Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 847
The Storm Prediction Center issued this mesoscale discussion at Jun 4, 2021, 12:46 PM EDT for 8 counties in Maryland; 26 counties in Virginia. It was in force for 59 min.
The area
The outline as issued.
The facts
- Issued
- Jun 4, 2021, 12:46 PM EDT (16:46 UTC)
- Expired
- Jun 4, 2021, 1:45 PM EDT
- In force
- 59 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch likely
- Chance of a watch
- 80%
All 34 counties
Anne Arundel County, MD, Calvert County, MD, Charles County, MD, City of Baltimore, MD, Prince George's County, MD, Queen Anne's County, MD, Saint Mary's County, MD, Talbot County, MD, Amelia County, VA, Arlington County, VA, Caroline County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Richmond, VA, Cumberland County, VA, Essex County, VA, Fairfax County, VA, Fluvanna County, VA, Goochland County, VA, Hanover County, VA, King George County, VA, King William County, VA, Louisa County, VA, Orange County, VA, Powhatan County, VA, Prince William County, VA, Richmond County, VA, Spotsylvania County, VA, Stafford County, VA, Westmoreland County, VA
The radar
The Sterling radar (KLWX), 95 km from the middle of the area, began a volume at 16:46 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
Washington/Dulle, VA (KIAD), launched 12:00Z, 4.8 hours before the alert went out and 92 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
- 381 J/kg
- Mixed-layer CIN
- -55 J/kg
- Mixed-layer LCL
- 947 m above ground
- 0-6 km bulk shear
- 42 kt
- 0-1 km storm-relative helicity
- -8 m²/s²
- 0-3 km storm-relative helicity
- 73 m²/s²
- Significant tornado parameter
- -0.0
- Supercell composite
- -0.1
The text
As transmitted.
023
ACUS11 KWNS 041647
SWOMCD
SPC MCD 041646
MDZ000-VAZ000-DCZ000-041745-
Mesoscale Discussion 0847
NWS Storm Prediction Center Norman OK
1146 AM CDT Fri Jun 04 2021
Areas affected...portions of Virginia into portions of the
Chesapeake/Delmarva
Concerning...Severe potential...Watch likely
Valid 041646Z - 041745Z
Probability of Watch Issuance...80 percent
SUMMARY...A few stronger storms capable of minor damage will require
WW issuance.
DISCUSSION...Daytime heating in the wake of an eastward-moving band
of high cloud cover has permitted 1000 J/kg mixed-layer CAPE to
evolve over central and eastern Virginia. A band of thunderstorms
has begun to develop in response, near a surface convergence axis
aligned northeast-to-southwest across the area.
With largely unidirectional west-northwesterly flow across the area
increasing to 30 to 40 kt at mid levels, small bands of quick-moving
storms will likely evolve, along with attendant risk for a few
stronger winds gusts capable of minor damage.
..Goss/Guyer.. 06/04/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...AKQ...LWX...RNK...
LAT...LON 37487855 38467791 39477644 38927582 37927650 37157819
37487855SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jun 4, 12:59 PM EDT | Severe Thunderstorm Watch | SPC | Calvert, Charles, Dorchester, Saint Mary's, Somerset, Wicomico | 7 hr |
| Jun 4, 2:26 PM EDT | Mesoscale Discussion | SPC | Cecil, Harford | 94 min |
| Jun 4, 4:12 PM EDT | Mesoscale Discussion | SPC | Calvert, Caroline, Cecil, Dorchester, Harford, Kent and 6 more | 93 min |
Nearby
Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in Maryland, 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.