Alert archive / Pennsylvania / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 636

September 8, 20126 states

The Storm Prediction Center issued this severe thunderstorm watch at Sep 8, 2012, 12:15 PM EDT for 6 states. It was in force for 9 hr.

The area

The outline as issued.

The facts

Issued: Sep 8, 2012, 12:15 PM EDT (16:15 UTC)
Expired: Sep 8, 2012, 8:56 PM EDT
In force: 9 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1 in
Strongest gust expected: 60 kt

All 114 counties

Kent County, DE, New Castle County, DE, Sussex County, DE, Allegany County, MD, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline 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, Atlantic County, NJ, Burlington County, NJ, Camden County, NJ, Cape May County, NJ, Cumberland County, NJ, Gloucester County, NJ, Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Monmouth County, NJ, Morris County, NJ, Ocean County, NJ, Salem County, NJ, Somerset County, NJ, Sussex County, NJ, Warren County, NJ, Adams County, PA, Bedford County, PA, Berks County, PA, Blair County, PA, Bucks County, PA, Carbon County, PA, Centre County, PA, Chester County, PA, Clinton County, PA, Columbia County, PA, Cumberland County, PA, Dauphin County, PA, Delaware County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Juniata County, PA, Lancaster County, PA, Lebanon County, PA, Lehigh County, PA, Lycoming County, PA, Mifflin County, PA, Monroe County, PA, Montgomery County, PA, Montour County, PA, Northampton County, PA, Northumberland County, PA, Perry County, PA, Philadelphia County, PA, Schuylkill County, PA, Snyder County, PA, Sullivan County, PA, Tioga County, PA, Union County, PA, York County, PA, 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 State College radar (KCCX), 126 km from the middle of the area, began a volume at 16:15 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: 20%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 95%
One or more gusts of 65 knots or more: 60%
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: 95%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Sep 8, 12:32 PM EDT	Severe Thunderstorm Warning	CTP	Cameron, Centre, Clearfield, Clinton, Lycoming, Potter and 1 more	58 min
Sep 8, 12:35 PM EDT	Severe Thunderstorm Warning	LWX	Frederick, Washington	40 min
Sep 8, 12:47 PM EDT	Tornado Warning	LWX	Washington	16 min
Sep 8, 12:55 PM EDT	Severe Thunderstorm Warning	CTP	Bedford, Blair, Centre, Cumberland, Franklin, Fulton and 6 more	65 min
Sep 8, 1:09 PM EDT	Severe Thunderstorm Warning	LWX	Carroll, Frederick, Washington	66 min
Sep 8, 1:09 PM EDT	Severe Thunderstorm Warning	CTP	Adams, Franklin, York	51 min
Sep 8, 1:29 PM EDT	Severe Thunderstorm Warning	CTP	Centre, Clinton, Huntingdon, Juniata, Lycoming, Mifflin and 5 more	61 min
Sep 8, 1:43 PM EDT	Severe Thunderstorm Warning	CTP	Adams, Cumberland, Dauphin, Franklin, Juniata, Northumberland and 3 more	62 min
Sep 8, 1:55 PM EDT	Severe Thunderstorm Warning	CTP	Dauphin, Lancaster, Lebanon, York	65 min
Sep 8, 2:10 PM EDT	Severe Thunderstorm Warning	LWX	Baltimore, Carroll, Frederick, Harford, Howard, Montgomery	80 min
Sep 8, 2:11 PM EDT	Severe Thunderstorm Warning	CTP	Columbia, Dauphin, Lebanon, Lycoming, Montour, Northumberland and 4 more	94 min
Sep 8, 2:16 PM EDT	Severe Thunderstorm Warning	LWX	Clarke, Frederick, Page, Rockingham, Shenandoah, Warren and 1 more	46 min
Sep 8, 2:28 PM EDT	Tornado Warning	LWX	Frederick, Shenandoah, Warren	20 min
Sep 8, 2:40 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Bucks, Chester, Lehigh, Montgomery, Northampton	65 min
Sep 8, 2:47 PM EDT	Severe Thunderstorm Warning	LWX	Montgomery	58 min
Sep 8, 2:52 PM EDT	Severe Thunderstorm Warning	PHI	Carbon, Monroe	53 min
Sep 8, 3:10 PM EDT	Severe Thunderstorm Warning	CTP	Lancaster, York	35 min
Sep 8, 3:16 PM EDT	Severe Thunderstorm Warning	LWX	Albemarle, City of Charlottesville	32 min
Sep 8, 3:22 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Charles, Howard, Montgomery, Prince George's	68 min
Sep 8, 3:29 PM EDT	Tornado Warning	LWX	Fairfax, City of Fairfax	20 min
Sep 8, 3:44 PM EDT	Tornado Warning	LWX	Arlington, Fairfax, City of Alexandria, City of Falls Church	15 min
Sep 8, 3:45 PM EDT	Severe Thunderstorm Warning	PHI	Hunterdon, Mercer, Morris, Sussex, Warren	60 min
Sep 8, 3:53 PM EDT	Tornado Warning	LWX	Montgomery, Prince George's	15 min
Sep 8, 3:58 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Baltimore, Calvert, Charles, Howard, Montgomery and 3 more	55 min
Sep 8, 4:06 PM EDT	Tornado Warning	LWX	Anne Arundel, Prince George's	39 min
Sep 8, 4:06 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Fauquier, Orange, Spotsylvania, Stafford, City of Fredericksburg	39 min
Sep 8, 4:29 PM EDT	Severe Thunderstorm Warning	PHI	Hunterdon, Mercer, Middlesex, Morris, Somerset, Sussex and 1 more	61 min
Sep 8, 4:30 PM EDT	Severe Thunderstorm Warning	PHI	Caroline, Kent, Queen Anne's, Talbot	60 min
Sep 8, 5:22 PM EDT	Severe Thunderstorm Warning	PHI	Kent, New Castle	53 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, 4.3 hours before the alert went out and 134 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: 252 J/kg
Mixed-layer CIN: -81 J/kg
Mixed-layer LCL: 638 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 150 m²/s²
0-3 km storm-relative helicity: 140 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 1.0

