Winter Storm in North Carolina, January 30 to 31, 2021

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
342 PM EST Sat Jan 30 2021

.SYNOPSIS...
A moist cold front and associated precipitation arrives from the
west tonight into Sunday, with some wintry precipitation possible
once again mainly across the mountains and along and north of
Interstate 40. Cool high pressure builds in by Tuesday and continues
through Wednesday before another cold front approaches from the west
by the end of the week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 220 PM EST: Patchy light precip associated with an upper jet
and mid level short wave will cross the area late this afternoon and
early evening. Where temps are cold enough, snow and/or sleet will
mix with the rain. No significant accumulations are expected with
this round of precip. Expect a brief break before the heavier precip
moves in overnight.

Guidance still on track for a Miller B low pressure system to move
into the area tonight and to our east Sunday. Forcing and deep
moisture ramp up quickly near midnight with precip spreading across
the area before daybreak. Forecast soundings and partial thickness
values still suggest a typical, messy Miller B p-type forecast for
this system. Temps aloft wet bulb down below freezing before a warm
nose kicks in and strengthens late tonight into Sunday. An in situ
wedge forms as precip falls, bringing temps down to near or below
freezing across the Warning and Advisory area. Since it is an in
situ wedge, the cold temps will not be locked in and will warm
around the edges through the morning with all areas above freezing
by afternoon. Precip still expected to start as snow and sleet in
the colder air then slowly change to freezing rain and rain as the
warm nose strengthens and cold pool erodes. Only change to Warning
and Advisories was to add Madison County to the above 3500 feet
Advisory as their higher elevations will see some accumulation of
sleet and freezing rain. Snow amounts will range from 2 inches in
the southern portion of the Warning to 6 inches along the northern
Blue Ridge. Ice amounts will be as high as 0.2 inches. Snow amounts
of 1 to 2 inches with ice amounts up to 0.2 inches expected in the
Advisory.

Will keep the SPS in place for locations along and north of I-85 not
in the Warning or Advisory as these locations may see a light mix of
mainly rain/freezing rain toward daybreak. Could see a light glaze
on elevated surfaces there, but no significant accumulations.

The timing of the Warning and Advisory still looks good as precip
should become all rain by early afternoon. Sunday's highs will show
a typical Cold Air Damming pattern with 30s to low 40s common
outside of the mountains and along the Blue Ridge escarpment. Highs
will rise to the lower 50s going westward to the lower valleys near
the TN border.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 230 pm Saturday: As we begin the short-term period Sunday
evening, rainfall chances will be rapidly diminishing from west
to east across the Piedmont behind the near-term storm while flow
gradually turns northwesterly behind the cold front.  Over the
western mountains, however, upslope flow snow showers will already
be occurring in earnest Sunday evening with a northwest flow snow
pattern well underway, especially across the highest elevations.
As CAA/nocturnal cooling strengthens overnight, snow levels will
continue to fall and snow showers will become more widespread,
especially as we approach daybreak Monday, with low temperatures
near or below freezing for most of the southern Appalachians.
Temperatures will fail to recover much on Monday across the area
due to continued cold advection.  Temperatures will likely peak
10-13 degrees below normal over the mountains and 7-10 degrees
below normal to the east. Many mountain elevations will not get
out of the lower 30s. As the upper low slowly pivots east of
the area during the day, deep- layer NW flow forcing and
moisture should enhance snow shower coverage and intensity,
especially along and near the TN border. Vorticity advection,
combined with favorable, steep lapse rates associated with the
upper low, will result in light rain showers breaking out over
the Piedmont Monday afternoon, especially across the eastern
zones away from downsloping effects, and some isolated pockets
of light graupel mixing in cannot be ruled out. Given the ideal
NW flow fetch, the strongest part of the event will occur Monday
into Monday evening, but snow showers are expected to become
more confined to the TN border counties overnight Monday into
Tuesday morning as the flow gradually veers NNW and N behind the
upper low. We expect the snow showers to finally end Tuesday
afternoon.

