Alert archive / Virginia / Mesoscale Discussions in 2018

Mesoscale Discussion 1339

August 21, 20184 states

The Storm Prediction Center issued this mesoscale discussion at Aug 21, 2018, 7:06 PM EDT for 4 states. It was in force for 84 min.

The area

The outline as issued.

The facts

Issued: Aug 21, 2018, 7:06 PM EDT (23:06 UTC)
Expired: Aug 21, 2018, 8:30 PM EDT
In force: 84 min
Issued by: the Storm Prediction Center

All 54 counties

Anne Arundel County, MD, Baltimore County, MD, Carroll County, MD, Cecil 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, Washington County, MD, Adams County, PA, Berks County, PA, Chester County, PA, Cumberland County, PA, Dauphin County, PA, Franklin County, PA, Juniata County, PA, Lancaster County, PA, Lebanon County, PA, Perry County, PA, York County, PA, Arlington County, VA, City of Alexandria, 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 Winchester, VA, Clarke County, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Frederick County, VA, Loudoun County, VA, Madison County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Rockingham County, VA, Shenandoah County, VA, Stafford 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), 66 km from the middle of the area, began a volume at 23:10 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, 11.1 hours before the alert went out and 71 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: 187 J/kg
Mixed-layer CIN: -22 J/kg
Mixed-layer LCL: 597 m above ground
0-6 km bulk shear: 32 kt
0-1 km storm-relative helicity: 122 m²/s²
0-3 km storm-relative helicity: 183 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 0.6

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
Aug 21, 2:16 PM EDT	Mesoscale Discussion	SPC	Allegany, Garrett	119 min
Aug 21, 2:41 PM EDT	Severe Thunderstorm Watch	SPC	Allegany, Carroll, Frederick, Garrett, Washington	7 hr
Aug 21, 4:56 PM EDT	Mesoscale Discussion	SPC	Allegany, Carroll, Frederick, Garrett, Montgomery, Washington	2 hr
Aug 21, 5:03 PM EDT	Mesoscale Discussion	SPC	Charles, Saint Mary's	117 min
Aug 21, 12:45 PM EDT	Mesoscale Discussion	SPC	Fayette, Greene, Washington, Westmoreland	3 hr

Nearby

Mesoscale Discussions in Virginia, 2018 Mesoscale Discussions in Maryland, 2018 Mesoscale Discussions in Pennsylvania, 2018 Every mesoscale discussion in 2018

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.