Alert archive / Virginia / Mesoscale Discussions in 2015

Mesoscale Discussion 397

April 20, 20155 states

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2015, 1:54 PM EDT for 5 states. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued
Apr 20, 2015, 1:54 PM EDT (17:54 UTC)
Expired
Apr 20, 2015, 4:30 PM EDT
In force
3 hr
Issued by
the Storm Prediction Center
Chance of a watch
80%
All 107 counties

Allegany County, MD, Anne Arundel County, MD, Baltimore 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, Washington County, MD, Alleghany County, NC, Stokes County, NC, Surry County, NC, Adams County, PA, Bedford County, PA, Cumberland County, PA, Franklin County, PA, Fulton County, PA, Lancaster County, PA, York County, PA, Albemarle County, VA, Alleghany County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Augusta County, VA, Bath County, VA, Bedford County, VA, Bland County, VA, Botetourt County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, Carroll County, VA, Charlotte County, VA, City of Alexandria, VA, City of Buena Vista, VA, City of Charlottesville, VA, City of Covington, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Galax, VA, City of Harrisonburg, VA, City of Lexington, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Martinsville, VA, City of Radford, VA, City of Roanoke, VA, City of Salem, VA, City of Staunton, VA, City of Waynesboro, VA, City of Winchester, VA, Clarke County, VA, Craig County, VA, Culpeper County, VA, Cumberland County, VA, Fairfax County, VA, Fauquier County, VA, Floyd County, VA, Fluvanna County, VA, Franklin County, VA, Frederick County, VA, Giles County, VA, Goochland County, VA, Grayson County, VA, Greene County, VA, Henry County, VA, Highland County, VA, King George County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Montgomery County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Patrick County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince William County, VA, Pulaski County, VA, Rappahannock County, VA, Roanoke County, VA, Rockbridge County, VA, Rockingham County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA, Wythe County, VA, Berkeley County, WV, Grant County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Monroe County, WV, Morgan County, WV, Pendleton County, WV, Pocahontas County, WV, Tucker County, WV

The radar

The Sterling radar (KLWX), 126 km from the middle of the area, began a volume at 17:57 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, 5.9 hours before the alert went out and 132 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-pSkew-T log-p diagram, Washington/Dulle, VA at 12:00Z on 2015-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Washington/Dulle, VA at 12:00Z on 2015-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 166 square meters per square second.1939587897Sfc1 km3 km6 km9 kmRMLM
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.

IssuedProductOfficeCountiesLasted
Apr 20, 3:08 PM EDTTornado WatchSPCAllegany, Anne Arundel, Baltimore, Calvert, Caroline, Carroll and 13 more9 hr
Apr 20, 5:01 PM EDTMesoscale DiscussionSPCAllegany, Anne Arundel, Baltimore, Calvert, Carroll, Cecil and 12 more119 min
Apr 19, 9:06 PM EDTMesoscale DiscussionSPCBladen, Brunswick, Duplin, Durham, Edgecombe, Franklin and 13 more54 min
Apr 20, 2:25 AM EDTMesoscale DiscussionSPCBeaufort, Bertie, Camden, Chowan, Craven, Currituck and 16 more95 min
Apr 20, 1:03 PM EDTMesoscale DiscussionSPCAlexander, Anson, Buncombe, Burke, Cabarrus, Caldwell and 20 more57 min
Apr 20, 1:23 PM EDTTornado WatchSPCAlexander, Avery, Buncombe, Burke, Cabarrus, Caldwell and 20 more7 hr
Apr 20, 2:55 PM EDTSevere Thunderstorm WatchSPCAlamance, Alleghany, Anson, Ashe, Bertie, Caswell and 33 more7 hr
Apr 20, 4:18 PM EDTMesoscale DiscussionSPCAlexander, Buncombe, Burke, Cabarrus, Caldwell, Catawba and 12 more57 min
Apr 20, 6:27 PM EDTMesoscale DiscussionSPCAlamance, Alleghany, Caswell, Chatham, Durham, Forsyth and 16 more93 min
Apr 20, 6:45 PM EDTMesoscale DiscussionSPCAlexander, Anson, Avery, Buncombe, Burke, Caldwell and 15 more60 min
Apr 20, 3:23 PM EDTMesoscale DiscussionSPCBradford, Cameron, Centre, Clearfield, Clinton, Elk and 8 more2 hr
Apr 20, 5:57 PM EDTMesoscale DiscussionSPCBradford, Cameron, Centre, Clinton, Columbia, Luzerne and 9 more2 hr
Apr 20, 7:31 PM EDTMesoscale DiscussionSPCLackawanna, Susquehanna, Wayne2 hr
Apr 20, 7:56 PM EDTSevere Thunderstorm WatchSPCBradford, Carbon, Lackawanna, Luzerne, Monroe, Northampton and 4 more4 hr

Nearby

Mesoscale Discussions in Virginia, 2015Mesoscale Discussions in Maryland, 2015Mesoscale Discussions in West Virginia, 2015Every 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.