Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
150 am EDT Friday Oct 31 2014
moisture will increase on Friday out ahead of an approaching cold
front. This front...and a strong middle level area of low pressure is
forecast to track across the region Friday night into Saturday. A
strong surface low pressure system will develop offshore on
Saturday...then track quickly north by Saturday night. Circulation
around the coastal low will bring a Canadian air mass to the region
Near term /through today/...
as of 130 am...forecast remains on track with only some high cloudiness.
Temperature/relative humidity trends look good. Min temperatures also on track. No changes for
the rest of the overnight period. Then things start to get
Remainder of previous discussion...
As of 1025 PM...going forecast still on track with mainly light winds
and mostly clear skies. Have slowed the increase in clouds...but
still have partly cloudy skies across the mountains by morning given the
clouds upstream heading this way. Otherwise...updates mainly for
An upper trough will amplify over the eastern USA through
Friday...while a ridge upstream progresses from the Rocky Mountains
to the plains. A shortwave rounding the base of this trough will
cross the southern Appalachians by daybreak...while an upper low
closes off over the Great Lakes. This deepening low will move into
the Ohio River valley by late Friday.
A nearly stationary front will remain near the Carolina and Georgia
coasts tonight...then begins moving slowly east on Friday as a
surface wave moves NE up the boundary. Meanwhile...a surface low
will fill as it moves from the Southern Plains to the Tennessee Valley.
Moisture ahead of this low will reach the southern Appalachians by
daybreak...but precipitation associated with the system will likely
not arrive until midday...when a cold front reaches the mountains
from the northwest. The front moves across our area during the afternoon...
accompanied by modest precipitation with limited lift along the
boundary. Very limited instability will be present in the
Piedmont...and convection cannot be totally ruled out...but
thunderstorms will not be mentioned at this time.
The better precipitation will follow the front in the mountains...
where robust most upslope flow will setup from the northwest. With
sufficient cold advection behind the front...precipitation will
change over to a mix of rain and snow at higher elevations during
afternoon...and all snow on the very highest peaks toward evening...
but duration appears too short for accumulations before dusk.
Minimum temperatures will run a few degrees below normal tonight in
a cool northwest flow behind the coastal front. High temperatures on Friday
will run around five degrees below normal due to cloud cover and
Short term /tonight through Sunday/...
As of 230 PM Thursday...12z guidance package remains consistent in
moving an anomalous upper low rapidly southeast from the Great Lakes into
the Carolinas on Sat. This low is in the neighborhood of 5 sd's
below normal. So we do not see this type of system very often.
Thus...we will be onguard in regard to the unexpected. With the very
good run to run model consistency...we are confident enough to go
ahead a upgrade the Winter Storm Watch in the NC mountains to a
warning for Friday night and Sat...except for Buncombe...northern
Jackson and Graham counties where a Winter Weather Advisory will be
The very potent compact vortmax/closed 500 mb low will induce
cyclogenesis east of the Outer Banks during the day on Sat... with a
deformation zone setting up from central Virginia/NC extending as far west
as the I-77 corridor on Sat. An associated cold front moving across
the area Friday night will bring a surge of very cold air with 850
mb temperatures plummeting to -6 to -8c along the Tennessee line and generally 0
to -4c across the Piedmont. The cold temperatures aloft along along with the
rapidly cooling boundary layer will allow rain to change to snow by
midnight Friday night in the moutnains...with a rain/snow mix
spreading eastward across the foothills into the I-85 corridor
toward sunrise on Sat. In the mountains...upslope flow will continue to
produce snow showers into Sat evening. Storm total snow amounts in
the Tennessee border counties will be on the order of 4-8 inches with
possibly as much as 10 inches in the higher peaks of the smokies.
Other mountains locations will see anywhere from a dusting to up to
On Saturday the bombing low along the coast will generate strong
low level winds on the order of 40-50 kts out of the northwest. Our wind gust
algorithm hits the upstate and NE Georgia with the highest gusts on the
order of 35 to 45 miles per hour...which would be below high wind watch
criteria. Precipitation ends for the most part by Sat evening...except for
some lingering snow showers in the NC moutnains adjacent to Tennessee.
Clearing conditions will occur Sat night but atmosphere may stay
mixed enough to prevent widespread freezing temperatures outside the
mountains...so no freeze watch for now. Temperatures stay well below climatology
for sun even with full sunshine.
Long term /Sunday night through Thursday/...
as of 100 PM Thursday...medium range models are in decent agreement
in building deep layered ridging atop the southeast Continental U.S. On Monday and
translating ridge center offshore on Tuesday. It now looks like maximum
temperatures will creep back to within 5 degree f of climatology by Tuesday.
It remains to be seen just how much if any deeper convection develops
within the warm sector on Wednesday with the best model response
still west of the mountains by the evening hours. For now...will maintain
token small or slight shower chances and continue to moderate
Aviation /06z Friday through Tuesday/...
at kclt...expect VFR conditions to continue through the
period...although the situation will be going downhill at the end of
the forecast period. Until then...mainly high clouds through the early
to middle morning with a light NE wind...followed by thickening mostly
altocu ceilings. By middle/late afternoon...the wind should be light
and variable and may change between northwest and SW often. At that time...
a low cloud ceiling should move in from the northwest ahead of the
approaching low...but still VFR. The latest model guidance is in
good agreement with developing light precipitation into the clt metropolitan area
around sunset. A consensus of the guidance suggests a prevailing
light rain...but with still a VFR category visibility...after 02z.
Wind at that time should settle into a north component. No issues with
precipitation type until after 06z Saturday.
Elsewhere...VFR through the daylight hours Friday. Light and
variable winds and increasing middle/high clouds expected through middle
morning. Low VFR and middle clouds increase through the day Friday with low
VFR ceilings expected by afternoon at kavl. Winds turn west-southwest Friday afternoon
ahead of the approaching cold front. However...winds remain northerly at
kavl. Kavl also has the best chance of seeing any rain showers by late in the
afternoon...which was included as a vcsh at this time. The steadier
rain should move into the mountains by sunset. Have included the rain
prevailing after 02z at kavl...at which time the ceiling should drop
to MVFR. Preliminary indication is that precipitation could change over to
snow showers at kavl as early as 05z. A similar progression is
noted at khky...but precipitation was kept liquid. Other taf sites only
have a vcsh after 02z or 03z...owing to low confidence.
Outlook...light precipitation will develop across the entire area late
Friday night. Some restrictions are possible...especially in the
mountains where even some snow showers are expected late Friday
night and Saturday. VFR beyond Sunday.
NC...Winter Storm Warning from 8 PM this evening to 8 PM EDT
Saturday for ncz033-048>052.
Winter Weather Advisory from 8 PM this evening to 8 PM EDT
Saturday for ncz053-058-059.