Alert archive / North Carolina / Mesoscale Discussions in 2021
Mesoscale Discussion 1549
The Storm Prediction Center issued this mesoscale discussion at Aug 17, 2021, 10:04 PM EDT for 26 counties in North Carolina; Cherokee County, York County, South Carolina; 23 counties in Virginia. It was in force for 116 min.
The area
The outline as issued.
The facts
- Issued
- Aug 17, 2021, 10:04 PM EDT (02:04 UTC)
- Expired
- Aug 18, 2021, 12:00 AM EDT
- In force
- 116 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 446
All 51 counties
Alexander County, NC, Alleghany County, NC, Ashe 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, Iredell County, NC, Lincoln County, NC, Mecklenburg County, NC, Montgomery County, NC, Randolph County, NC, Rockingham County, NC, Rowan County, NC, Stanly County, NC, Stokes County, NC, Surry County, NC, Union County, NC, Watauga County, NC, Wilkes County, NC, Yadkin County, NC, Cherokee County, SC, York County, SC, Bedford County, VA, Bland County, VA, Botetourt County, VA, 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, Smyth County, VA, Wythe County, VA
The radar
The Roanoke radar (KFCX), 93 km from the middle of the area, began a volume at 02:05 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 nearest sounding before it
Greensboro/Hi Pt, NC (KGSO), launched 00:00Z, 2.1 hours before the alert went out and 70 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
- 349 J/kg
- Mixed-layer CIN
- -15 J/kg
- Mixed-layer LCL
- 641 m above ground
- 0-6 km bulk shear
- 31 kt
- 0-1 km storm-relative helicity
- 225 m²/s²
- 0-3 km storm-relative helicity
- 278 m²/s²
- Significant tornado parameter
- 0.2
- Supercell composite
- 2.5
The text
As transmitted.
901
ACUS11 KWNS 180204
SWOMCD
SPC MCD 180204
VAZ000-NCZ000-SCZ000-WVZ000-TNZ000-180400-
Mesoscale Discussion 1549
NWS Storm Prediction Center Norman OK
0904 PM CDT Tue Aug 17 2021
Areas affected...western north Carolina and southern virginia
Concerning...Tornado Watch 446...
Valid 180204Z - 180400Z
The severe weather threat for Tornado Watch 446 continues.
SUMMARY...A few tornadoes remain possible across WW462 this evening.
As instability decreases the tornado threat should dampen some
overnight.
DISCUSSION...As of 0150 UTC, regional radar imagery showed a loosely
organized rain band associated with tropical cyclone Fred extending
south through the western Carolinas. Within the band, a mostly
linear convective mode has limited the tornado potential somewhat
over the last couple of hours. The local environment still remain
favorable for updraft rotation and tornadoes with the FCX and TCLT
VADs showing large low-level hodographs and 0-1km SRH greater than
250 m2/s2. While thermodynamically, the loss of diurnal heating has
resulted in decreasing buoyancy, this will be offset somewhat by an
increasingly moist airmass (75+ F dewpoints) associated with the
warm core of Fred. MLCAPE values are generally expected to remain
below 1000 J/kg across upstate North Carolina and southwestern
Virginia, but this should remain adequate to support a few rotating
storms through this evening into southern Virginia.
..Lyons.. 08/18/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...RAH...RNK...CAE...GSP...MRX...
LAT...LON 34868029 34708094 34738137 34998163 35378163 35838168
36288186 36578186 36918171 37128138 37228115 37488066
37697995 37627960 37367928 36937924 36787923 36167946
35477977 34868029SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 18, 2:38 PM EDT | Mesoscale Discussion | SPC | Bertie, Camden, Chowan, Gates, Hertford, Pasquotank and 1 more | 97 min |
| Aug 18, 8:46 AM EDT | Mesoscale Discussion | SPC | Clarke, Fauquier, Loudoun, Prince William, City of Manassas, City of Manassas Park | 119 min |
| Aug 18, 10:58 AM EDT | Mesoscale Discussion | SPC | Arlington, Clarke, Culpeper, Fairfax, Fauquier, Frederick and 15 more | 92 min |
| Aug 18, 11:37 AM EDT | Tornado Watch | SPC | Arlington, Clarke, Culpeper, Fairfax, Fauquier, Frederick and 14 more | 11 hr |
| Aug 18, 3:29 PM EDT | Mesoscale Discussion | SPC | Arlington, Clarke, Fairfax, Frederick, Loudoun, City of Fairfax and 3 more | 91 min |
| Aug 18, 4:57 PM EDT | Mesoscale Discussion | SPC | Arlington, Fairfax, Loudoun, City of Alexandria, City of Fairfax, City of Falls Church | 93 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.