on Wednesday...to slightly above normal on
Thursday...then will cool to slightly below normal by Saturday.
Aviation /12z Sunday through Thursday/...
at kclt and elsewhere...VFR conditions expected through the next 18
hours or so. Winds will increase out of the south at 5-10 kts by
afternoon...ahead of the next cold front/upper air disturbance. VFR
ceilings between 050-100 are expected to overspread the area quickly
during the evening in advance of this system. Precipitation chances will
also increase by around 06z...mainly across the mountains...and a -ra
mention has been introduced at kavl. Rain chances are non-zero...
but much lower at other terminals. Increasing moisture is expected
to result in development of MVFR ceilings between 06z and 12z at most
terminals. Some guidance is extremely pessimistic during this
time...featuring widespread IFR/LIFR ceilings. Although I wouldn/T rule
this out in areas that see at least a couple of hours of rain...
confidence in that is very low at this time...so have opted to hold
conditions at the MVFR level for the time being.
Outlook...a series of clipper systems will bring periodic chances
for snow showers...mainly to the mountains through the week. Most of
these snow showers will remain west and north of kavl...but brief
periods of restrictions and snow showers cannot be ruled out there.
Otherwise...mainly VFR conditions are expected.
11-17z 17-23z 23-05z 05-06z
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% medium 66%
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)