Scientific Forecaster Discussion
fxus62 kgsp 220300
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1000 PM EST Thu Nov 21 2019
a cold front with rain showers will approach the area from the west
on Friday and move through the region on Saturday. Cool high
pressure returns on Sunday through early next week.
Near term /through Friday/...
as of 945 pm: virga on regional radars has dimininished this
evening, while actual precipitation continues to fill in well to the
west as a frontal zone slips southeast toward the confluence of the
Ohio and Mississippi rivers. This slightly better moisture advancing
from the west will encroach on Tennessee border locations toward
daybreak, so will continue to advertise slight chance pops for light
showers along the far western mountains through 12z. Min temps will
be above climo under increasing mid/high level cloud cover.
The frontal boundary at the leading edge of the broad baroclinic
zone will then approach the forecast area tomorrow, but will become
increasingly zonal in its configuration. Meanwhile, cyclogenesis
will initiate across the lower miss valley, while a northern stream
cyclone moves off the New England coast. As a result, deep forcing
passes north of the forecast area, while another region of forcing
becomes increasingly focused near the area of deep south
cyclogenesis. Guidance therefore generally depicts frontal precip
becoming less organized as it approaches the southern Appalachians
Fri afternoon. Confidence in some amount of rain surviving to the
Tennessee/NC border is such that likely to low end Cat pops will be
advertised there by late day, but pops decrease sharply to the
east/southeast such that they are 20-30% southeast of the Blue
Ridge. Temps will again be above normal, especially under less thick
cloud cover/precip-free air over the Piedmont, where upper 60s
Short term /Friday night through Sunday/...
as of 1215 PM thursday: shower cvrg and magnitude is still expected
to increase commencing Friday night with the encroachment of
southern stream energy, an increase in upglide, and potential
focusing along stalled E-W oriented frontal zone. Certainly the
pattern shaping for Saturday will support widespread locally heavy
showers into the evening along and ahead of a moderately forced cold
front. It remains to be seen whether the quantitative precipitation forecast maximum sets up along
the typical favored upslope areas or along the stalled llvl frontal
zone in the Piedmont. At any rate, the sensible wx fcst will remain
pretty much the same as what I inherited categorical shower cvrg
with a heavy rain mention.
Along with the ongoing marginal day 3 excessive rain threat posted by
wpc, the 12z short range models continue to show a band of 100-300
j/kg of SBCAPE along and ahead of the cold front, prompting the
ongoing mention of slight thunder chances. Given the strong shear
and forcing, this could result in a non-zero qlcs threat.
It's still looking like only a few hours of northwest flow shower activity
may linger late Saturday night, with the higher peaks seeing a few
flakes of snow before the moisture dissipates around daybreak
Sunday. Progressive drying and a lingering moderate pressure
gradient will be featured for Sunday, leading to a brisk, cool and
Long term /Sunday night through Thursday/...
as of 1230 PM thursday: a weak llvl ridge axis is progged to
traverse atop the southeast Continental U.S. On Monday, keeping our weather quiet with
temperatures close to the seasonal normal. Some limited return flow
moisture is slated to encroach on Tuesday but at this point it our
shower chances look debatable, certainly not more than a token small
or slight chance and probably just for the mountains. Otherwise
under a mix of sun and clouds, maximum temperatures will get a
category bump from persistance.
There is still some disagreement on the details on this next storm
system, but the 00z ec and GFS agree on a cold front and associated
band of precip crossing the forecast area late Tuesday thru early
Wednesday. Temps moderate back to slightly above normal, and precip
is expected to be all rain.
Aviation /03z Friday through Tuesday/...
for kclt and elsewhere: VFR conditions will continue at the
terminals as mid and high clouds slowly increase, thicken, and lower
through the period. Winds will become light overnight before
increasing again after sunrise. Southwest winds over the foothills
could become briefly gusty again during peak mixing Friday. Rain
shower chances will increase mainly across the western NC taf sites
toward the end of the period, particularly at kavl after 21z, but
with more solid chances just beyond the current taf period.
Outlook: increasing precipitation chances and flight restrictions
are expected with a low pressure system and associated cold front
Friday night through Saturday. VFR conditions will return Sunday
through early next week.
03-09z 09-15z 15-21z 21-00z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% high 100% high 94%
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: