Alert archive / Virginia / Mesoscale Discussions in 2021

Mesoscale Discussion 1484

August 11, 202115 counties in Maryland; 59 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Aug 11, 2021, 3:47 PM EDT for 15 counties in Maryland; 59 counties in Virginia. It was in force for 88 min.

The area

The outline as issued.

The facts

Issued: Aug 11, 2021, 3:47 PM EDT (19:47 UTC)
Expired: Aug 11, 2021, 5:15 PM EDT
In force: 88 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 425

All 74 counties

Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Cecil County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, 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, Albemarle County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Bedford County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Colonial Heights, VA, City of Danville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Hopewell, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Martinsville, VA, City of Petersburg, VA, City of Richmond, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Goochland County, VA, Greene County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Loudoun County, VA, Louisa County, VA, Lunenburg County, VA, Madison County, VA, Mecklenburg County, VA, Nelson County, VA, New Kent County, VA, Nottoway County, VA, Orange County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Spotsylvania County, VA, Stafford County, VA, Westmoreland County, VA

The radar

The Sterling radar (KLWX), 100 km from the middle of the area, began a volume at 19:50 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, 7.8 hours before the alert went out and 100 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 553 J/kg
Mixed-layer CIN: -190 J/kg
Mixed-layer LCL: 1301 m above ground
0-6 km bulk shear: 13 kt
0-1 km storm-relative helicity: 20 m²/s²
0-3 km storm-relative helicity: 77 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

917 
ACUS11 KWNS 111948
SWOMCD
SPC MCD 111947 
MDZ000-VAZ000-PAZ000-DCZ000-WVZ000-112115-

Mesoscale Discussion 1484
NWS Storm Prediction Center Norman OK
0247 PM CDT Wed Aug 11 2021

Areas affected...Portions of Virginia and Maryland

Concerning...Severe Thunderstorm Watch 425...

Valid 111947Z - 112115Z

The severe weather threat for Severe Thunderstorm Watch 425
continues.

SUMMARY...An isolated damaging wind gust threat continues across
portions of Virginia and Maryland.

DISCUSSION...A broken line of storms has moved off of the higher
terrain and is moving toward the I-95 corridor. Thus far damaging
wind reports have been isolated and sporadic. However, storms have
been in weaker instability and are now moving into a region with low
70s dewpoints and 2000+ J/kg MLCAPE. Therefore, expect additional
storm development and the potential for clustering which could bring
a more concentrated severe wind threat. Otherwise, pulse type
updraft-downdraft pairs should continue to produce isolated wind
damage.

..Bentley.. 08/11/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...PHI...AKQ...CTP...LWX...RNK...

LAT...LON   39467772 39747702 39697586 38087641 37257711 37017777
            36577851 36567995 37077979 38467846 39467772

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 11, 1:01 PM EDT	Mesoscale Discussion	SPC	Carroll, Charles, Frederick, Howard, Montgomery, Prince George's and 1 more	89 min
Aug 11, 2:02 PM EDT	Severe Thunderstorm Watch	SPC	Allegany, Anne Arundel, Baltimore, Calvert, Carroll, Cecil and 9 more	6 hr
Aug 11, 3:02 PM EDT	Severe Thunderstorm Watch	SPC	Caroline, Kent, Queen Anne's, Talbot	6 hr
Aug 11, 6:44 PM EDT	Mesoscale Discussion	SPC	Cecil	91 min

Nearby

Mesoscale Discussions in Virginia, 2021 Mesoscale Discussions in Maryland, 2021 Every 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.