Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 1666
The Storm Prediction Center issued this mesoscale discussion at Sep 1, 2021, 12:19 AM EDT for 5 counties in Maryland; 14 counties in Virginia. It was in force for 86 min.
The area
The outline as issued.
The facts
- Issued
- Sep 1, 2021, 12:19 AM EDT (04:19 UTC)
- Expired
- Sep 1, 2021, 1:45 AM EDT
- In force
- 86 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
Counties Anne Arundel County, MD, Calvert County, MD, Charles County, MD, Montgomery County, MD, Prince George's County, MD, Arlington 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, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, King George County, VA, Loudoun County, VA, Prince William County, VA, Stafford County, VA
The radar
The Sterling radar (KLWX), 51 km from the middle of the area, began a volume at 04:19 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 00:00Z, 4.3 hours before the alert went out and 45 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
- 723 J/kg
- Mixed-layer CIN
- -24 J/kg
- Mixed-layer LCL
- 969 m above ground
- 0-6 km bulk shear
- 32 kt
- 0-1 km storm-relative helicity
- 96 m²/s²
- 0-3 km storm-relative helicity
- 171 m²/s²
- Significant tornado parameter
- 0.3
- Supercell composite
- 2.7
The text
As transmitted.
144
ACUS11 KWNS 010420
SWOMCD
SPC MCD 010419
MDZ000-VAZ000-DCZ000-010545-
Mesoscale Discussion 1666
NWS Storm Prediction Center Norman OK
1119 PM CDT Tue Aug 31 2021
Areas affected...northern VA into MD
Concerning...Severe potential...Watch possible
Valid 010419Z - 010545Z
Probability of Watch Issuance...40 percent
SUMMARY...A couple of strong cells capable of producing brief
tornadoes may spread northeast across parts of northern Virginia and
western Maryland.
DISCUSSION...A few persistent cells across central VA continue to
show periods of low-level rotation as they track along the gradient
of stronger 0-3 km MLCAPE. Forecast guidance shows this area of
relatively greater instability persisting over parts of northern VA
and MD. Low-level shear currently is weak downstream from WW 480
across the MCD area. However, some improvement is forecast as
stronger ascent spreads over the region and the stalled surface
boundary lifts northward. This could support a few stronger cells
with a continued tornado threat into the overnight hours, and a
downstream tornado watch is possible.
..Leitman/Edwards.. 09/01/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...AKQ...LWX...
LAT...LON 38107736 38247777 38587810 38727809 38917804 39217755
39257674 39067630 38707626 38357635 38197667 38127701
38107736SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 1, 12:56 AM EDT | Tornado Watch | SPC | Anne Arundel, Baltimore, Carroll, Charles, Frederick, Harford and 4 more | 6 hr |
| Sep 1, 4:01 AM EDT | Mesoscale Discussion | SPC | Anne Arundel, Baltimore, Carroll, Cecil, Harford, Howard and 4 more | 119 min |
| Sep 1, 11:03 AM EDT | Mesoscale Discussion | SPC | Anne Arundel, Baltimore, Calvert, Caroline, Carroll, Cecil and 14 more | 2 hr |
| Sep 1, 11:46 AM EDT | Tornado Watch | SPC | Anne Arundel, Baltimore, Calvert, Carroll, Cecil, Charles and 11 more | 9 hr |
| Sep 1, 12:40 PM EDT | Tornado Watch | SPC | Caroline, Kent, Queen Anne's, Talbot | 9 hr |
| Sep 1, 1:32 PM EDT | Mesoscale Discussion | SPC | Anne Arundel, Baltimore, Calvert, Carroll, Cecil, Charles and 9 more | 118 min |
| Sep 1, 3:09 PM EDT | Mesoscale Discussion | SPC | Caroline, Cecil, Dorchester, Harford, Kent, Queen Anne's and 2 more | 3 hr |
| Aug 31, 11:01 PM EDT | Mesoscale Discussion | SPC | Albemarle, Amherst, Augusta, Bath, Botetourt, Culpeper and 15 more | 89 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.