Scientific Forecaster Discussion
fxus62 kgsp 151136
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
636 am EST sun Dec 15 2019
dry high pressure will remain over the region, before a moist cold
front crosses the area from the west late Monday into Tuesday.
Cooler Canadian high pressure will build in Wednesday and persist
through the end of the work week.
Near term /through tonight/...
as of 735 am: some clouds, valley fog, and gusty winds lingering
across the mountains early this morning will dissipate through the
Heights slowly rise across the area today as high pressure builds in
from the west. Expect the lower clouds across the mountains to
dissipate through the morning as cirrus increases and thickens.
Gusty northwest winds across the higher elevations will diminish
through the day as well with light southwesterly winds elsewhere.
Highs will be around 5 degrees above normal.
Heights continue to rise tonight as a weak ridge builds off the
Atlantic coast and a trough develops over the MS River Valley.
Surface high pressure moves off shore overnight as a warm front
develops over the Tennessee River valley. An increasingly moist,
southwesterly low level flow develops during bringing increasing
low level clouds across the area. The moisture is shallow and the
isentropic lift weak; however, there may be enough mechanical,
upslope lift for some patchy rain to develop across the southwestern
mountains and along the Blue Ridge Escarpment of the NC/SC/GA
borders. While southwesterly winds will increase across the area,
they will remain generally light for all but the highest ridges west
of the French Broad valley, as usual for a southerly, warm advection
pattern. Gusts should remain below advisory levels for all but
possibly the highest ridges of the smokies. Lows will be around 10
degrees above normal.
Short term /Monday through Tuesday night/...
as of 145 am EST sunday: an active weather pattern is still in the
works over the short term period. Good agreement is had in the
latest model runs with a broad h5 trof deepening across the
Midwest...while a wavy frontal system sets up over the Tennessee/Ohio
valleys by 12z Mon. Due to the positive alignment of the upper
trof...the stronger deep forcing will remain west and north of the
forecast area as the sfc front crosses the area thru Tue evening. Cross
sections show elevated Omega ahead of the fropa...which is a notable
weakening trend from previous guidance. There looks to be a low-end
elevated cape potential on Tue just ahead of the llvl convg
zone...while deep shear remains high and hodos become right-turning.
So...organized qlcs lines are not out of the question by mid-morning
into the afternoon mainly along and south of the i85 corridor.
The SW NC mtns will see the brunt of the rainfall where localized
areas could receive up to 2 inches Mon night...which may lead to
minor Hydro issues along small streams and low-lying areas. Winds
still look to be moderately strong over the mtns abv 3500 ft as a
50 kt h85 jet develops aft midnight. A wind adv may be needed for
these areas as widespread damaging winds are not expected to warrant
a High Wind Warning attm. This windy scenario will continue to be
monitored over the next few shifts. Behind the front...upslope northwest
flow -snsh will develop across the NC mtns...however with shallow
and waning moisture...accums will be low end-end and likely below
With continued SW/ly flow ahead of the front and W/ly downslope
winds Post frontal...Max temps will reach the m60s each afternoon
over the non/mtns. The mtn valleys will be warm Mon with readings
reaching the l60s Mon and still abv normal yet cooler in the m50s
on Tue. Warm sector cloudiness and llvl mixing will help hold mins
abt 20 degrees abv normal Mon night...then a 20 degree drop to
normal levels Tue night as a cp airmass mixes into the forecast area.
Long term /Wednesday through Saturday/...
as of 230 am EST sunday: upper level heights begin to rise as a
ridge axis develops west of the fcst area Wed. A stg subs zone will
encompass the region beginning Wed afternoon...which will allow a
1028 mb sfc high to transit the se/rn states into Fri. This setup
will return clearing skies and cooler Max/min temps...altho near or
just below normal levels each day. By Fri night...a developing h5
trof will dig across the ern Continental U.S. Which will be a weather maker for
the forecast area into the weekend. Much uncertainty exists during this time
frame as the GFS and European model (ecmwf) models are at odds with the details of
the trof config. The GFS is developing a closed low within the trof
and diving it across Georgia/SC and off the atl coast thru Sat...while
the European model (ecmwf) keeps a faster non/closed trof axis crossing the area with
limited coastal sfc low development. The GFS scenario would bring a
decent amt of wintry precip to the forecast area as colder air would have more
time to be advected south as the low deepens off the coast. The
latest European model (ecmwf) on the other hand keeps the better moisture axis over
the ern zones with a limited freezing sfc-layer potential. Its
interesting that the 00z European model (ecmwf) has trended more inline with the
colder and moister GFS soln...however this system will be monitored
over the upcoming week and much can change with the sensible weather
fcst. So for now...have a low-end chance sn or -ra/sn mix over the
northern zones Fri night with limited/nil snow accums.
Aviation /12z Sunday through Thursday/...
at kclt and elsewhere: VFR at all taf sites into the evening. Low
VFR clouds across the mountains, and some valley fog, will dissipate
this morning leaving increasing and thickening cirrus across the
area through the afternoon. Generally SW wind continue through the
day, west-northwest at kavl. Mid and low VFR clouds will move in from the west
and/or develop over the area this evening as a moist south to SW low
level flow develops. Winds turn S to SW, even at kavl, overnight as
well. With relatively strong winds developing at ridge top level,
low level wind shear is likely to develop at kavl. MVFR cigs and vsby develops at
khky, kavl, and kand by morning. Low VFR at kgsp/kgmu. Low VFR holds
off until after daybreak at kclt.
Outlook: moisture increases across the area ahead of the next cold
front, which will cross the region Monday night into Tuesday. The
front will bring a round of rain showers, with cig/vis restrictions
likely. Drier air and stronger high pressure will set up by midweek.
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 89%
kavl high 100% high 100% high 100% high 89%
khky high 100% high 100% high 100% high 100%
kgmu high 100% high 100% high 100% high 94%
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: