Alert archive / Virginia / Mesoscale Discussions in 2008

Mesoscale Discussion 672

April 20, 20089 counties in Maryland; Cumberland County, Perry County, York County, Pennsylvania; 21 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2008, 6:44 PM EDT for 9 counties in Maryland; Cumberland County, Perry County, York County, Pennsylvania; 21 counties in Virginia. It was in force for 61 min.

The area

The outline as issued.

The facts

Issued: Apr 20, 2008, 6:44 PM EDT (22:44 UTC)
Expired: Apr 20, 2008, 7:45 PM EDT
In force: 61 min
Issued by: the Storm Prediction Center

All 33 counties

Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Harford County, MD, Howard County, MD, Kent County, MD, Cumberland County, PA, Perry County, PA, York County, PA, Caroline County, VA, Charles City County, VA, City of Colonial Heights, VA, City of Fredericksburg, VA, City of Hopewell, VA, City of Petersburg, VA, City of Richmond, VA, City of Williamsburg, VA, Essex County, VA, Hanover County, VA, Henrico County, VA, James City County, VA, King and Queen County, VA, King George County, VA, King William County, VA, New Kent County, VA, Prince George County, VA, Richmond County, VA, Stafford County, VA, Surry County, VA, Westmoreland County, VA

The radar

The Sterling radar (KLWX), 53 km from the middle of the area, began a volume at 22:46 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.

Tornado Watch 210Apr 20, 8:00 PM EDT

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 10.7 hours before the alert went out and 45 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: 497 J/kg
Mixed-layer CIN: -4 J/kg
Mixed-layer LCL: 530 m above ground
0-6 km bulk shear: 36 kt
0-1 km storm-relative helicity: 112 m²/s²
0-3 km storm-relative helicity: 154 m²/s²
Significant tornado parameter: 0.3
Supercell composite: 1.4

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 19, 9:00 PM EDT	Mesoscale Discussion	SPC	Alleghany, Amherst, Bath, Bedford, Botetourt, Campbell and 23 more	60 min
Apr 20, 11:20 AM EDT	Mesoscale Discussion	SPC	Chesterfield, Dinwiddie, Greensville, Hanover, City of Colonial Heights, City of Emporia and 3 more	2 hr
Apr 20, 1:14 PM EDT	Mesoscale Discussion	SPC	Amelia, Appomattox, Bedford, Brunswick, Campbell, Charlotte and 21 more	2 hr
Apr 20, 1:47 PM EDT	Severe Thunderstorm Watch	SPC	Brunswick, Caroline, Charles City, Charlotte, Chesterfield, Dinwiddie and 43 more	8 hr
Apr 20, 4:20 PM EDT	Mesoscale Discussion	SPC	Brunswick, Dinwiddie, Greensville, Halifax, Isle of Wight, Lunenburg and 19 more	85 min
Apr 20, 7:14 PM EDT	Mesoscale Discussion	SPC	Amelia, Brunswick, Caroline, Charles City, Charlotte, Chesterfield and 42 more	61 min

Nearby

Mesoscale Discussions in Virginia, 2008 Mesoscale Discussions in Maryland, 2008 Mesoscale Discussions in Pennsylvania, 2008 Every mesoscale discussion in 2008

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.