Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 341
The Storm Prediction Center issued this mesoscale discussion at Apr 9, 2021, 1:37 PM EDT for 6 counties in North Carolina; 52 counties in Virginia; 4 counties in West Virginia. It was in force for 113 min.
The area
The outline as issued.
The facts
- Issued
- Apr 9, 2021, 1:37 PM EDT (17:37 UTC)
- Expired
- Apr 9, 2021, 3:30 PM EDT
- In force
- 113 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 62 counties
Alleghany County, NC, Ashe County, NC, Stokes County, NC, Surry County, NC, Warren County, NC, Wilkes County, NC, Alleghany County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Augusta County, VA, Bath County, VA, Bedford County, VA, Botetourt County, VA, Brunswick County, VA, Campbell County, VA, Carroll County, VA, Charlotte County, VA, Chesterfield County, VA, City of Buena Vista, VA, City of Colonial Heights, VA, City of Covington, VA, City of Danville, VA, City of Emporia, VA, City of Franklin, VA, City of Galax, VA, City of Hopewell, VA, City of Lexington, VA, City of Martinsville, VA, City of Petersburg, VA, City of Radford, VA, City of Roanoke, VA, City of Salem, VA, City of Staunton, VA, Craig County, VA, Dinwiddie County, VA, Floyd County, VA, Franklin County, VA, Giles County, VA, Grayson County, VA, Greensville County, VA, Halifax County, VA, Henry County, VA, Highland County, VA, Lunenburg County, VA, Mecklenburg County, VA, Montgomery County, VA, Nottoway County, VA, Patrick County, VA, Pittsylvania County, VA, Prince Edward County, VA, Prince George County, VA, Pulaski County, VA, Roanoke County, VA, Rockbridge County, VA, Southampton County, VA, Sussex County, VA, Wythe County, VA, Greenbrier County, WV, Monroe County, WV, Pendleton County, WV, Pocahontas County, WV
The radar
The Roanoke radar (KFCX), 101 km from the middle of the area, began a volume at 17:38 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, 5.6 hours before the alert went out and 31 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
- 132 J/kg
- Mixed-layer CIN
- -77 J/kg
- Mixed-layer LCL
- 654 m above ground
- 0-6 km bulk shear
- 47 kt
- 0-1 km storm-relative helicity
- 182 m²/s²
- 0-3 km storm-relative helicity
- 199 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.2
The text
As transmitted.
663
ACUS11 KWNS 091737
SWOMCD
SPC MCD 091737
VAZ000-NCZ000-WVZ000-TNZ000-091930-
Mesoscale Discussion 0341
NWS Storm Prediction Center Norman OK
1237 PM CDT Fri Apr 09 2021
Areas affected...southeastern West Virginia...southern and western
Virginia...and northern North Carolina
Concerning...Severe potential...Watch possible
Valid 091737Z - 091930Z
Probability of Watch Issuance...40 percent
SUMMARY...Severe risk -- including potential for locally damaging
winds, and possibly a tornado or two -- is expected to increase
gradually over the next couple of hours. A WW may eventually be
needed.
DISCUSSION...Visible satellite imagery shows low clouds that remain
slow to erode east of the Appalachian crest, and north of a
west-to-east remnant damming front in the vicinity of the North
Carolina-Virginia border. Near and south of this boundary, and
westward along the higher terrain, diurnal heating has pushed
mixed-layer CAPE values to around 1000 J/kg. This is supporting an
increase in TCU/CB from eastern West Virginia southward to far
western North Carolina, along with expanding, shallower cumulus
eastward in the vicinity of the aforementioned front.
With time, a continued increase in convection is expected. Aided by
favorable low-level and deep-layer shear -- particularly near and
just north of the front -- a few stronger storms will likely evolve,
including potential for a supercell or two. The latest CAM output
suggests that severe risk should begin to ramp up between 19Z and
20Z, which seems consistent with the gradually evolving CU field.
Risk should remain rather short-lived over western portions of the
area, with storms weakening as they shift off the higher terrain and
atop the more stable boundary layer. Risk may linger into the
evening, however, across the southern Virginia area along the
remnant front.
..Goss.. 04/09/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...AKQ...LWX...RAH...RNK...PBZ...RLX...MRX...
LAT...LON 39027935 38707888 37747900 37397921 37397845 37397740
37017673 36477670 36377826 36438008 36078121 36448176
36938119 38018066 39027935SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 9, 3:38 PM EDT | Severe Thunderstorm Watch | SPC | Bertie, Camden, Caswell, Chowan, Edgecombe, Franklin and 14 more | 7 hr |
| Apr 9, 6:23 PM EDT | Mesoscale Discussion | SPC | Bertie, Camden, Caswell, Chowan, Currituck, Edgecombe and 14 more | 97 min |
Nearby
Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in North Carolina, 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.