Scientific Forecaster Discussion
fxus62 kgsp 190003
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
703 PM EST Mon Nov 18 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 Tuesday/...
as of 655 pm: main update for the 00z taf issuance along with
minor adjustments made to temperatures/sky cover, once again, to
coincide with latest trends, as the rest of the near term
forecast remains on track. Conditions remain quiet this evening,
with plenty of low cloud cover in place in and around the I-77
corridor, and current temperatures across the area in the mid to
upper 40s to lower 50s.
Previous discussion: with the back edge of the precip associated
with negatively tilted short wave trough well off to the northeast,
conditions are expected to remain dry through the rest of the near
term forecast period. Skies will continue to gradually clear from
the west, but clearing has struggled to reach the I-77 corridor
before sunset, and this lack of mixing/insolation along with weak-at-
best dry air advection is expected to set the stage for a low
stratus/fog event across 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 /Tuesday night 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 /00z Tuesday through Saturday/...
for kclt and elsewhere: a mix of VFR and MVFR due to low cigs
prevails at the taf sites this evening. With available low level
moisture in place, anticipate flight restrictions to deteriorate to
MVFR/possible IFR at kgsp, kgmu, and kand, with IFR/possible LIFR at
kclt and khky tonight into the early morning hours, due to low cigs
and patchy fog. Per latest guidance, expect conditions to gradually
improve through Tuesday morning, with VFR expected by the late
morning hours, continuing through the remainder of the valid taf
period. Light and variable winds overnight will become light and
northerly early Tuesday morning, to west-southwest at or below 5 kts by
early afternoon (kavl will remain wnw).
Outlook: expect Mountain Valley fog during the morning hours through
Thursday, along with increasing precipitation chances and flight
restrictions possible on Friday. Otherwise expect VFR.
00-06z 06-12z 12-18z 18-00z
kclt high 86% low 54% Med 75% high 95%
kgsp high 85% Med 60% high 82% high 100%
kavl high 100% high 100% high 100% high 100%
khky high 81% Med 60% Med 74% high 100%
kgmu high 89% Med 63% high 80% high 100%
kand high 100% Med 76% high 83% 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: