Alert archive / North Carolina / Mesoscale Discussions in 2021
Mesoscale Discussion 1548
The Storm Prediction Center issued this mesoscale discussion at Aug 17, 2021, 5:55 PM EDT for 34 counties in North Carolina; 13 counties in South Carolina; 19 counties in Virginia. It was in force for 65 min.
The area
The outline as issued.
The facts
- Issued
- Aug 17, 2021, 5:55 PM EDT (21:55 UTC)
- Expired
- Aug 17, 2021, 7:00 PM EDT
- In force
- 65 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...tornado watch likely 444...445
- Chance of a watch
- 95%
All 66 counties
Alexander County, NC, Alleghany County, NC, Ashe County, NC, Avery County, NC, Buncombe County, NC, Burke County, NC, Cabarrus County, NC, Caldwell County, NC, Catawba County, NC, Cleveland County, NC, Davidson County, NC, Davie County, NC, Forsyth County, NC, Gaston County, NC, Guilford County, NC, Henderson County, NC, Iredell County, NC, Lincoln County, NC, McDowell County, NC, Mecklenburg County, NC, Mitchell County, NC, Polk County, NC, Randolph County, NC, Rockingham County, NC, Rowan County, NC, Rutherford County, NC, Stanly County, NC, Stokes County, NC, Surry County, NC, Union County, NC, Watauga County, NC, Wilkes County, NC, Yadkin County, NC, Yancey County, NC, Cherokee County, SC, Chester County, SC, Edgefield County, SC, Fairfield County, SC, Greenville County, SC, Greenwood County, SC, Lancaster County, SC, Laurens County, SC, Newberry County, SC, Saluda County, SC, Spartanburg County, SC, Union County, SC, York County, SC, Carroll County, VA, City of Danville, VA, City of Galax, VA, City of Martinsville, VA, City of Radford, VA, City of Roanoke, VA, City of Salem, VA, Craig County, VA, Floyd County, VA, Franklin County, VA, Giles County, VA, Grayson County, VA, Henry County, VA, Montgomery County, VA, Patrick County, VA, Pittsylvania County, VA, Pulaski County, VA, Roanoke County, VA, Wythe County, VA
The radar
The Greer radar (KGSP), 124 km from the middle of the area, began a volume at 21:58 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, 9.9 hours before the alert went out and 126 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.
803
ACUS11 KWNS 172155
SWOMCD
SPC MCD 172155
VAZ000-NCZ000-SCZ000-WVZ000-TNZ000-172300-
Mesoscale Discussion 1548
NWS Storm Prediction Center Norman OK
0455 PM CDT Tue Aug 17 2021
Areas affected...Western Carolinas and southwest Virginia
Concerning...Severe potential...Tornado Watch likely 444...445...
Valid 172155Z - 172300Z
Probability of Watch Issuance...95 percent
SUMMARY...The threat for a few tornadoes is expected to persist this
evening and overnight as Tropical depression Fred continues north.
Replacement tornado watches are forthcoming.
DISCUSSION...Latest track guidance from WPC placed the center of
Tropical Depression Fred at 34.7N 83.9W, or about 90 miles WSW of
Asheville, NC. Along Fred's southeastern flank, multiple bands and
clusters of low-topped supercells have produced several reported
tornadoes over the last couple of hours. As Fred continues northward
across the western Carolinas, the environment is forecast to remain
favorable for additional tornadoes this evening, and possibly
overnight. SPC mesoanalysis and regional VAD wind profiles depict a
corridor of strong low-level shear with 0-1km in excess of 200 m2/s2
from northwestern South Carolina to southwestern Virginia. While
buoyancy is not overly strong, cloud breaks and tropical dewpoints
near 75 F are supporting tall and skinny CAPE profiles with MLCAPE
around 500-1000 J/kg. The combination of instability and low-level
shear will continue to support a risk for mini-supercells with
damaging wind gusts and tornadoes across the western Carolinas and
southwestern Virginia this evening. A new Tornado Watch will be
coordinated shortly ahead of the 23 UTC expiration of WW444 and
WW445.
..Lyons/Thompson.. 08/17/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...RAH...RNK...CAE...GSP...MRX...
LAT...LON 35758252 36338193 36708139 37128110 37368080 37508029
37317971 36937939 36527941 35977960 35457986 35148011
34858042 34628069 34328095 33778173 33728212 33878227
34208230 34688245 35368264 35598270 35758252SPC 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, 3:25 PM EDT | Mesoscale Discussion | SPC | Buncombe, Burke, Cleveland, Gaston, Henderson, Lincoln and 4 more | 2 hr |
| 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 North Carolina, 2021Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in South 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.