Scientific Forecaster Discussion
fxus62 kgsp 201547
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1047 am EST Wed Nov 20 2019
dry high pressure builds into the region today and lingers through
Thursday. A cold front with rain showers will approach the area from
the west on Friday and pass through on Saturday. Cool high pressure
returns Sunday and continues through early next week.
Near term /through tonight/...
as of 1040 am: northwest flow stratocu will slowly dissipate into early
afternoon, with sunny skies expected in all areas by mid-afternoon.
Windy to breezy conditions across the mountains will diminish
through the day as well. Many locations will see plenty of sunshine
today with highs very close to normal, except across the far western
mountains, where morning clouds will keep be maxes a few degrees
Clear skies expected tonight with light winds but Mountain Valley
fog is likely, especially in the little Tennessee Valley. Patchy fog is
possible elsewhere. Lows should be near to slightly below normal.
Short term /Thursday through Friday night/...
as of 245 am wednesday: dry and seasonably mild conditions continue
on Thursday, as sfc high pressure crosses the region under an upper
level ridge. The ridge and sfc high shift east on Friday, as a
strong shortwave trough crosses the Great Lakes. A southern stream
upper low will enter the Central Plains and should induce a sfc wave
along a frontal zone over the arklatex region. Southwesterly warm air advection flow at 850
mb will ramp up ahead of the front across the forecast area late
Thursday thru Friday, and should start producing a few showers in
the usual upslope areas. The Piedmont will see an increase in
clouds, but should be generally dry until possibly late in the day
Friday, with some scattered showers developing within a warm sector
air mass. Temps will be slightly above normal for highs, and well
above normal for lows with the increasing clouds.
Long term /Saturday through Tuesday/...
as of 300 am wednesday: a southern stream trough and associated low
pressure system is progged to cross the forecast area on Saturday.
Models have been gradually coming into better agreement on the
timing and details. As the center of the low tracks NE across the
Ohio Valley and into the central Appalachians, it will push a cold
front thru the forecast area. The models hint at a little SBCAPE
along the front, but still looks mainly confined to the Gulf Coast.
If we can manage to get a few hundred j/kg of cape, there certainly
will be enough shear and forcing to support some severe weather. We
will continue to monitor trends, but for now no thunder mention for
Saturday will be carried. Temps should be above normal on Saturday.
Most of the moisture and precip pulls out of the area before the
colder air arrives, resulting in just a brief changeover in the
highest peaks late Saturday night. The 00z GFS has a potent compact
vort Max dive into the longwave trough, crossing the southern
Appalachians Sunday aftn/eve. This feature could be accompanied by a
quick shot of showers (with possibly snow in the high elevations).
But none of the other guidance has this, so was thrown out of this
fcst. Otherwise, cool high pressure should build in, bringing temps
back down to near or slightly below normal for Sunday and Monday.
The overall pattern stays progressive, and the next storm system may
be knocking on our door as we head into Tuesday. The GFS and European model (ecmwf)
diverge on the timing and evolution of this system. The previous ec
actually lined up well, but the New Run has come in faster and
weaker with the overall low pres system. Have pops starting to ramp
up late Tuesday, peaking Tuesday night in the chc to likely range.
Thicknesses rebound such that the precip is expected to be all rain.
Aviation /16z Wednesday through Sunday/...
for kclt and elsewhere: VFR currently at all taf sites but with
low VFR cigs at kavl. The clouds will slowly dissipate through the
morning with cirrus for the afternoon. Patchy fog at the non-taf
sites will dissipate quickly after daybreak. Generally light north to northwest
winds continue through the day. North-northwest wind with low end gusts expected
at kavl. Winds drop off all areas this evening with Mountain Valley
fog developing overnight.
Outlook: increasing precipitation chances and flight restrictions
with a cold front on Friday and Saturday. VFR Sunday.
15-21z 21-03z 03-09z 09-12z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 98% high 100% high 100% high 100%
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: