Hail and Damaging Winds in North Carolina, March 27, 2021

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1008 AM EDT Sat Mar 27 2021

.SYNOPSIS...
A warm front is expected to move northward across the area today,
keeping our weather active through tonight. A strong cold front
should approach from the west late tonight and then move across the
western Carolinas and northeast Georgia on Sunday with another round
of thunderstorms. Behind the front, temperatures will return to
normal as high pressure builds in for Monday. More unsettled weather
looks to be in store for the region by the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
1000 AM Update...The fcst is in pretty good shape. Made some minor
adjs to cloud cover and temps. The SPS has increased the severe risk
to the Slight category for most of the FA this afternoon. This makes
senses, as the latest HRRR runs continue to show good convec
development along a warm front this afternoon. The degree of severity
and location with these storms still depends on where and how strong
an insitu wedge develops over the next few hrs. For now, the best
chance for severe storms, including possible supercells, looks to be
across the srn NC mtns and foothills, NE GA, and across the nrn
Upstate where the wedge bndry will be the most distinct.

Otherwise, an upper anticyclone continues to dominate over FL,
while a vigorous upper trough digs across the Northern Plains to
the Southwest. An amplifying flow pattern will allow a warm front to
activate across the Gulf States and lift northward today. Convection
is already firing from northern MS to SC Midlands. The CAMs
have had trouble initializing the convection, but the HRRR has
had fairly good run-to-run consistency of the evolution of the
convection thru the day today. If the HRRR is correct, we will
have some discrete, rotating storms this aftn across western NC,
with convection peaking just east of the FA later in the aftn. But
the better severe threat will definitely be to our west, where
all the ingredients are in place. The new Day 1 Outlook has an
Enhanced risk over the Mid-South, with a Marginal risk across the
entire FA (A slight risk does reach the Smokies). In any case,
there are a range of outcomes today, as some CAMs, including the
NAMnest develop a lot more convection early this morning and set up
an in-situ wedge that keeps the better sfc-based CAPE only along
the southern fringes for the rest of the day. Meanwhile, the HRRR
has a lot less morning precip, and has 1500-2000 J/kg of sbCAPE
with 50 kts of 0-6 km bulk shear in the aftn. To make things even
more uncertain, both HRWARW and HRWNMM organize convection into
an MCS over eastern TN that crosses the mountains this aftn and
pushes thru the entire FA. With all that said, I think at least
some damaging wind threat will exist with any convection that
develops. The big question is perhaps is there enough upper support
for intense updrafts. If we manage any supercells, hail and even
an isolated tornado threat cannot be ruled out, but confidence is
still low. Another concern the flooding potential. Fortunately,
storms should have good motion, and I don't see much signal of
training storms. With that said, isolated flooding will be possible,
given the high river levels. Otherwise, expect mostly cloudy skies
and with temps generally 5-10 deg above normal.

Whatever convection does develop, guidance is in good agreement that
a cold pool or in-situ wedge will set up tonight, with additional
scattered showers possible over the wedge overnight. A 50+ kt SWLY
LLJ will begin to work into the NC mountains during the pre-dawn
hours as a cold front approaches from the west. Upslope areas may
see some heavy rain, and highest peaks could see advisory-level
gusts above 45 mph. Lows will be well above normal under cloudy
skies.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
As of 315 AM EDT Saturday: By daybreak on Sunday, our attention
will shift to the next round of showers and thunderstorms expected
to be approaching from east TN. The timing of this convection
will be the key to how Sunday plays out in terms of the severity
of thunderstorms and the high temps. At least the guidance is
in good agreement that showers and storms will be numerous,
if not widespread, at some point during the daytime hours. The
culprit will be a strong cold front driven east by a mid/upper
trof making steady progress across the TN/OH valley. Forcing
should be excellent and moisture more than adequate. A linear
convective mode looks to be favored. The question will be...when
does the line of showers/thunderstorms arrive? The GFS and HRRR
have the line moving into the mtns as early as mid-morning, while
the NAM and the Hi-res WRF variants have a later timing. If later,
we have more of a chance to destabilize to a greater degree east
of the mtns through early afternoon, and thus more of a chance
for severe weather, assuming pre-frontal showers over the Piedmont
don't contaminate the air mass. One plausible scenario would be for
a fairly well organized line of storms to move across the mtns in
the morning hours and then come off the Escarpment during the early
afternoon and then move across the Piedmont of the Carolinas in
the mid/late afternoon. The Slight Risk across the entire forecast
area, shown in the Day 2 Convective Outlook, looks like a safe bet
given the linear nature of the convection, even though the CAMs
have a stronger presentation once the line moves east of the fcst
area. In this scenario, the line would pass with sporadic reports
of wind damage and perhaps some hail just about anywhere across
the fcst area. Another concern would be if we retain enough shear
in the environment to support embedded rotating updrafts. Agree
with the Day 2 that the potential looks better to our east for more
widespread wind damage/tornado threat based mainly on the timing,
but it is certainly possible this intensification could happen
over the I-85 corridor. A flood threat will also exist given the
antecedent conditions, but the linear storm nature favors a short
duration of heavy rain that will limit rainfall amounts. The high
temps Sunday are entirely dependent on the timing of the storms,
but should be above normal. The storms should exit to our east in
the early evening as the cold front passes, with some lingering
westerly flow upslope shower activity along the TN border that
will slowly diminish through late evening.

