Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 1663
The Storm Prediction Center issued this mesoscale discussion at Aug 31, 2021, 6:57 PM EDT for 18 counties in Virginia; Mercer County, Monroe County, Summers County, West Virginia. It was in force for 93 min.
The area
The outline as issued.
The facts
- Issued
- Aug 31, 2021, 6:57 PM EDT (22:57 UTC)
- Expired
- Aug 31, 2021, 8:30 PM EDT
- In force
- 93 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 21 counties
Bland County, VA, Carroll County, 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, Pulaski County, VA, Roanoke County, VA, Wythe County, VA, Mercer County, WV, Monroe County, WV, Summers County, WV
The radar
The Roanoke radar (KFCX), 31 km from the middle of the area, began a volume at 22:57 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
Roanoke, VA (KRNK), launched 12:00Z, 11.0 hours before the alert went out and 96 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
- 46 J/kg
- Mixed-layer CIN
- -156 J/kg
- Mixed-layer LCL
- 1029 m above ground
- 0-6 km bulk shear
- 30 kt
- 0-1 km storm-relative helicity
- 1 m²/s²
- 0-3 km storm-relative helicity
- 107 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- -0.0
The text
As transmitted.
632
ACUS11 KWNS 312258
SWOMCD
SPC MCD 312257
VAZ000-NCZ000-WVZ000-010030-
Mesoscale Discussion 1663
NWS Storm Prediction Center Norman OK
0557 PM CDT Tue Aug 31 2021
Areas affected...portions of western VA into southern WV
Concerning...Severe potential...Watch possible
Valid 312257Z - 010030Z
Probability of Watch Issuance...40 percent
SUMMARY...A couple of brief tornadoes are possible this evening
across western Virginia into southern West Virginia. Area is being
monitored for possible watch issuance.
DISCUSSION...A couple of cells within a north-south oriented band
lifting northward across western VA have increased in intensity this
evening. Weak to moderate low-level rotation has been noted and one
cell near Blacksburg produced a CC minimum in radar data recently.
This activity is strengthening within a narrow corridor of favorable
low-level shear/SRH. VWP data from KFCX shows an enlarged, curved
low-level hodograph with 0-1 SRH around 200 m2/s2. Furthermore,
effective shear around 30 kt and 0-3 km MLCAPE around 100-150 J/kg
should further support at least briefly organized, rotating cells.
If trends continue, a watch may be needed for portions of the MCD
area this evening.
..Leitman/Edwards.. 08/31/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...RNK...RLX...
LAT...LON 36968131 37448127 37758103 37818075 37848033 37727993
37387971 37047971 36537989 36428029 36448085 36618124
36968131SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 31, 7:36 PM EDT | Tornado Watch | SPC | Albemarle, Alleghany, Amelia, Amherst, Appomattox, Augusta and 49 more | 7 hr |
Nearby
Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in West Virginia, 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.