Alert archive / Virginia / Mesoscale Discussions in 2011

Mesoscale Discussion 631

April 27, 201116 counties in Maryland; 37 counties in Virginia; 8 counties in West Virginia

The Storm Prediction Center issued this mesoscale discussion at Apr 27, 2011, 4:39 PM EDT for 16 counties in Maryland; 37 counties in Virginia; 8 counties in West Virginia. It was in force for 66 min.

The area

The outline as issued.

The facts

Issued: Apr 27, 2011, 4:39 PM EDT (20:39 UTC)
Expired: Apr 27, 2011, 5:45 PM EDT
In force: 66 min
Issued by: the Storm Prediction Center

All 61 counties

Allegany County, MD, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Somerset County, MD, Talbot County, MD, Washington County, MD, 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 Fredericksburg, 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, Fluvanna County, VA, Frederick County, VA, Goochland County, VA, Greene County, VA, Highland County, VA, King George County, VA, Loudoun County, VA, Louisa 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, Spotsylvania 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), 63 km from the middle of the area, began a volume at 20:39 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 12:00Z, 8.7 hours before the alert went out and 57 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: 215 J/kg
Mixed-layer CIN: -75 J/kg
Mixed-layer LCL: 636 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 123 m²/s²
0-3 km storm-relative helicity: 150 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 0.8

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

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SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 27, 1:23 PM EDT	Tornado Watch	SPC	Allegany, Anne Arundel, Baltimore, Calvert, Carroll, Charles and 8 more	5 hr
Apr 27, 1:24 PM EDT	Mesoscale Discussion	SPC	Allegany, Garrett	96 min
Apr 27, 3:10 PM EDT	Tornado Watch	SPC	Garrett	7 hr
Apr 27, 3:55 PM EDT	Mesoscale Discussion	SPC	Caroline, Cecil, Dorchester, Harford, Kent, Queen Anne's and 3 more	65 min
Apr 27, 6:00 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Calvert, Carroll, Charles, Frederick and 9 more	60 min
Apr 27, 6:15 PM EDT	Tornado Watch	SPC	Allegany, Anne Arundel, Baltimore, Calvert, Carroll, Charles and 8 more	6 hr
Apr 27, 6:50 PM EDT	Mesoscale Discussion	SPC	Carroll, Harford, Washington	55 min
Apr 27, 7:55 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Calvert, Carroll, Charles, Harford and 8 more	65 min
Apr 27, 8:34 AM EDT	Tornado Watch	SPC	Lee	4 hr
Apr 27, 12:51 PM EDT	Mesoscale Discussion	SPC	Albemarle, Amelia, Amherst, Appomattox, Bedford, Brunswick and 49 more	84 min
Apr 27, 3:22 PM EDT	Mesoscale Discussion	SPC	Bland, Buchanan, Dickenson, Grayson, Lee, Russell and 9 more	83 min
Apr 27, 5:38 PM EDT	Mesoscale Discussion	SPC	Buchanan, Dickenson, Lee, Russell, Scott, Wise and 1 more	37 min
Apr 27, 5:44 PM EDT	Tornado Watch	SPC	Buchanan, Dickenson, Lee, Russell, Scott, Smyth and 5 more	7 hr
Apr 27, 9:39 AM EDT	Mesoscale Discussion	SPC	Cabell, Calhoun, Jackson, Kanawha, Lincoln, Mason and 7 more	66 min

Nearby

Mesoscale Discussions in Virginia, 2011 Mesoscale Discussions in Maryland, 2011 Mesoscale Discussions in West Virginia, 2011 Every mesoscale discussion in 2011

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.