In the wake of the cold frontal/mid/upper trof axis passage, sfc
high pressure will build in from the west Sunday night as a broad
flat upper ridge moves in from the west on Monday. Sky will clear
and temps will fall back close to normal with a drier air mass.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 450 am EDT Saturday: The upper flow pattern should remain
progressive into the medium range part of the forecast. On Monday
night, the axis of a broad upper trof should move off the East
Coast, taking sfc high pressure along with it. A weak system along
the Gulf Coast will start to lift out to the N/E, but the timing
and extent of the moisture/light precip is uncertain. The forecast
follows closer to the GFS depiction of better precip chances moving
past to the east on Tuesday morning, followed by a relative lull
later in the day. By that time, the upper pattern should already
be amplifying as an upper trof digs over the Rockies. By Tuesday
night and Wednesday, as this next system moves out over the Plains,
the strengthening SW flow aloft will allow for moisture to return
from the Gulf. Important model differences creep in with how
a cold front is handled by Wednesday. The latest ECMWF has the
boundary moving a bit faster and with more moisture/precip in
the warmer air along and ahead of the front, while the GFS has
more of the precip behind the front. The problems would be with
the ECMWF because it would increase the QPF and perhaps renew our
hydro problems/concerns. Any severe storm threat would probably
be greatest that afternoon/evening ahead of the front, which
would cross the region by late evening. Precip chances were kept
in check for the time being. Precip should end from the west by
around daybreak Thursday. The deepening mid/upper trof would cross
the area early Thursday, behind which a cool Canadian high pressure
air mass would build in for the remainder of the period. This air
mass will remind us that it is still early Spring as temps are fcst
to drop back to about ten degrees below normal, possibly with some
frosty mornings late in the week. Temps should moderate over the
next weekend.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: A moist warm front will lift north into the
area today, producing scattered showers (and possibly some embedded
TS) this morning as the warm front approaches, but the greatest
coverage is still expected in the 18-24z time frame. Still unclear
on the exact timing and convective mode. Some high-res models
depict more of a linear storm mode, but others keep them more
discrete/supercell. Storms will be handled by tempo groups since
they start within 9 hours of the 12z TAFs. Scattered to numerous
showers will continue into this evening as the warm front continues
to drift north. Winds will be light and variable this morning, but
favor a SW direction by midday and thru the aftn. Then winds shift
to more of a N or NE behind the main tstms this evening. Expect
mainly VFR cigs today, but MVFR to IFR cigs develop tonight.

