Alert archive / South Carolina / Mesoscale Discussions in 2021
Mesoscale Discussion 1546
The Storm Prediction Center issued this mesoscale discussion at Aug 17, 2021, 3:25 PM EDT for 10 counties in North Carolina; 12 counties in South Carolina. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 17, 2021, 3:25 PM EDT (19:25 UTC)
- Expired
- Aug 17, 2021, 5:30 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 444...445
All 22 counties
Buncombe County, NC, Burke County, NC, Cleveland County, NC, Gaston County, NC, Henderson County, NC, Lincoln County, NC, McDowell County, NC, Polk County, NC, Rutherford County, NC, Transylvania County, NC, Cherokee County, SC, Chester County, SC, Fairfield County, SC, Greenville County, SC, Laurens County, SC, Lexington County, SC, Newberry County, SC, Pickens County, SC, Saluda County, SC, Spartanburg County, SC, Union County, SC, York County, SC
The radar
The Greer radar (KGSP), 38 km from the middle of the area, began a volume at 19:29 UTC, the scan nearest the moment this went out.
Open the radar archive at this moment
The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.
The watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Greensboro/Hi Pt, NC (KGSO), launched 12:00Z, 7.4 hours before the alert went out and 228 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 522 J/kg
- Mixed-layer CIN
- -5 J/kg
- Mixed-layer LCL
- 593 m above ground
- 0-6 km bulk shear
- 26 kt
- 0-1 km storm-relative helicity
- 77 m²/s²
- 0-3 km storm-relative helicity
- 99 m²/s²
- Significant tornado parameter
- 0.1
- Supercell composite
- 0.9
The text
As transmitted.
306
ACUS11 KWNS 171925
SWOMCD
SPC MCD 171925
SCZ000-NCZ000-GAZ000-172130-
Mesoscale Discussion 1546
NWS Storm Prediction Center Norman OK
0225 PM CDT Tue Aug 17 2021
Areas affected...Northwestern South Carolina and adjacent areas of
North Carolina
Concerning...Tornado Watch 444...445...
Valid 171925Z - 172130Z
The severe weather threat for Tornado Watch 444, 445 continues.
SUMMARY...The tornado threat continues across both WW 444 and 445,
though the area of highest tornado potential over the next 1-2 hours
will likely reside over northwestern South Carolina and adjacent
areas of North Carolina.
DISCUSSION...The environment over central to northwestern SC has
been very productive for tornado generation over the past few hours
despite the continued weakening of the remnants of TS Fred. This is
likely attributable to a combination of higher low-level theta-e
advection from the central Carolinas (where breaks in cloud cover
have allowed temperatures to warm into the mid 80s), continued
confluence along a residual rain band, and a persistent corridor of
warm air advection between 925-850 mb from central to northwestern
SC on the eastern side of the tropical low. In addition to providing
lift and maintaining instability, this warm advection is supporting
150-250 m2/s2 of 0-1 km SRH, as observed by regional VWPs. This
favorable environment is expected to be maintained through the late
afternoon hours, which suggests that the associated tornado threat
will persist as well - primarily along and north of the I-26
Corridor in northwestern SC and into western portions of NC. An
upgrade to an Enhanced risk is planned for parts of this region for
the 20z Convective outlook.
..Moore.. 08/17/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CAE...GSP...
LAT...LON 33618159 34318212 34728272 34908311 35248316 35518285
35878210 35768152 35428110 35048089 34688087 34308082
33718112 33618159SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 17, 10:42 AM EDT | Tornado Watch | SPC | Alexander, Avery, Buncombe, Burke, Cabarrus, Caldwell and 20 more | 8 hr |
| Aug 17, 12:35 PM EDT | Mesoscale Discussion | SPC | Alexander, Cabarrus, Catawba, Cleveland, Davie, Forsyth and 9 more | 85 min |
| Aug 17, 1:06 PM EDT | Tornado Watch | SPC | Alleghany, Ashe, Rockingham, Stokes, Surry, Watauga and 2 more | 5 hr |
| Aug 17, 5:55 PM EDT | Mesoscale Discussion | SPC | Alexander, Alleghany, Ashe, Avery, Buncombe, Burke and 28 more | 65 min |
| Aug 17, 6:28 PM EDT | Tornado Watch | SPC | Alexander, Alleghany, Ashe, Avery, Buncombe, Burke and 24 more | 10 hr |
| Aug 17, 8:22 AM EDT | Mesoscale Discussion | SPC | Abbeville, Anderson, Edgefield, Greenwood, McCormick | 113 min |
Nearby
Mesoscale Discussions in South Carolina, 2021Mesoscale Discussions in North Carolina, 2021Every mesoscale discussion in 2021
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.