Winter Storm in North Carolina, December 8 to 9, 2018

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
957 PM EST Sat Dec 8 2018

.SYNOPSIS...
With cold Canadian high pressure to our north and low pressure
passing to our south, we are having a major winter storm.  The
low pressure moves off the Carolina coast Sunday evening taking
most of the wintry weather with it.  The last of the light
precipitation finally ends Monday night when the upper trough
passes. Cool high pressure will be in control Tuesday and Wednesday,
then the next storm system arrives at the end of the week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 930 PM EST: No significant changes to the forecast as of mid-
evening. Caught a nice radar bright band strung out west to east
across the nrn Upstate earlier this evening, which essentially
marked the transition zone between the rain with some sleet
across the srn 2/3 of metro GSP, and the mostly snow across nrn
Greenville and nrn Spartanburg counties. That boundary has since
drifted north toward the NC state line. Meanwhile...the northern
extent of the light precip can't seem to make it into the nrn
foothills and nw Piedmont, which is only allowing temps up in that
region to cool off this evening, which means lower wet bulb temps,
which means even more certainty that precip will either start as
snow or quickly change to snow in the I-40 corridor east of the
mtns later tonite. We await more guidance before applying any
mid-course corrections.

Otherwise, a 1013 mb surface low center was analyzed over southeast
Louisiana this afternoon, while water vapor imagery and RAP upper-
level initializations reveal a vigorous southern stream wave over
east Texas. There is good model agreement on the eastward evolution
of these features, but subtle, yet important differences exist with
regard to the thermal profiles. The 500 mb low over east TX will
lift northeast over the MS River Valley tonight and then across
the Appalachians on Sunday. Meanwhile, the surface low center
is expected to move across southern GA tonight and then exit the
southeast coast by midday Sunday. Mid-level frontogenetical forcing
over the baroclinic zone draped over our region this afternoon will
give way to robust deep forcing overnight. These mechanisms will
come together atop the western Carolinas and northeast Georgia in
the form of strong, deep-layer Q-vector convergence ahead of the
main wave, strong right entrance region upper jetlet divergence,
and improving isentropic lift and upslope in the stout southeasterly
or easterly 850 mb flow. The best forcing and deepest moisture
will arrive just as 850 mb temperatures cool rapidly from north to
south circa 06Z-12Z. A blend of cooler GFS and warmer NAM profiles
were used for this period. The 850 mb low center track through the
SC midlands/piedmont will be very favorable for heavy snow across
the southern Appalachians and adjacent NC foothills. In addition,
the very classic and deep cold air damming east of the Appalachians
will drive freezing or near freezing surface temperatures nearly
through the southern piedmont to permit freezing rain and icing
to mix in at times.

All told, the warnings, advisories, and amounts still look
reasonable with predominantly snow across most of the mountains and
foothills, a broader sleet band developing early Sunday morning,
with freezing rain making the best southern tier appearance by
daybreak Sunday. As the 850 mb low pivots off to the southeast
early Sunday, thicknesses will cool once again to lead to more
dominant snow/sleet returning from the north. This transition is
complicated by some mid and upper level drying wrapping in from
the southwest Sunday afternoon. There is some potential for more
freezing drizzle and light freezing rain in these dry pockets
where ice nuclei are unavailable, but the moisture in the profiles
is quite uncertain and continued forcing west of the surface low
could lead to some ice nucleation. Will thus stick to the top-down
hydrometeor ptype approach through the duration of the event with
the assumption that ice nuclei exist. At any rate, precipitation
rates will experience a lull Sunday afternoon and early evening
as the better forcing moves east for most areas.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 215 PM Saturday: The weakening phase of CAD will begin
Sunday night, with both the low pressure and the parent high
having drifted east off the Atlantic coast. The low to midlevel
flow over the wedge airmass will have backed somewhat, but still
driving reasonably strong WAA into the western Carolinas. The
depicted 500mb pattern is complex, with an ill-defined shortwave
and vort max slowly moving over our CWFA from the west. As the
CAD-associated forcing diminishes, the shortwave will make up for
it to some degree. Accordingly, 850mb heights recover little in
the wake of the sfc low. The warm advection is expected to maintain
sufficiently warm temps in the midlevels that a change from rain to
a wintry mix will occur over a portion of the Piedmont overnight,
with precip rates likely to pick up again early Monday. Moisture
becomes increasingly shallow as a new area of continental high
pressure exerts increasing influence, but our remaining PoPs will
be bolstered by upper divergence and/or deformation occurring
with another cutoff shortwave diving into the Deep South on
Monday. As this feature moves south of the area Monday night and
subsidence/drying continue, we finally are able to let PoPs drop
below slight-chance.