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 8, 2:12 PM EDT	Mesoscale Discussion	SPC	Kent, New Castle	93 min
Sep 8, 4:22 PM EDT	Mesoscale Discussion	SPC	Kent, New Castle, Sussex	53 min
Sep 8, 5:00 AM EDT	Mesoscale Discussion	SPC	Allegany, Garrett	60 min
Sep 8, 11:38 AM EDT	Mesoscale Discussion	SPC	Allegany, Baltimore, Carroll, Frederick, Howard, Montgomery and 2 more	97 min
Sep 8, 1:48 PM EDT	Severe Thunderstorm Watch	SPC	Dorchester, Somerset, Wicomico, Worcester	7 hr
Sep 8, 3:25 PM EDT	Mesoscale Discussion	SPC	Saint Mary's, Somerset	65 min
Sep 8, 10:39 AM EDT	Mesoscale Discussion	SPC	Bergen, Hudson, Passaic	2 hr
Sep 8, 11:18 AM EDT	Tornado Watch	SPC	Bergen, Essex, Hudson, Passaic, Union	10 hr
Sep 8, 1:30 PM EDT	Mesoscale Discussion	SPC	Bergen, Hudson	60 min
Sep 8, 12:57 AM EDT	Mesoscale Discussion	SPC	Chautauqua	2 hr
Sep 8, 8:42 AM EDT	Mesoscale Discussion	SPC	Broome, Cayuga, Chemung, Chenango, Cortland, Herkimer and 13 more	93 min
Sep 8, 10:03 AM EDT	Severe Thunderstorm Watch	SPC	Allegany, Cattaraugus, Cayuga, Chemung, Franklin, Genesee and 16 more	5 hr
Sep 8, 12:40 PM EDT	Tornado Watch	SPC	Albany, Broome, Chenango, Clinton, Columbia, Cortland and 22 more	7 hr
Sep 8, 2:46 PM EDT	Mesoscale Discussion	SPC	Albany, Clinton, Columbia, Delaware, Dutchess, Essex and 14 more	59 min
Sep 8, 3:55 PM EDT	Mesoscale Discussion	SPC	Columbia, Rensselaer, Washington	65 min
Sep 8, 6:17 PM EDT	Mesoscale Discussion	SPC	Suffolk	58 min
Sep 8, 12:20 PM EDT	Mesoscale Discussion	SPC	Amherst, Appomattox, Bedford, Botetourt, Buckingham, Campbell and 22 more	115 min
Sep 8, 7:10 PM EDT	Mesoscale Discussion	SPC	Greensville, Isle of Wight, Prince George, Southampton, Surry, Sussex and 3 more	65 min

Nearby

Severe Thunderstorm Watches in Pennsylvania, 2012 Severe Thunderstorm Watches in Virginia, 2012 Severe Thunderstorm Watches in Maryland, 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.