Alert archive / Virginia / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 316

May 29, 201210 counties in Maryland; 33 counties in Virginia; 8 counties in West Virginia

The Storm Prediction Center issued this severe thunderstorm watch at May 29, 2012, 4:33 PM EDT for 10 counties in Maryland; 33 counties in Virginia; 8 counties in West Virginia. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: May 29, 2012, 4:33 PM EDT (20:33 UTC)
Expired: May 29, 2012, 9:02 PM EDT
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

All 51 counties

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, 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 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, Highland County, VA, King George County, VA, Loudoun 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), 58 km from the middle of the area, began a volume at 20:33 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.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 10%
One or more EF2 to EF5 tornadoes: 2%
Ten or more severe wind reports: 40%
One or more gusts of 65 knots or more: 10%
Ten or more severe hail reports: 30%
One or more hailstones of 2 inches or more: 5%
Six or more combined severe hail and wind reports: 60%

Warnings issued inside it

10 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
May 29, 4:34 PM EDT	Severe Thunderstorm Warning	LWX	Hampshire, Mineral, Morgan	41 min
May 29, 4:53 PM EDT	Severe Thunderstorm Warning	LWX	Washington	52 min
May 29, 4:59 PM EDT	Flash Flood Warning	LWX	Rockingham, Shenandoah	86 min
May 29, 5:01 PM EDT	Severe Thunderstorm Warning	LWX	Allegany, Washington	44 min
May 29, 5:26 PM EDT	Severe Thunderstorm Warning	LWX	Frederick, Washington	49 min
May 29, 5:45 PM EDT	Flash Flood Warning	LWX	Frederick, Washington	5 hr
May 29, 5:50 PM EDT	Severe Thunderstorm Warning	LWX	Frederick, Washington	40 min
May 29, 7:38 PM EDT	Flash Flood Warning	LWX	Montgomery	76 min
May 29, 8:10 PM EDT	Flash Flood Warning	LWX	Montgomery, Prince George's	96 min
May 29, 8:11 PM EDT	Flash Flood Warning	LWX	Arlington, Fairfax, City of Fairfax, City of Falls Church	76 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 8.6 hours before the alert went out and 66 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: 601 J/kg
Mixed-layer CIN: -150 J/kg
Mixed-layer LCL: 1156 m above ground
0-6 km bulk shear: 8 kt
0-1 km storm-relative helicity: -68 m²/s²
0-3 km storm-relative helicity: -33 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 29, 4:22 PM EDT	Mesoscale Discussion	SPC	Frederick, Washington	53 min
May 29, 7:48 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Charles, Kent, Prince George's	57 min
May 29, 9:48 AM EDT	Mesoscale Discussion	SPC	Brooke, Hancock	87 min
May 29, 10:27 AM EDT	Severe Thunderstorm Watch	SPC	Brooke, Hancock, Marion, Marshall, Monongalia, Ohio and 1 more	5 hr
May 29, 1:25 PM EDT	Mesoscale Discussion	SPC	Brooke, Hancock, Marshall, Ohio	65 min

Nearby

Severe Thunderstorm Watches in Virginia, 2012 Severe Thunderstorm Watches in Maryland, 2012 Severe Thunderstorm Watches in West Virginia, 2012 Every severe thunderstorm watch in 2012

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.