Alert archive / Virginia / Mesoscale Discussions in 2020

Mesoscale Discussion 820

June 4, 20204 states

The Storm Prediction Center issued this mesoscale discussion at Jun 4, 2020, 4:41 PM EDT for 4 states. It was in force for 94 min.

The area

The outline as issued.

The facts

Issued: Jun 4, 2020, 4:41 PM EDT (20:41 UTC)
Expired: Jun 4, 2020, 6:15 PM EDT
In force: 94 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 250

All 69 counties

Allegany County, MD, Baltimore County, MD, Carroll County, MD, Frederick County, MD, Garrett County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Washington County, MD, Adams County, PA, Bedford County, PA, Blair County, PA, Cambria County, PA, Centre County, PA, Clinton County, PA, Columbia County, PA, Cumberland County, PA, Dauphin County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Juniata County, PA, Lebanon County, PA, Mifflin County, PA, Montour County, PA, Northumberland County, PA, Perry County, PA, Snyder County, PA, Somerset County, PA, Union County, PA, York County, PA, Albemarle County, VA, Arlington County, VA, Augusta County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Harrisonburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Staunton, VA, City of Waynesboro, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Frederick County, VA, Greene County, VA, Highland County, VA, Loudoun County, VA, Madison County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Rockingham County, VA, Shenandoah County, VA, Warren County, VA, Berkeley County, WV, Grant County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV, Pendleton County, WV

The radar

The Sterling radar (KLWX), 110 km from the middle of the area, began a volume at 20:42 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, 8.7 hours before the alert went out and 116 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: 139 J/kg
Mixed-layer CIN: -204 J/kg
Mixed-layer LCL: 1499 m above ground
0-6 km bulk shear: 41 kt
0-1 km storm-relative helicity: -64 m²/s²
0-3 km storm-relative helicity: 54 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.0

Open this sounding in Storm Lab

The text

As transmitted.

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SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 4, 2:02 PM EDT	Mesoscale Discussion	SPC	Baltimore, Carroll, Charles, Frederick, Howard, Montgomery and 2 more	118 min
Jun 4, 2:29 PM EDT	Severe Thunderstorm Watch	SPC	Allegany, Anne Arundel, Baltimore, Carroll, Frederick, Harford and 5 more	8 hr
Jun 4, 12:45 PM EDT	Mesoscale Discussion	SPC	Allegheny, Armstrong, Beaver, Butler, Clarion, Fayette and 5 more	90 min
Jun 4, 12:55 PM EDT	Severe Thunderstorm Watch	SPC	Allegheny, Armstrong, Beaver, Butler, Clarion, Fayette and 6 more	6 hr
Jun 4, 2:14 PM EDT	Mesoscale Discussion	SPC	Beaver, Lawrence, Washington	61 min
Jun 4, 4:00 PM EDT	Mesoscale Discussion	SPC	Allegheny, Armstrong, Beaver, Butler, Clarion, Greene and 4 more	90 min
Jun 4, 6:44 PM EDT	Mesoscale Discussion	SPC	Adams, Bedford, Berks, Blair, Centre, Chester and 19 more	91 min

Nearby

Mesoscale Discussions in Virginia, 2020 Mesoscale Discussions in Pennsylvania, 2020 Mesoscale Discussions in Maryland, 2020 Every mesoscale discussion in 2020

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.