Alert archive / Maryland / Mesoscale Discussions in 2021
Mesoscale Discussion 1669
The Storm Prediction Center issued this mesoscale discussion at Sep 1, 2021, 1:32 PM EDT for 15 counties in Maryland; 7 counties in Virginia. It was in force for 118 min.
The area
The outline as issued.
The facts
- Issued
- Sep 1, 2021, 1:32 PM EDT (17:32 UTC)
- Expired
- Sep 1, 2021, 3:30 PM EDT
- In force
- 118 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 482...483
All 22 counties
Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Cecil County, MD, Charles County, MD, City of Baltimore, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Queen Anne's County, MD, Saint Mary's County, MD, Talbot County, MD, Arlington County, VA, City of Alexandria, VA, City of Falls Church, VA, Essex County, VA, King George County, VA, Richmond County, VA, Westmoreland County, VA
The radar
The Sterling radar (KLWX), 75 km from the middle of the area, began a volume at 17:36 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
Washington/Dulle, VA (KIAD), launched 12:00Z, 5.5 hours before the alert went out and 67 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
- 558 J/kg
- Mixed-layer CIN
- -21 J/kg
- Mixed-layer LCL
- 575 m above ground
- 0-6 km bulk shear
- 48 kt
- 0-1 km storm-relative helicity
- 122 m²/s²
- 0-3 km storm-relative helicity
- 223 m²/s²
- Significant tornado parameter
- 0.4
- Supercell composite
- 2.6
The text
As transmitted.
702
ACUS11 KWNS 011733
SWOMCD
SPC MCD 011732
PAZ000-MDZ000-VAZ000-DCZ000-011930-
Mesoscale Discussion 1669
NWS Storm Prediction Center Norman OK
1232 PM CDT Wed Sep 01 2021
Areas affected...northeast Virginia into central and eastern
Maryland
Concerning...Tornado Watch 482...483...
Valid 011732Z - 011930Z
The severe weather threat for Tornado Watch 482, 483 continues.
SUMMARY...A relative maximum in tornado risk currently stretches
from northeast Virginia into central and eastern Maryland.
DISCUSSION...Multiple supercells have developed within a line south
of the D.C. area, with notable rotation on radar. The moist and
warming air mass has lead to 2000-2500 J/kg SBCAPE, including a
favorable amount of low-level CAPE as 700 mb temperatures remain
tempered.
The 16Z special sounding from IAD shows an impressive low-level
hodograph structure, with observed storm motions resulting in 280
m2/s2 0-1 SRH. As such, it appears RAP-based objective analysis is
underestimating the shear.
The environment east/northeast of the ongoing cells remains
favorable for a supercell tornado threat, bounded on the north by
the stationary front.
..Jewell.. 09/01/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...AKQ...CTP...LWX...
LAT...LON 39747586 39237587 38557604 38147626 37887676 37867701
37977722 38387718 38757720 39277750 39567724 39777654
39827618 39747586SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 1, 12:19 AM EDT | Mesoscale Discussion | SPC | Anne Arundel, Calvert, Charles, Montgomery, Prince George's | 86 min |
| 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, 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 Maryland, 2021Mesoscale Discussions in 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.