Given the pattern, notable accumulations are expected across the
mountains, primarily across the TN border counties through early
Tuesday afternoon. Moisture will be rather abundant and deep
for the continental airmass in place with sounding profiles
showing impressively persistent saturation around the -10C
dendritic growth zone layer from Monday morning through early
Tuesday morning.  This combined with the duration of the event and
deep-layer orientation of the flow through Monday evening supports
accumulations that may exceed Warning criteria (>4" in 24 hours)
across the higher elevations and along the TN border.  However,
in coordination with our neighbors we will not be introducing
a Watch for this package given we still have one winter storm
to get through first. Furthermore, there continues to be some
uncertainty about the duration of the best upslope flow (though
models have become more bullish in that regard) and the strength of
the low-level lapse rates required for higher accums.  Therefore,
the confidence in Warning criteria is not yet high enough to
justify a hazard product at this time.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 230 pm Saturday: The extended is highlighted by a gradual
warming trend, as the deep upper trough over the eastern CONUS is
replaced by a developing longwave ridge.  Associated height rises
will dramatically increase thicknesses over the Southeast Wednesday
into Thursday as seasonable, dry surface high pressure dominates the
sensible weather.  Temperatures will slowly rebound with highs near
normal for Wednesday and 2-5 degrees above normal for Thursday.
The surface high pressure will slide offshore Thursday, and the
clockwise flow will put our area in a developing southerly flow
(WAA) regime.  The upper-level ridge axis will pass by late
Thursday into Friday as northern- and southern-stream systems
propagate across the central CONUS.  Reinforcing shortwave energy
will amplify the southern stream system over the Plains Friday
into Saturday as an attendant cold front approaches our region.
The favorable southerly flow should yield high temperatures into
the lower 60s east of the mountains, or 5-9 degrees above normal,
for Friday.  Only the highest elevations will bottom out below
freezing Friday morning.The additional cloud cover and increasing
precip for Saturday will suppress high temperatures a bit but with
highs still near 60 across the Piedmont they will remain above
normal. Not surprisingly this far out, there are FroPa timing
differences between the 12Z ECMWF and 12Z GFS/Canadian
solutions but either way we are expecting rainfall chances to
increase Friday evening into Saturday as the cold front moves
into the mountains. The 12Z GFS and Canadian solutions are
messier as a secondary wave develops along the front, resulting
in anafront precip Saturday afternoon whereas the ECMWF is
cleaner and more progressive. Rainfall totals appear manageable
at this time.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: VFR continues through the afternoon,
although with lowering cigs and some patchy light rain or even a
wintry mix moving in from the west. Any precip will be short lived
and timing still questionable, so kept out of the TAFs for now.
Worsening conditions and better rain chances move in overnight.
Expect cigs to fall through MVFR to IFR by daybreak. MVFR to IFR
vsby expected as well. Precip will be mainly rain over SC and KCLT.
Can't rule out a brief mix with sleet or even -FZRA if temps fall
far enough. Better chances of prolonged wintry precip at KAVL and
KHKY. KAVL may see snow and/or sleet to start, but should quickly
transition to sleet/freezing rain, with freezing rain continuing to
near noon. KHKY will see similar conditions, but sleet will last
longer before transitioning. Southerly winds this afternoon turn ENE
then NE overnight into Sunday. KAVL will see S to SE wind throughout
with low end gusts overnight.

Outlook: Expect only rain for the bulk of the afternoon Sunday with
precip and vsby restrictions tapering off outside of the mountains.
Low cigs will continue through the day. A period of NW flow snow is
likely over the mountains on Monday into Monday night before the
rest of the area dries out. Low cigs may continue outside of the
mountains before drying develops.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High  98%     High  92%     High  96%
KGSP       High 100%     High 100%     High  89%     High  86%
KAVL       High  97%     High 100%     High  89%     High  92%
KHKY       High 100%     High  82%     High  91%     High  92%
KGMU       High 100%     High  98%     Med   79%     High  89%
KAND       High 100%     High 100%     High  80%     High  91%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables are available at
the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Winter Weather Advisory above 3500 feet from 8 PM this evening
     to noon EST Sunday for NCZ048-051-052-059-063.
     Winter Weather Advisory from 8 PM this evening to noon EST
     Sunday for NCZ036-037-053-056-057-064-068-069-508-510.
     Winter Storm Warning from 8 PM this evening to 4 PM EST Sunday
     for NCZ033-035-049-050-065-501>507-509.
SC...None.

&&

SYNOPSIS...DEO
NEAR TERM...RWH
SHORT TERM...JMP
LONG TERM...JMP
AVIATION...RWH

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
644 AM EST Sat Jan 30 2021

NCZ033-035-049-050-065-501>507-509-311145-
Avery-Alexander-Yancey-Mitchell-Henderson-Caldwell Mountains-
Greater Caldwell-Burke Mountains-Greater Burke-McDowell Mountains-
Eastern McDowell-Rutherford Mountains-Polk Mountains-
644 AM EST Sat Jan 30 2021

...WINTER STORM WARNING IN EFFECT FROM 8 PM THIS EVENING TO 4 PM EST
SUNDAY...

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

None.

NCZ036-037-051>053-056-057-059-063-064-068-069-508-510-311145-
Iredell-Davie-Swain-Haywood-Buncombe-Catawba-Rowan-Northern Jackson-
Southern Jackson-Transylvania-Cleveland-Lincoln-Greater Rutherford-
Eastern Polk-
644 AM EST Sat Jan 30 2021

...WINTER WEATHER ADVISORY IN EFFECT FROM 8 PM THIS EVENING TO NOON
EST SUNDAY ABOVE 3500 FEET...

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

.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...

None.

GAZ010-NCZ048-058-062-070>072-SCZ001>003-006>008-311145-
Rabun-Madison-Graham-Macon-Gaston-Mecklenburg-Cabarrus-
Oconee Mountains-Pickens Mountains-Greenville Mountains-
Greater Greenville-Spartanburg-Cherokee-
644 AM EST Sat Jan 30 2021

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

.DAY ONE...Today and tonight.

For the areas surrounding the Winter Storm Warning and Winter Weather
Advisories, brief periods of wintry weather, mainly sleet or
freezing rain. Isolated very light accumulations will be possible on
elevated surfaces such a bridges or overpasses.

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

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

GAZ017-018-026-028-029-NCZ082-SCZ004-005-009>014-019-311145-
Habersham-Stephens-Franklin-Hart-Elbert-Union NC-Greater Oconee-
Greater Pickens-York-Anderson-Abbeville-Laurens-Union SC-Chester-
Greenwood-
644 AM EST Sat Jan 30 2021

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

.DAY ONE...Today and tonight.

No hazardous weather is expected at this time.

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

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

Lane