Sfc temps in this period are perhaps the least confident part
of the fcst. The expectation that heavy snow/ice cover will be
present over most of the area implies we should continue to favor
the colder guidance into Monday. The higher resolution members, such
as the NAMNest and HiRes windows, seem to show the wedge weakening
enough to allow some warming over the Piedmont, and becoming shallow
enough for temps to warm appreciably Sunday night in the higher
elevations along the Blue Ridge, plus a portion of the Savannah
River Valley. For now these sources have been minimized in the fcst,
but guidance still supports enough warming for wintry precip to
change to rain over some areas. Additional accumulation after 00z
Mon is not expected to be significant compared to what falls prior
to that time. Monday's highs will be high enough to support some
partial melting, though with generally mostly cloudy or overcast
skies it likely won't reduce snow/ice pack very much. Roadways
are likely to become wet and with much colder temps still expected
Monday night, black ice will be widespread around the region. After
the end of the Winter Storm Warning we likely will need to issue
an Advisory to cover the black ice threat through early Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 235 PM EST Saturday: The guidance agrees an a very energetic
storm system affecting the area next weekend. However, there are
some significant differences in the details. Before then, expect dry
and cold high pressure for Wednesday. Lows will be 10 to 15 degrees
below normal with highs 5 to 10 degrees below normal.

The high will remain ridged in place across the area Thursday in a
cold air damming pattern. The center of the high is progressive so
this will not be classical damming. Moisture begins to increase
ahead of the next weather system with weak isentropic upglide as
well. Small rain chances will develop during the day. Lows will
range from near normal to 5 degrees below normal with highs around
10 degrees below normal. If the precip starts early enough, then
some would fall as snow before warming begins. However, the chance
of any accums is near zero.

As mentioned above, the guidance agrees that a strong upper low
forms in a deep trough over the central CONUS on Friday. The GFS and
Canadian are farther north and faster than the ECMWF. The GFS has
the upper low moving into the TN valley Friday and to the mid-
Atlantic on Saturday. The ECMWF has the low moving to near Mobile
Friday and to central GA on Saturday. The GFS swings an occluding
front across the area Friday with the occluded low moving east
across VA Saturday. The ECMWF has the occluding low passing by to
our south in Miller-A fashion. Both models have good in-situ damming
forming but are still relatively warm keeping the precip liquid
Friday. The GFS is very dynamic with strong shear and helicity
developing. There is some elevated instability ahead of the front
across the I-77 corridor. The ECWMF has little to no instability.
The GFS shows a long period of NW flow snow developing with some
snow showers breaking containment across the NC foothills and
piedmont. The ECMWF would suggest snow showers across much of the
area with the farther south low. Given the big change in the ECMWF
forecast, have trended toward the GFS solution with low confidence.
That said, it does look like Friday will be wet either way, so have
likely PoP for that period. Kept thunder out for now. Have highs
warming above normal for Friday and cooling to near normal for
Saturday. Lows will be above normal both mornings.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
At KCLT and Elsewhere: Damming continues to build in with precip
overspreading the area. PL reported at KCLT at 23z, it's been
snowing for a while at KAVL, and precip hasn't gotten to KHKY just
yet; still all rain in the Upstate but the cooling temps are slowly
working south. Expect a mess of wintry precip across the area, with
KGMU/KGSP/KCLT seeing the most mix, while KAVL/KHKY should see
mostly -SN. KAND mostly -RA with some -FZRA or PL mixing in in the
morning. Cigs will vary between LIFR and low MVFR through the
period, with vsbys sometimes <1/2SM in the heavier SN. Should see
some increasing gusts across the Piedmont TAFs tomorrow morning as
well, and have introduced LLWS at KAVL per latest guidance. Precip
rates will diminish Sunday afternoon but incredibly messy until then.

Outlook: The winter storm will linger late Sunday through Monday,
with plenty of wintry ptypes and low restrictions. Snow showers may
get reinforced from the west Monday as an upper disturbance arrives
from the west. Significant improvement is not expected until Tuesday.

Confidence Table...

            03-09Z        09-15Z        15-21Z        21-00Z
KCLT       Med   72%     Med   64%     Med   78%     High 100%
KGSP       Med   75%     Low   58%     High  91%     High  91%
KAVL       Low   56%     Med   75%     High  86%     High 100%
KHKY       Med   78%     Med   69%     Low   58%     High 100%
KGMU       Med   77%     Low   58%     High  91%     High 100%
KAND       Med   78%     Med   75%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Winter Storm Warning until noon EST Monday for GAZ010-017.
     Winter Storm Warning from 1 AM Sunday to noon EST Monday for
     GAZ018.
     Winter Weather Advisory from 1 AM Sunday to noon EST Monday
     for GAZ026-028-029.
NC...Winter Storm Warning until noon EST Monday for NCZ033-035>037-
     048>053-056>059-062>065-068>072-082-501>510.
SC...Winter Storm Warning until noon EST Monday for SCZ001>003-
     005>009.
     Winter Storm Warning from 1 AM Sunday to noon EST Monday for
     SCZ004-010-012>014.
     Winter Weather Advisory from 1 AM Sunday to noon EST Monday
     for SCZ011-019.

&&

SYNOPSIS...DEO
NEAR TERM...HG/PM/TDP
SHORT TERM...Wimberley
LONG TERM...RWH
AVIATION...TDP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
1105 AM EST Sat Dec 8 2018

NCZ033-035>037-049-050-056-057-068>072-082-501>506-508-510-
SCZ005>009-091615-
Avery-Alexander-Iredell-Davie-Yancey-Mitchell-Catawba-Rowan-
Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Greater Rutherford-Eastern Polk-
Greater Pickens-Greater Greenville-Spartanburg-Cherokee-York-
1105 AM EST Sat Dec 8 2018

...WINTER STORM WARNING IN EFFECT FROM 7 PM THIS EVENING TO NOON EST
MONDAY...

This Hazardous Weather Outlook is for piedmont North Carolina,
western North Carolina and upstate South Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Winter Storm Warning.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Winter Storm Warning.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to report snow and ice accumulations to our
office.

GAZ010-017-NCZ048-051>053-058-059-062>065-507-509-SCZ001>003-091615-
Rabun-Habersham-Madison-Swain-Haywood-Buncombe-Graham-
Northern Jackson-Macon-Southern Jackson-Transylvania-Henderson-
Rutherford Mountains-Polk Mountains-Oconee Mountains-
Pickens Mountains-Greenville Mountains-
1105 AM EST Sat Dec 8 2018

...WINTER STORM WARNING IN EFFECT UNTIL NOON EST MONDAY...

This Hazardous Weather Outlook is for northeast Georgia, western
North Carolina and upstate South Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Winter Storm Warning.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Winter Storm Warning.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to report snow and ice accumulations to our
office.

GAZ018-SCZ004-010-012>014-091615-
Stephens-Greater Oconee-Anderson-Laurens-Union-Chester-
1105 AM EST Sat Dec 8 2018

...WINTER STORM WARNING IN EFFECT FROM 1 AM SUNDAY TO NOON EST
MONDAY...

This Hazardous Weather Outlook is for northeast Georgia and upstate
South Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Winter Storm Warning.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Winter Storm Warning.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to report snow and ice accumulations to our
office.

GAZ026-028-029-SCZ011-019-091615-
Franklin-Hart-Elbert-Abbeville-Greenwood-
1105 AM EST Sat Dec 8 2018

...WINTER WEATHER ADVISORY IN EFFECT FROM 1 AM SUNDAY TO NOON EST
MONDAY...

This Hazardous Weather Outlook is for northeast Georgia and upstate
South Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Winter Weather Advisory.

In addition to the wintry weather, periods of heavy rain are possible
tonight. Isolated flooding may develop, especially in areas where
there is more rain than wintry mix.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Winter Weather Advisory.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to report snow and ice accumulations to our
office.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
836 PM EST SAT DEC 08 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0835 PM     SNOW             1 N SALUDA              35.24N  82.35W
12/08/2018  M4.7 INCH        POLK               NC   COCORAHS

            ALL SECONDARY ROADS COVERED WITH SNOW.

&&

TDP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
914 PM EST SAT DEC 08 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0835 PM     SNOW             3 S OLD FORT            35.59N  82.18W
12/08/2018  M1.0 INCH        MCDOWELL           NC   BROADCAST MEDIA

            CROOKED CREEK COMMUNITY

&&

TDP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
939 PM EST SAT DEC 08 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0939 PM     SNOW             HENDERSONVILLE          35.32N  82.46W
12/08/2018  E5.0 INCH        HENDERSON          NC   SOCIAL MEDIA

&&

TDP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
943 PM EST SAT DEC 08 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0942 PM     SNOW             ETOWAH                  35.32N  82.60W
12/08/2018  M2.8 INCH        HENDERSON          NC   SOCIAL MEDIA

&&

TDP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
945 PM EST SAT DEC 08 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0945 PM     SNOW             FAIRVIEW                35.52N  82.40W
12/08/2018  E2.0 INCH        BUNCOMBE           NC   SOCIAL MEDIA

&&

TDP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
955 PM EST SAT DEC 08 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0955 PM     SNOW             2 E TIGERVILLE          35.07N  82.34W
12/08/2018  E1.5 INCH        GREENVILLE         SC   SOCIAL MEDIA

            SNOW AND SLEET MIX.

&&

TDP