Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1238 PM EDT Tuesday Oct 6 2015
dry Canadian high pressure will build across the region through
Thursday. Moist southwest flow will develop ahead of an approaching
cold front on Friday...with the front crossing the forecast area
early Saturday. Dry conditions will return behind the front through
early next week.
Near term /through tonight/...
as of 1230 PM...no sigfnt changes needed to the grids. Updated sky
grids to handle lingering low clouds far west associated with surface
mesolow. Otherwise...nominal adjs needed to the T/dew point grids. Maximum
temperatures were also bumped up a couple degrees in various locales.
As of 930 am...low clouds persist across the mountain valleys this
morning. Expect a gradually break up after thicker cirrus moves to the
east. Hour/ly temperatures are running a little warmer in spots within
differential heating and the forecast grids have been updated.
As of 650 am...the current forecast appears in great shape. I will
update temperatures to align with observation.
As of 315 am...latest satellite images indicated an expanding area
of cirrus clouds drifting east across the southern Appalachians.
Condensation pressure deficits will decrease sharply during the pre
dawn hours within the mountain valleys. Based on forecast soundings and
saturated soil conditions...fog and low ceilings may develop between
9z to 13z. However...the arrival of the high clouds may decrease the
potential for dense fog. Low clouds and valley fog will dissipate
rapidly after sunrise. Weak surface high pressure should linger across
the County Warning Area today...supporting light north-northeast wind. Insolation should result
in afternoon highs in the low to middle 70s.
Tonight...surface high pressure is expected to build southward across
the forecast area. Winds should remain light from the north as high clouds
thin. A blend of preferred temperature guidance indicates that low
temperatures will range in the 50s across the region...with u40s
possible across the I-40 corridor.
Short term /Wednesday through Thursday night/...
as of 300 am EDT Tuesday...deep layer northwest flow is expected on
Wednesday between central Continental U.S. Upper ridging and a broad East Coast
trough. Anticipate northerly flow at lower levels as dry surface
high pressure builds over to the north of the region. The upper flow
will become more zonal in nature on Thursday as heights fall across the
upper Midwest and a cutoff low persists near West Texas. Weak SW return
flow at low levels may allow some moisture and instability to return
the southern Appalachians by Thursday afternoon...but with little
more than isolated mountain showers expected. Temperatures will
climb well above normal through the period.
Long term /Friday through Monday/...
at 305 am EDT Tuesday...the northern stream system digging southeast
from the upper Midwest will become progressive...with the best deep
layer forcing crossing the Appalachians late Friday through Friday night.
There is very Little Gulf moisture tap expected with the frontal passage
Friday night and a band of mainly scattered showers will be
advertised. The latest GFS also features a bit more surface based
instability...with 500 to 1000 j/kg of SBCAPE across the mountains
Friday afternoon ahead of the cold front. This will permit an isolated
thunderstorm mention as well.
Brief upslope showers may linger along The Spine of the southern
Appalachians in continued moist northwest flow Sat morning.
Otherwise...anticipate downslope drying behind the front. A more
amplified northwest flow pattern will then develop Sunday through
Monday with dry surface high pressure dominating behind the
departing cold front. Cooler than climatology temperatures on Saturday and
Sunday will bounce back on Monday.
Aviation /18z Tuesday through Sunday/...
at kclt and elsewhere...no flight restrictions across all non/mountain
taf sites through the period. Deep high pressure will continue to
build across the region and make for light north/ly or vrb winds. Kavl
will see lowering ceilings overnight possibly into the IFR range and IFR
visibility as mesoscale low lingers over the mountain spine. MVFR ceilings at khky
overnight. There is a low-end gust potential this afternoon...but
not enough confidence to include in taf at this time.
Outlook...dry weather is expected through Wednesday with a few mountain
showers possible Thursday afternoon. Shower chances increase on
16-22z 22-04z 04-10z 10-12z
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 86%
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: (must be lower case)