Scientific Forecaster Discussion
fxus62 kgsp 212049
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
449 PM EDT Mon Oct 21 2019
rain will be widespread and perhaps heavy at times ahead of a cold
front which will cross Tennessee tonight and our area on Tuesday.
Cool and dry high pressure will settle in for Wednesday and Thursday
as an unsettled weather pattern returns for the weekend and to
start next week.
Near term /through Tuesday/...
as of 445 PM edt: sky cover has been boosted slightly late this
afternoon as earlier gaps in the sky cover filled in very quickly
with heating. Otherwise, the forecast remains on track, with a short
wave rotating around an upper low and pushing a cold front into the
area tonight. The short wave and cold front will cross the area
Tuesday. Guidance shows a wave forming along the front and moving
northward along it as it crosses the area. There will be some strong
forcing with the system. Weak surface based instability develops as
well. Bulk shear and helicity increase as the system moves through.
However, it looks like there will be little overlap of these
features. Kept isolated thunder in the forecast given the forcing
and instability, but the chance of any severe storms is low. Of
course, will have to keep an eye on any strong convection that does
develop. Precip should taper off quickly in the afternoon as the
front and wave push eastward. Low end gusts should develop along and
behind the front, but remain well below advisory levels. Lows
tonight will be around 15 degrees above normal. Highs Tuesday should
be near normal across the mountains and around 5 degrees above
Short term /Tuesday night through Thursday/...
as of 210 PM EDT monday: quiet weather is on tap for the short term.
The longwave trough responsible for pushing the cold front through
the area will rapidly lift northeast away from the region through
Wednesday with broad southwest flow aloft taking over in its wake.
Breezy west to northwest winds behind the trough will continue to
usher in cooler air with a 1025 mb surface high building into the
region late Wednesday and lingering into Thursday. This will support
sunny skies with winds becoming light by Wednesday evening. Winds
will probably be just strong enough to preclude frost development in
all but possibly the most sheltered mountain valleys late Tuesday
night into early Wednesday morning. Good radiational cooling
conditions (clear skies, light winds and low dewpoints) will likely
support fairly widespread frost with isolated freeze conditions for
the mountains into the North Carolina foothills Wednesday night with
patchy frost possibly extending into the North Carolina Piedmont,
especially north of I-40. Highs Wednesday and Thursday will be near
if not slightly below normal despite sunny skies with highs in the
60s to near 70.
Long term /Thursday night through Monday/...
as of 145 PM EDT monday: starting with Thursday evening with dry
conditions as surface high pressure departs the East Coast. On the
500mb pattern Thursday night a broad trough covers the mid section
of the nation. As this trough moves east, moisture will advect up
from the Gulf of Mexico setting the stage for a prolonged period of
considerable clouds and periods of rain. Timing is quite different
between the GFS and European model (ecmwf). The GFS has the rain arriving from
Georgia very early Friday and widespread moderate to at times heavy
rain Friday night and Saturday morning. The GFS has high pressure
passing across late in the weekend as the front lingers across
Florida and moisture returning early in the week. The ec maintains
dry weather until late Saturday for the western mountains with low
pressure crossing Oklahoma Saturday night then Missouri on Sunday.
The ec has the bulk of the rain crossing Tennessee on Sunday and the
NC mountains getting good rain Sunday night. The ec keeps the
weather unsettled next week as another low pressure approaches from
the west. The bulk of that rain does not arrive until late in the
week. With vast differences in the models at least they do agree in
a general sense that our weather will be unsettled in this forecast
period. Temperatures close to seasonal normals with the warmer day
Aviation /21z Monday through Saturday/...
at kclt and elsewhere: where low clouds have eroded, bases have
filled back in quickly from heating, generally at upper-end MVFR
levels or lower-end VFR. Expect areas that are VFR will remain there
until this evening while locations with restrictions keep them.
Conditions deteriorate overnight as precip increases ahead of an
approaching cold front. MVFR cigs falling to IFR or even LIFR looks
likely, with MVFR to IFR vsby. Isolated thunderstorms and rain are expected,
especially along the front, but timing is still uncertain and chance
too low for tafs. Precip ends and restrictions slowly lift with
frontal passage during the afternoon. Generally southeast winds
through the evening, becoming SW then northwest. May be some gusts as well
with and behind the front.
Outlook: VFR conditions through Thursday as high pressure builds
into the area. The next storm system will approach the area late in
20-02z 02-08z 08-14z 14-18z
kclt high 98% high 87% high 90% Med 78%
kgsp Med 79% high 86% Med 77% high 82%
kavl high 86% Med 77% high 80% Med 79%
khky high 95% high 87% Med 70% high 81%
kgmu high 80% Med 73% high 89% Med 79%
kand high 91% high 86% high 84% Med 75%
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: