Scientific Forecaster Discussion
fxus62 kgsp 190546
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1246 am EST Tue Nov 19 2019
dry high pressure will encompass the region over the next several
days. Temperatures will gradually warm ahead of a moist cold front
expected to reach the area late in the week.
Near term /through today/...
as of 1245 am: patchy dense fog continues to spread across the area
early this morning. If conditions continue to worsen, then a dense
fog advisory will be needed. For now, have expanded the Special Weather Statement in line
with latest obs. Updated for other current conditions as well.
Previous discussion: given earlier conditions, anticipate a low
stratus/fog event the Piedmont late tonight into early Tuesday, with
at least patchy dense fog possible. Min temps are forecast to be
right around climo.
Another upper speed Max is forecast to dig into the base of the
eastern trough on Tuesday, but is expected to find limited moisture
with which to work over our forecast area. We cannot completely rule
out some sprinkles/--ra across the Piedmont during the day, but
current guidance suggests <20 pops to be the best forecast. Pops
will increase to the chance range late in the day across the far
western NC mtns, where accelerating northwest low-level flow acting on
lingering moisture could result in some upslope shower activity near
the Tennessee border. Any precip would be all-liquid except perhaps at the
highest peaks. Max temps will again be about 5 degrees below
Short term /tonight through Thursday/...
as of 2pm EST monday: short-term will be the quiet part of the
forecast, with upper wave departing eastward Tuesday night and being
replaced by a mid-level ridge by Thursday morning. A trace of
precipitation is possible in ending northwesterly flow over the
mountains Tuesday night, with a possible light dusting of snow at
the highest elevations. Otherwise, mild dry-advective pattern will
lead to the end of clouds most areas by Wednesday morning, with
clouds again increasing on Thursday in advance of the next system.
Northwesterly surface flow reduces dewpoints on Wednesday, and ends
Wednesday evening as surface high becomes centered over the area.
Upper flow is fairly progressive, and surface high moves off with
the commencement of southwesterly flow late on Thursday.
Precipitation is expected to be non-existent Wednesday and Thursday,
though dewpoints will begin to rise at the end of the period as SW
flow kicks-in ahead of leading front from next system. Clear skies
and some downslope component to the flow on Wednesday will keep the
airmass just above normal in temperature Wednesday and Thursday.
With weak surface features and surface high becoming centered over
the region on Wednesday, surface winds will be fairly light, with
some increase beginning late on Thursday.
Long term /Thursday night through Monday/...
as of 2pm EST monday: latest round of models still have a
precipitation event in the Friday-Saturday period as a major front
crosses the region preceded by a moisture surge. GFS shows dewpoints
advancing over 10 degrees from Thursday to the end of friday; with
precipitable water levels increasing an inch to around 1.3 inches in Piedmont
areas. Recent guidance has increase precipitation amounts, with a
half inch to an inch now looking possible in the Friday through.
Sunday period. GFS additionally has an axis of 2+ inches east of the
mountains, a possible, but maybe illusory feature not seen in the
ec, and which is lost upon model blending. Latest expectations of
timing (per the gfs) have front reaching the Tennessee state line area
Friday afternoon, exiting into the SC low country by Saturday
morning. Ec timing is about a half day behind the GFS. Precipitation
should follow along and behind the front with the heaviest amounts
on Saturday. Strongest winds will be just ahead of the frontal passage late on
Friday, though not too bad at 10 to 15 kts with some gusts to 20 at
higher elevations. Both main models now agree in having a period of
dry-advection behind the front, giving much reduced pops and
clearing from later Sunday through Monday. Temperatures should fall
behind the front on Sunday, with highs falling 5 to 10 degrees.
Well-defined cold front will generally give either rain or snow,
depending on surface wetbulb temperatures. Latest expectations are
for an all rain event, with the possible exception of some snow at
the highest elevations behind the front late on Saturday or early
Aviation /06z Tuesday through Saturday/...
for kclt and elsewhere: IFR to vlifr vsby and cigs have developed
across much of the area outside of the mountains early this morning.
Conditions have slightly improved in some areas and will continue to
worsen in others. Have kept conditions low for all but kavl where
conditions will be better but IFR is possible. Conditions will be
slow to improve after daybreak but VFR expected at all sites by
noon. VFR with mainly high clouds, low VFR over the mountains,
expected for the afternoon. MVFR clouds may return to the mountains
overnight. Generally VFR expected elsewhere, but patchy fog
possible. Light and variable winds expected through the period for
all but kavl where north-northwest wind continues through the period.
Outlook: expect Mountain Valley fog during the morning hours
Thursday, with VFR elsewhere. Increasing precipitation chances and
flight restrictions possible Friday and Saturday.
05-11z 11-17z 17-23z 23-00z
kclt high 100% high 100% high 83% high 100%
kgsp high 100% high 90% high 100% high 100%
kavl high 94% Med 75% high 83% high 100%
khky Med 72% Med 75% high 83% high 95%
kgmu high 100% high 90% high 94% high 100%
kand high 100% high 95% 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: