Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 081942

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
242 PM EST Fri Dec 8 2017

A moist frontal zone and embedded wave of low pressure will linger
just to our southeast through tonight. Snow will continue in
most areas northwest of I-85 during this time. This system will
depart on Saturday, but moist northwest winds will bring another
shot of snow to the North Carolina mountains Saturday night. Cool
temperatures and dry weather will return Sunday and persist through
early next week.


As of 215 PM EST Friday: Snow is continuing to expand across the
area as low levels cool allowing snow to mix with the rain and
slowly change over to snow across the piedmont. Snow continues
across the mountains and foothills. Guidance in good agreement that
precip will continue through the night with just occasional breaks
as lighter precip areas move through. Given the current and forecast
trends, it appears that warning level snowfall will continue across
all the mountains and spread into the NC Foothills and NW Piedmont
where the combination of QPF and timing of snowfall creates the
highest accums. With snow already changing over across the northern
Upstate and NE GA and moving south across the NC Piedmont, advisory
level snow amounts area likely even though it will take a few hours
for temps to fall enough for snow to start sticking. Expect a very
tight gradient of temp/wet bulbs making a tight gradient of
significant accums. Right now, it looks like the southern tier of
the CWFA from Elbert to Chester will only see very light accums,
generally below an inch. Expect storm totals generally to be 6 to 9
with isolated 12 inch values across the mountains and NC foothills
near the Blue Ridge. 4 to 6 inches values for the NW piedmont. Snow
will range from 1 to 3 inches across the Southern NC piedmont and
the advisory areas of the Upstate and NE GA. The highest amounts
will generally be along and north of the I-85 corridor.

Short wave and jet streak rounding the upper trough will keep precip
going Saturday morning even as it begins to taper off from west to
east. Precip should remain snow across the mountains but could
change back to rain before ending across the piedmont as warming
occurs. Expect precip to quickly taper off by early afternoon. Snow
showers will return to the TN border counties as moisture moves back
into the area on NW flow. Any additional accums from this snow would
hold off until evening. Highs will be in the 30s across the
mountains and generally from near 40 to 45 elsewhere.


As of 200 PM Fri: Upper trough axis will swing east of the CWFA
Saturday night. In its wake, high pressure centered over the Deep
South will bring strong northwesterly low-level winds atop our
area. Given the exceptionally cold temperatures and moisture banked
up against the southern Appalachians, a rather impressive setup for
upslope snowfall will exist at least briefly overnight along the
Tenn border. Temperatures within the saturated layer will be ideal
for snow crystal growth, suggesting large snow ratios. A blend of
high-resolution QPF guidance, coupled with the NAM SLRs in the 15:1
to 20:1 range, results in an additional 0.5 to 2 inches overall. Min
temps will be in the teens in the mountains and lower to mid 20s
Piedmont. Winds in the higher elevations of the mountains still
look sufficient to bring wind chills below zero for a time early
Sunday. Gusts on the highest ridges will occasionally meet advisory
criteria, and if this area expands to lower elevations we may
issue a wind advisory, which will wrap in the wind chill concerns.

Skies will be mostly clear Sunday, downsloping winds and the
sunshine would suggest rebounding temps, but thickness values
will remain very low, and furthermore snow likely still will be
on the ground in much of the CWFA. Maxes are expected to be 10-13
degrees below normal as a result. Quiet/dry weather should continue
Monday, with sunshine and airmass modification bringing temps back
to within a couple degrees of normal.


As of 200 PM EST Friday: A broad eastern trough will remain over the
area Tuesday, with strong height falls occurring once again west of
the Appalachians. The base of the sharpening trough will cross the
region Tuesday night and then move off the eastern seaboard on
Wednesday. Most of the deeper moisture will pass north of the region
late Tuesday/Tuesday night, however, abundant low-level moisture
should wring out accumulating scattered snow showers in the western
mountain upslope areas during this period - with mainly dry
conditions east of the mountains.

A series of additional clipper-type shortwaves will cross the region
Thursday and Friday as they round the continued eastern trough, but
with much uncertainty on the timing presently. Any deeper moisture
should be brief and transitory, with the mountains exhibiting the
highest PoP in moist, westerly upslope flow. Temperatures will dip
well below climo once again as the waves reinforces the eastern
trough Wednesday through Thursday.


At KCLT and elsewhere: Conditions continue to deteriorate across the
area this afternoon with widespread IFR in rain mixing with snow
across the south and all snow at KAVL and KHKY. Expect all locations
to be IFR or LIFR this evening, with VLIFR possible as precip
intensifies. Expect snow to be the main precip at KAVL and KHKY
while rain changes to snow elsewhere except KAND where it should
remain mainly a mix. Conditions remain low after daybreak with some
slow improvement possible by early afternoon or late afternoon at
KCLT. Precip ends during the morning and could change back to rain
before ending outside of the mountains. NE winds with some gusts
possible through the evening slowly diminish overnight. Winds pick
up from the WSW for the afternoon. Winds at KAVL remain NNW through
the period.

Outlook: Any lingering restrictions will decrease Saturday evening,
with dry conditions expected at all sites into early next week. The
possible exceptions would be KAVL/KHKY with potential for northwest
flow snow Saturday night.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  81%     High  82%     Med   68%     Low   56%
KGSP       Med   70%     Med   75%     High  83%     Med   64%
KAVL       High  94%     High  85%     Med   70%     High  87%
KHKY       High 100%     High  83%     Med   66%     High 100%
KGMU       Med   76%     High  86%     High  85%     Med   63%
KAND       Med   76%     Med   65%     High  90%     Med   61%

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:


GA...Winter Storm Warning until noon EST Saturday for GAZ010-017-
     Winter Weather Advisory until noon EST Saturday for GAZ026-028.
NC...Winter Storm Warning until noon EST Saturday for NCZ033-
     Winter Weather Advisory until noon EST Saturday for NCZ068>072-
SC...Winter Storm Warning until noon EST Saturday for SCZ001>003.
     Winter Weather Advisory until noon EST Saturday for SCZ004>010.


SHORT TERM...Wimberley
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