Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
231 PM EDT Mon Jun 21 2021

.SYNOPSIS...
A cold front will bring widespread showers and storms to the region
on Tuesday, before continental high pressure builds in on Wednesday,
causing a drop in temperatures and a lull in active weather.  Over
the weekend, renewed moisture should spur a cycle of diurnal showers
and thunderstorms in advance of a slowly-approaching cold front late
in the forecast period.

&&

.NEAR TERM /THROUGH TUESDAY/...
Convection is having a hard time getting going even within a
developing pre-frontal trof across the mtns and fthills. A
small scale upper ridge is crossing the area which is
maintaining a stg inversion arnd h65. Some showers will likely
get going across the NC mtns with added mech lift and then
expect isol general tstms later this afternoon and evening,
mainly confined to the mtns. Downslope warming will keep the
convec potential quite low to nil outside the mtns this evening.
Min temps will remain a little abv normal as the lower atmos
remains well mixed.

A cold front aided by an anomalous ulvl h5 trof will reach the wrn
NC mtns overnight before sunrise and a few associated tstms may
become quite strong due to enhanced lift and a decent measure of
elCAPE. As the front pushes east thru the day, instability will
remain on the low to moderate side as soundings show deep saturation
and skinny sbCAPE ahead of the line. Nonetheless, bulk shear values
will reach the 30-40 kt range and multicells producing stg outflows
and hail will be likely along and ahead of the front. A few of these
storms could reach severe limits, esp across the NC/SC Piedmont
later in the afternoon during max heating. With the high PWATS ahead
of the boundary, these storms could also produce very good rainfall
rates and localized flooding is possible. The latest NAM lingers the
front over the area thru the evening which is a little
disconcerting, yet most models keep the activity pushing east of the
FA by 00z or so. Max temps Tue will be held about 10 degrees below
normal due to enhance cloud cover and precip.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 145 PM EDT Monday: A 500mb trough axis edges to our east and
lifts out over New England on Wednesday, meaning we'll see minimal
forcing as the height gradient relaxes and winds aloft become nearly
zonal by Thursday.  The frontal boundary settles to our south and
east through Tuesday night, stalling over Georgia and the Atlantic
coast.  Low-end midlevel RHs suggest that precip should be light to
nonexistent by the start of the short-term forecast period for all
but the eastern tier of the CWA.  Can't rule out some patchy rain in
some spots owing to residual low-level moisture, but it should be
low-end as guidance indicates accumulations of less than a quarter
inch past 00Z Wednesday.  This is especially possible in the
mountains, where models may be failing to resolve some low-level
moisture trapped in mountain valleys (in fact, a few models like the
NAMnest and SREF are picking up on this).

In any case, surface flow should veer from northerly to easterly
over the course of the forecast period, acting to introduce a bit of
extra moisture into the profiles on Thursday.  This indicates that
Thursday could see a few more clouds than Wednesday, and perhaps
even an isolated thunderstorm or two.  By and large though,
instability will remain too weak, and profiles too capped, to get
much convective activity going through the afternoon.  Models
continue to trend toward the good moisture remaining well south of
us, so the likelihood of any major impacts on Thursday seems
diminished.

Temps behind the cold front should drop several degrees owing to
strong CAA as the front passes.  So, highs should be a couple
degrees below normal both Wednesday and Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 200 PM EDT Monday: By Thursday night, the surface high will be
sliding off the Atlantic coast, and surface flow will continue to
veer toward a southeasterly WAA regime.  Atlantic moisture will
creep into the Carolinas and introduce an increase in PoPs starting
on Friday.  Consequently, each day this weekend should feature
partly cloudy to mostly cloudy skies, with a potential for pulse
thunderstorms every afternoon.  By Monday, a slowly-propagating
500mb trough over the Midwest begins to impact the region, as
another frontal boundary pushes across the Appalachians.