Outlook: A line of thunderstorms is expected to cross the area late
morning thru mid-aftn Sunday. VFR conds return Mon with a couple
more moist systems and flight restrictions possibly affecting the
region as early as Tue.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High  98%     High  97%     High  95%     Med   71%
KGSP       High  84%     High  94%     High 100%     High  85%
KAVL       High 100%     High  98%     High  80%     High  93%
KHKY       High 100%     High  84%     High  83%     High  81%
KGMU       High  81%     High  94%     High  98%     High  93%
KAND       High  94%     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 are available at
the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

SYNOPSIS...PM
NEAR TERM...ARK/SBK
SHORT TERM...PM
LONG TERM...PM
AVIATION...ARK

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
524 AM EDT Sat Mar 27 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-280930-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Alexander-
Iredell-Davie-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Catawba-
Rowan-Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union NC-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Rutherford Mountains-
Greater Rutherford-Polk Mountains-Eastern Polk-Oconee Mountains-
Pickens Mountains-Greenville Mountains-Greater Oconee-
Greater Pickens-Greater Greenville-Spartanburg-Cherokee-York-
Anderson-Abbeville-Laurens-Union SC-Chester-Greenwood-
524 AM EDT Sat Mar 27 2021

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

.DAY ONE...Today and tonight.

Scattered to numerous showers and thunderstorms are expected to
develop across the area today as a warm front lifts north through the
region. A few storms may become severe, with the main threats being
damaging wind gusts and large hail to the size of quarters. There
will also be an isolated tornado threat, mainly across the Piedmont
south of I-40.

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

A line of thunderstorms is expected to cross the area from west to
east during the late morning to mid-afternoon hours. Damaging winds
will be the main threat, but a few storms may produce large hail, as
well.

.SPOTTER INFORMATION STATEMENT...

None.

ARK

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1158 AM EDT Sat Mar 27 2021

NCZ051-058-271700-
Graham NC-Swain NC-
1158 AM EDT Sat Mar 27 2021

...A LINE OF THUNDERSTORMS WITH INTENSE LIGHTNING WILL IMPACT SWAIN
AND GRAHAM COUNTIES UNTIL 100 PM EDT...

At 1156 AM EDT, Doppler radar indicated the leading edge of a line
of thunderstorms with intense lightning along a line extending from
4 miles north of Gatlinburg to 16 miles northwest of Murphy, and
moving east at 40 mph.

Locations to be impacted include...
Bryson City, Robbinsville, Cherokee, Town Of Santeetlah, Smoky
Mountains-Newfound Gap, Smoky Mountains-Fontana Area, Lake
Santeetlah, Smoky Mountains-Balsam Mountain, Fontana Lake and Fontana
Village.

In addition to intense lightning, wind gusts up to 45 mph will be
possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

The combination of gusty winds and saturated soil conditions will
cause scattered trees and power lines to fall. Seek shelter inside an
interior room.

Frequent lightning is occurring with these storms. If outdoors, try
to get indoors or into a hard topped vehicle. Otherwise, stay away
from open areas and isolated high objects such as trees. When
indoors, stay away from windows and doors and avoid using wired
electronic devices. Do not take a shower or bath. Try to unplug
unnecessary appliances before the storms approach.

&&

LAT...LON 3537 8401 3541 8402 3552 8388 3553 8382
      3556 8377 3558 8360 3556 8350 3566 8335
      3567 8329 3557 8316 3547 8332 3547 8334
      3542 8336 3529 8361 3528 8367 3526 8369
      3525 8385 3522 8396 3524 8401 3532 8404
TIME...MOT...LOC 1556Z 268DEG 71KT 3578 8350 3531 8415

SW

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1235 PM EDT Sat Mar 27 2021

NCZ048-052-271730-
Haywood NC-Madison NC-
1235 PM EDT Sat Mar 27 2021

...A CLUSTER OF THUNDERSTORMS WILL IMPACT MADISON AND NORTHERN
HAYWOOD COUNTIES UNTIL 130 PM EDT...

At 1234 PM EDT, Doppler radar indicated the leading edge of a line
of thunderstorms along a line extending from 13 miles southwest of
Erwin to 14 miles southwest of Marshall, and moving east at 40 mph.

Wind gusts up to 40 mph will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

The combination of gusty winds and saturated soil conditions may
cause scattered trees and power lines to fall. Seek shelter inside
an interior room.

&&

LAT...LON 3603 8259 3597 8261 3597 8252 3584 8242
      3573 8267 3570 8285 3568 8289 3564 8287
      3564 8285 3550 8314 3567 8318 3570 8325
      3579 8308 3578 8299 3588 8290 3593 8292
      3595 8285 3593 8281 3600 8277 3606 8263
TIME...MOT...LOC 1634Z 279DEG 148KT 3599 8256 3572 8291

SW