Scientific Forecaster Discussion
fxus62 kgsp 171143
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
643 am EST sun Nov 17 2019
a deep low pressure system will lift away from the Carolina coast
today. A couple of weak cold fronts will move through the area
Monday and Tuesday but temperatures will gradually warm Wednesday
and Thursday ahead of the next cold front expected late in the week.
Near term /through tonight/...
as of 640 am: not much change for this update. Updated sky and temps
to line up with obs this morning.
Otherwise, a coastal low will continue to slowly drift east off the
Carolina coast today, as a shortwave upper ridge builds in ahead of
an approaching deep trough to our west. Moist northeasterly low-level flow is
maintaining/expanding a stratocu deck, and it may be stubborn to
scatter out due to a fairly strong inversion in the 850-700 mb
layer. The NAM is much more bullish on this cloud cover (and so far
is the closest to reality). So have blended in the NAM and keep a
little more cloud cover today, especially across the south and
eastern zones. This, in combination with ongoing low-level caa,
should keep Max temps below normal today, especially east.
Fortunately, the pressure gradient is relaxing with the departing
low, so it shouldn't be as breezy as yesterday.
Tonight, a deep 500 mb trough will enter the Ohio/Tennessee valleys and pivot
into a negative tilt. This will provide strong mid to upper level
forcing atop the forecast area. The thinking over the last few days
has been for this wave to have little moisture to work with.
Overall, model trends are for a little more moisture and possibly
some light precip being able to break out late tonight. The 00z NAM
looks overdone, but has some support from the sref and European model (ecmwf).
Meanwhile, the GFS is still dry. So have introduced a slight chc of
light rain across most of the area (best chances will be along and
south of I-85). Even with this trend, I think most people will see a
trace of precip, if anything. Temps were bumped up tonight a
category or so, due to the expected increase in cloud cover (lows
near to slightly above normal).
Short term /Monday through Tuesday night/...
as of 225 am EST sunday: the guidance continues to differ with the
strength, location, and resulting precip associated with two short
waves rotating through the longwave trough over the eastern Continental U.S..
the NAM has trended toward the ECMWF, which has been consistent with
its last three runs, of bringing some light showers across the area
Monday morning. The GFS is dry while the sref has some precip.
Therefore, have added slight chance pop to the southern and eastern
sections of the County warning forecast area Monday. Dry conditions return Monday night as
the first short wave moves east. Some of the guidance shows light
precip Tuesday with the second short wave, however they continue to
differ from run to run. Have kept the forecast dry for now until
some consistency develops. Highs will be around 5 degrees below
normal both days, with lows a few degrees below normal.
Long term /Wednesday through Saturday/...
as of 245 am EST sunday: guidance in good agreement early as short
wave ridge moves over on Wednesday keeping a dry forecast in place
and temps near normal.
The guidance is now trending toward better agreement for the rest of
period. Zonal flow develops Thursday as a northern stream short wave
moves into the upper Midwest. The GFS is trending toward the European model (ecmwf)
and not phasing this wave with an upper low over The Four Corners
region. That said, the GFS is still faster than the European model (ecmwf) in moving
the northern stream short wave east across the Great Lakes into
Quebec. The GFS is also faster moving the southwestern upper low
into the area by Saturday. The European model (ecmwf) shows a similar trend but 12 to
24 hours slower. At the surface, the cold front associated with
these systems moves toward the area Thursday and into the area
Friday. The GFS brings the trailing surface low into the area
Saturday with Little Break between the initial frontal precip and
precip with the low. The European model (ecmwf) shows a break in the precip Friday
night and a slower onset Saturday as the trailing low moves slower.
As usual, went with a model blend due to these differences. This
limits chance pop to mainly the mountains late Thursday into Friday
and the western County warning forecast area on Saturday. Slight chance pop is featured
Temps go above normal Thursday, remain nearly steady Friday, then
drop to a little below normal Saturday.
Aviation /12z Sunday through Thursday/...
for kclt and elsewhere: not much change for the 12z tafs. A coastal
low will slowly drift further east off the Carolina coast today, but
lingering low-VFR cigs expected thru the morning. Guidance is mixed
on how much dry air filters in from the north this aftn, but
overall, expect most of the cigs to scatter out today. An increase
in low clouds is expected early Monday morning ahead of an
approaching cold front. Depending on how much moisture there is to
work with, spotty light rain may develop overnight, but confidence
is low. Otherwise, NE winds should remain gusty thru late morning at
kclt, then become light this aftn and somewhat variable this evening.
Outlook: brief low cigs possible early Monday with the passage of a
mainly dry front. Then dry high pressure dominates the region for
most of the work week, resulting in VFR conditions.
11-17z 17-23z 23-05z 05-06z
kclt high 100% high 91% high 91% high 100%
kgsp high 100% high 100% high 95% high 95%
kavl high 100% high 100% high 100% high 95%
khky high 100% high 91% high 95% high 95%
kgmu high 100% high 100% high 95% high 95%
kand high 100% high 100% high 95% high 95%
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: