Alert archive / Virginia / Mesoscale Discussions in 2015

Mesoscale Discussion 402

April 20, 20155 states

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2015, 5:01 PM EDT for 5 states. It was in force for 119 min.

The area

The outline as issued.

The facts

Issued: Apr 20, 2015, 5:01 PM EDT (21:01 UTC)
Expired: Apr 20, 2015, 7:00 PM EDT
In force: 119 min
Issued by: the Storm Prediction Center

All 77 counties

New Castle County, DE, Allegany County, MD, 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, Talbot County, MD, Washington County, MD, Adams County, PA, Bedford County, PA, Berks County, PA, Blair County, PA, Chester County, PA, Cumberland County, PA, Dauphin County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Juniata County, PA, Lancaster County, PA, Lebanon County, PA, Montgomery County, PA, Perry County, PA, York County, PA, Albemarle County, VA, Arlington County, VA, Augusta County, VA, Caroline 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, Frederick County, VA, Greene County, VA, King George County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Orange County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Rockingham County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA, Westmoreland County, VA, Berkeley County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV

The radar

The Sterling radar (KLWX), 28 km from the middle of the area, began a volume at 21:01 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, 9.0 hours before the alert went out and 21 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 694 m above ground
0-6 km bulk shear: 55 kt
0-1 km storm-relative helicity: 166 m²/s²
0-3 km storm-relative helicity: 205 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

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 20, 3:08 PM EDT	Tornado Watch	SPC	Kent, New Castle	9 hr
Apr 20, 1:54 PM EDT	Mesoscale Discussion	SPC	Allegany, Anne Arundel, Baltimore, Carroll, Charles, Frederick and 6 more	3 hr
Apr 20, 3:23 PM EDT	Mesoscale Discussion	SPC	Bradford, Cameron, Centre, Clearfield, Clinton, Elk and 8 more	2 hr
Apr 20, 5:57 PM EDT	Mesoscale Discussion	SPC	Bradford, Cameron, Centre, Clinton, Columbia, Luzerne and 9 more	2 hr
Apr 20, 7:31 PM EDT	Mesoscale Discussion	SPC	Lackawanna, Susquehanna, Wayne	2 hr
Apr 20, 7:56 PM EDT	Severe Thunderstorm Watch	SPC	Bradford, Carbon, Lackawanna, Luzerne, Monroe, Northampton and 4 more	4 hr
Apr 20, 2:25 AM EDT	Mesoscale Discussion	SPC	Isle of Wight, Southampton, City of Chesapeake, City of Franklin, City of Hampton, City of Norfolk and 2 more	95 min
Apr 20, 2:55 PM EDT	Severe Thunderstorm Watch	SPC	Alleghany, Amelia, Amherst, Appomattox, Bath, Bedford and 77 more	7 hr
Apr 20, 6:27 PM EDT	Mesoscale Discussion	SPC	Amelia, Appomattox, Bedford, Brunswick, Buckingham, Campbell and 50 more	93 min

Nearby

Mesoscale Discussions in Virginia, 2015 Mesoscale Discussions in Maryland, 2015 Mesoscale Discussions in Pennsylvania, 2015 Every mesoscale discussion in 2015

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.