Alert archive / Pennsylvania / Severe Thunderstorm Watches in 2011
Severe Thunderstorm Watch 794
The Storm Prediction Center issued this severe thunderstorm watch at Aug 21, 2011, 12:52 PM EDT for 7 states. It was in force for 8 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 21, 2011, 12:52 PM EDT (16:52 UTC)
- Expired
- Aug 21, 2011, 9:00 PM EDT
- In force
- 8 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2 in
- Strongest gust expected
- 60 kt
All 125 counties
Kent County, DE, New Castle County, DE, Sussex County, DE, 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, Bergen County, NJ, Burlington County, NJ, Camden County, NJ, Cape May County, NJ, Cumberland County, NJ, Essex County, NJ, Gloucester County, NJ, Hudson County, NJ, Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Monmouth County, NJ, Morris County, NJ, Ocean County, NJ, Passaic County, NJ, Salem County, NJ, Somerset County, NJ, Sussex County, NJ, Union County, NJ, Warren County, NJ, Bronx County, NY, Kings County, NY, Nassau County, NY, New York County, NY, Orange County, NY, Putnam County, NY, Queens County, NY, Richmond County, NY, Rockland County, NY, Suffolk County, NY, Westchester County, NY, Adams County, PA, Bedford County, PA, Berks County, PA, Blair County, PA, Bucks County, PA, Cambria County, PA, Carbon County, PA, Centre County, PA, Chester County, PA, Clearfield 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, Somerset County, PA, Sullivan 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 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, 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, Jefferson County, WV
The radar
The Sterling radar (KLWX), 148 km from the middle of the area, began a volume at 16:54 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
- 80%
- One or more gusts of 65 knots or more
- 40%
- Ten or more severe hail reports
- 40%
- One or more hailstones of 2 inches or more
- 20%
- Six or more combined severe hail and wind reports
- 95%
Warnings issued inside it
51 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 21, 12:59 PM EDT | Severe Thunderstorm Warning | OKX | Putnam | 23 min |
| Aug 21, 1:09 PM EDT | Severe Thunderstorm Warning | OKX | Westchester | 21 min |
| Aug 21, 1:12 PM EDT | Severe Thunderstorm Warning | LWX | Fauquier, Loudoun, Prince William | 48 min |
| Aug 21, 1:14 PM EDT | Severe Thunderstorm Warning | LWX | Baltimore, Harford, City of Baltimore | 46 min |
| Aug 21, 1:24 PM EDT | Severe Thunderstorm Warning | LWX | Fauquier, Loudoun, Prince William | 51 min |
| Aug 21, 1:28 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Baltimore, Howard, Montgomery, Prince George's | 47 min |
| Aug 21, 1:29 PM EDT | Severe Thunderstorm Warning | LWX | Baltimore, City of Baltimore | 46 min |
| Aug 21, 1:39 PM EDT | Flash Flood Warning | LWX | Baltimore, City of Baltimore | 3 hr |
| Aug 21, 1:40 PM EDT | Severe Thunderstorm Warning | LWX | Frederick, Montgomery, Washington | 50 min |
| Aug 21, 1:43 PM EDT | Severe Thunderstorm Warning | OKX | Putnam, Rockland, Westchester | 47 min |
| Aug 21, 1:47 PM EDT | Severe Thunderstorm Warning | PHI | Burlington, Camden, Mercer | 58 min |
| Aug 21, 1:50 PM EDT | Severe Thunderstorm Warning | LWX | Fairfax, Fauquier, Loudoun, Prince William | 40 min |
| Aug 21, 1:54 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Baltimore, Harford, City of Baltimore | 51 min |
| Aug 21, 1:58 PM EDT | Severe Thunderstorm Warning | LWX | Fairfax, Fauquier, Prince William, City of Manassas | 47 min |
| Aug 21, 2:01 PM EDT | Tornado Warning | LWX | Anne Arundel | 29 min |
| Aug 21, 2:01 PM EDT | Severe Thunderstorm Warning | PHI | Cecil, Kent, Queen Anne's | 59 min |
| Aug 21, 2:01 PM EDT | Severe Thunderstorm Warning | CTP | Centre, Mifflin, Snyder, Union | 59 min |
| Aug 21, 2:05 PM EDT | Severe Thunderstorm Warning | LWX | Culpeper, Fauquier, Madison, Prince William, Rappahannock, City of Manassas and 1 more | 40 min |
| Aug 21, 2:15 PM EDT | Severe Thunderstorm Warning | OKX | Putnam | 21 min |
| Aug 21, 2:15 PM EDT | Tornado Warning | CTP | Centre, Mifflin, Snyder, Union | 21 min |
| Aug 21, 2:19 PM EDT | Tornado Warning | LWX | Baltimore | 26 min |
| Aug 21, 2:39 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel | 36 min |