Temperature advection will remain weak or nonexistent through to the
weekend, when flow off the Atlantic may prompt minimal WAA. However,
the increased cloud cover at this point should counteract any
temperature increase, so highs should remain a few degrees below
normal for the duration of the period.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
At KCLT and elsewhere: An active TAF period is in store for all
terminals. A cold front will work into the NC mtns tonight and push
east thru the day Tue. Expect CIGS to drop to IFR across the mtns and
at KAND before daybreak as a showers and a few tstms develop within
a pre-frontal trof. MVFR CIGS are likely elsewhere, including KCLT.
However, morning fog will not be a factor as sfc winds remain
elevated overnight. Deep convection and tstms should get going
rather early across the mtns and begin affecting KAVL arnd 08z. Have
included PROB30s for TSRA and flight restrictions at all sites to
account for a best chance convective window as the front traverse
east. The front should exit the FA by 00z, however, lingering -shra
and MVFR CIGS will be possible at KCLT thru the late period.

Outlook: Drier weather and mostly VFR conds return to the region for
Wed and Thu. A weak warm front affects the region Fri and Sat, which
will likely bring back flight restrictions.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High  92%     High  89%
KGSP       High 100%     High 100%     High  90%     High  89%
KAVL       High 100%     High 100%     Med   70%     High  89%
KHKY       High 100%     High 100%     High  88%     Med   78%
KGMU       High 100%     High 100%     High  84%     High  87%
KAND       High 100%     High 100%     High  80%     High  87%

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...MPR
NEAR TERM...SBK
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...SBK

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
514 AM EDT Mon Jun 21 2021

GAZ010-017-NCZ033-048>053-058-059-062>065-501-503-505-507-509-
SCZ001>003-220915-
Rabun-Habersham-Avery-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-
Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Caldwell Mountains-Burke Mountains-McDowell Mountains-
Rutherford Mountains-Polk Mountains-Oconee Mountains-
Pickens Mountains-Greenville Mountains-
514 AM EDT Mon Jun 21 2021

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

.DAY ONE...Today and tonight.

Scattered showers and thunderstorms are expected to develop across
the mountains of the Carolinas and northeast Georgia this afternoon.
Storms will become more numerous tonight, as a cold front pushes in
from the west. A few storms may become severe, with damaging wind
gusts the main threat. Also, isolated flash flooding cannot be ruled
out.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed. Please relay any information about
observed severe weather to the NWS while following all local, state,
and CDC guidelines.

GAZ018-026-028-029-NCZ035>037-056-057-068>072-082-502-504-506-508-
510-SCZ004>014-019-220915-
Stephens-Franklin-Hart-Elbert-Alexander-Iredell-Davie-Catawba-Rowan-
Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union NC-
Greater Caldwell-Greater Burke-Eastern McDowell-Greater Rutherford-
Eastern Polk-Greater Oconee-Greater Pickens-Greater Greenville-
Spartanburg-Cherokee-York-Anderson-Abbeville-Laurens-Union SC-
Chester-Greenwood-
514 AM EDT Mon Jun 21 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 showers and thunderstorms may push east from the mountains
into the Piedmont this evening through the overnight tonight. The
main threat will be cloud-to-ground lightning, gusty winds, and
locally heavy rainfall.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

ARK

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
512 PM EDT Mon Jun 21 2021

SCZ004>008-010-212215-
Greater Pickens SC-Cherokee SC-Greater Oconee SC-Anderson SC-
Spartanburg SC-Greater Greenville SC-
512 PM EDT Mon Jun 21 2021

...THUNDERSTORMS WITH TORRENTIAL RAINFALL WILL IMPACT
GREENVILLE...SPARTANBURG...NORTHERN ANDERSON...WEST CENTRAL
CHEROKEE...PICKENS AND OCONEE COUNTIES UNTIL 615 PM EDT...

At 511 PM EDT, Doppler radar indicated thunderstorms with torrential
rainfall along a line extending from 5 miles south of Seneca to 11
miles southeast of Downtown Greenville, and moving northeast at 30
mph.

Locations to be impacted include... Greenville, Spartanburg, Easley,
Clemson, Pickens, Seneca, Greer and Mauldin.

Wind gusts up to 40 mph, pea size hail and very heavy rainfall rates
up to 2 inches per hour 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.

Torrential rainfall may flood areas with poor drainage, such as
ditches and underpasses. Avoid these areas and do not cross flooded
roads. Water levels of small streams may also rise rapidly. Seek
higher ground if threatened by flood waters.

&&

LAT...LON 3454 8308 3487 8276 3504 8161 3475 8212
      3478 8215 3472 8218 3467 8226
TIME...MOT...LOC 2111Z 237DEG 25KT 3461 8294 3471 8230

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