| Aug 21, 2:43 PM EDT | Severe Thunderstorm Warning | PHI | Burlington, Camden, Gloucester, Mercer | 62 min |
| Aug 21, 2:50 PM EDT | Severe Thunderstorm Warning | LWX | Albemarle, City of Charlottesville | 21 min |
| Aug 21, 2:52 PM EDT | Severe Thunderstorm Warning | CTP | Juniata, Mifflin, Perry, Snyder | 53 min |
| Aug 21, 2:55 PM EDT | Severe Thunderstorm Warning | PHI | Kent, Queen Anne's, Talbot | 65 min |
| Aug 21, 3:08 PM EDT | Severe Thunderstorm Warning | PHI | Burlington, Mercer, Middlesex, Monmouth, Ocean | 67 min |
| Aug 21, 3:11 PM EDT | Severe Thunderstorm Warning | LWX | Montgomery, Prince George's | 49 min |
| Aug 21, 3:12 PM EDT | Severe Thunderstorm Warning | LWX | Montgomery, Prince George's | 48 min |
| Aug 21, 3:21 PM EDT | Severe Thunderstorm Warning | PHI | Monmouth, Ocean | 54 min |
| Aug 21, 3:28 PM EDT | Severe Thunderstorm Warning | CTP | Cumberland, Dauphin, Juniata, Lancaster, Lebanon, Northumberland and 4 more | 62 min |
| Aug 21, 3:31 PM EDT | Flash Flood Warning | PHI | Philadelphia | 8 hr |
| Aug 21, 3:46 PM EDT | Flash Flood Warning | PHI | Burlington | 2 hr |
| Aug 21, 4:00 PM EDT | Severe Thunderstorm Warning | OKX | Putnam, Westchester | 45 min |
| Aug 21, 4:06 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Calvert, Prince George's | 39 min |
| Aug 21, 4:07 PM EDT | Severe Thunderstorm Warning | OKX | Kings, Nassau, Queens | 38 min |
| Aug 21, 4:14 PM EDT | Severe Thunderstorm Warning | PHI | Monmouth, Ocean | 46 min |
| Aug 21, 4:29 PM EDT | Severe Thunderstorm Warning | CTP | Dauphin, Lancaster, Lebanon | 44 min |
| Aug 21, 4:37 PM EDT | Tornado Warning | OKX | Putnam, Westchester | 38 min |
| Aug 21, 4:45 PM EDT | Flash Flood Warning | PHI | Kent | 3 hr |
| Aug 21, 4:47 PM EDT | Severe Thunderstorm Warning | OKX | Nassau, Queens, Suffolk | 17 min |
| Aug 21, 4:48 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Calvert, Prince George's | 27 min |
| Aug 21, 4:58 PM EDT | Tornado Warning | OKX | Putnam | 30 min |
| Aug 21, 5:09 PM EDT | Severe Thunderstorm Warning | PHI | Caroline, Kent, Queen Anne's, Talbot | 37 min |
| Aug 21, 6:05 PM EDT | Flash Flood Warning | PHI | Burlington | 6 hr |
| Aug 21, 6:12 PM EDT | Severe Thunderstorm Warning | PHI | Burlington, Mercer, Middlesex, Monmouth, Ocean | 63 min |
| Aug 21, 6:46 PM EDT | Flash Flood Warning | OKX | Bergen, Passaic | 56 min |
| Aug 21, 7:03 PM EDT | Severe Thunderstorm Warning | PHI | Kent, Sussex | 42 min |
| Aug 21, 7:18 PM EDT | Severe Thunderstorm Warning | PHI | Monmouth, Ocean | 42 min |
| Aug 21, 7:24 PM EDT | Flash Flood Warning | PHI | Mercer, Monmouth, Ocean | 5 hr |
| Aug 21, 8:18 PM EDT | Flash Flood Warning | OKX | Kings, Nassau, Queens | 97 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, 4.9 hours before the alert went out and 146 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.
- Mixed-layer CAPE
- 1589 J/kg
- Mixed-layer CIN
- -99 J/kg
- Mixed-layer LCL
- 969 m above ground
- 0-6 km bulk shear
- 37 kt
- 0-1 km storm-relative helicity
- 131 m²/s²
- 0-3 km storm-relative helicity
- 125 m²/s²
- Significant tornado parameter
- 0.6
- Supercell composite
- 4.9
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 21, 11:54 AM EDT | Mesoscale Discussion | SPC | Kent, New Castle, Sussex | 2 hr |
| Aug 21, 7:12 PM EDT | Mesoscale Discussion | SPC | Kent, New Castle, Sussex | 63 min |
| Aug 21, 2:06 PM EDT | Severe Thunderstorm Watch | SPC | Dorchester, Somerset, Wicomico, Worcester | 7 hr |
| Aug 21, 6:42 PM EDT | Mesoscale Discussion | SPC | Somerset | 63 min |
| Aug 21, 1:20 PM EDT | Severe Thunderstorm Watch | SPC | Albany, Broome, Chenango, Columbia, Cortland, Delaware and 19 more | 8 hr |
| Aug 21, 4:34 PM EDT | Mesoscale Discussion | SPC | Albany, Clinton, Columbia, Delaware, Essex, Franklin and 12 more | 116 min |
| Aug 21, 1:45 PM EDT | Mesoscale Discussion | SPC | Amelia, Appomattox, Brunswick, Buckingham, Campbell, Charlotte and 22 more | 90 min |
| Aug 21, 1:43 PM EDT | Mesoscale Discussion | SPC | Calhoun, Doddridge, Gilmer, Jackson, Mason, Pleasants and 4 more | 62 min |
Nearby
Severe Thunderstorm Watches in Pennsylvania, 2011Severe Thunderstorm Watches in Virginia, 2011Severe Thunderstorm Watches in New Jersey, 2011Every severe thunderstorm watch in 2011
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.