Alert archive / Virginia / Tornado Watches in 2011
Tornado Watch 251
The Storm Prediction Center issued this tornado watch at Apr 28, 2011, 7:38 AM EDT for 16 counties in Maryland; 89 counties in Virginia. It was in force for 7 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 28, 2011, 7:38 AM EDT (11:38 UTC)
- Expired
- Apr 28, 2011, 3:00 PM EDT
- In force
- 7 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 105 counties
Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Dorchester County, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Somerset County, MD, Wicomico County, MD, Worcester County, MD, Accomack County, VA, Albemarle County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Bedford County, VA, Brunswick County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Chesapeake, VA, City of Colonial Heights, VA, City of Danville, VA, City of Emporia, VA, City of Fairfax, VA, City of Falls Church, VA, City of Franklin, VA, City of Fredericksburg, VA, City of Hampton, VA, City of Hopewell, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Martinsville, VA, City of Newport News, VA, City of Norfolk, VA, City of Petersburg, VA, City of Poquoson, VA, City of Portsmouth, VA, City of Richmond, VA, City of Suffolk, VA, City of Virginia Beach, VA, City of Williamsburg, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Franklin County, VA, Gloucester County, VA, Goochland County, VA, Greene County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Henry County, VA, Isle of Wight County, VA, James City County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Lancaster County, VA, Loudoun County, VA, Louisa County, VA, Lunenburg County, VA, Madison County, VA, Mathews County, VA, Mecklenburg County, VA, Middlesex County, VA, Nelson County, VA, New Kent County, VA, Northampton County, VA, Northumberland County, VA, Nottoway County, VA, Orange County, VA, Patrick County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Southampton County, VA, Spotsylvania County, VA, Stafford County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA
The radar
The Sterling radar (KLWX), 63 km from the middle of the area, began a volume at 11:38 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
- 40%
- One or more EF2 to EF5 tornadoes
- 20%
- Ten or more severe wind reports
- 30%
- One or more gusts of 65 knots or more
- 30%
- Ten or more severe hail reports
- 10%
- One or more hailstones of 2 inches or more
- 5%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
22 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 28, 7:55 AM EDT | Tornado Warning | LWX | Baltimore, Carroll, Frederick | 27 min |
| Apr 28, 8:01 AM EDT | Flash Flood Warning | LWX | Frederick, Washington | 119 min |
| Apr 28, 8:12 AM EDT | Tornado Warning | LWX | Carroll, Frederick | 33 min |
| Apr 28, 8:14 AM EDT | Tornado Warning | LWX | Baltimore, Harford | 11 min |
| Apr 28, 8:45 AM EDT | Tornado Warning | LWX | Baltimore, Carroll | 30 min |
| Apr 28, 9:14 AM EDT | Tornado Warning | LWX | Baltimore, Carroll, Frederick, Howard, Montgomery | 31 min |
| Apr 28, 9:35 AM EDT | Severe Thunderstorm Warning | AKQ | Amelia, Caroline, Cumberland, Fluvanna, Goochland, Hanover and 3 more | 40 min |
| Apr 28, 9:39 AM EDT | Severe Thunderstorm Warning | LWX | Howard, Montgomery | 36 min |
| Apr 28, 9:45 AM EDT | Flash Flood Warning | LWX | Montgomery | 101 min |
| Apr 28, 9:49 AM EDT | Tornado Warning | LWX | Baltimore, Harford | 26 min |
| Apr 28, 10:03 AM EDT | Severe Thunderstorm Warning | LWX | King George, Spotsylvania, Stafford, City of Fredericksburg | 42 min |
| Apr 28, 10:09 AM EDT | Tornado Warning | AKQ | Goochland, Hanover, Henrico, Louisa, Powhatan | 36 min |
| Apr 28, 10:12 AM EDT | Severe Thunderstorm Warning | AKQ | Caroline, Essex, Hanover, Louisa, Richmond, Westmoreland | 48 min |
| Apr 28, 10:25 AM EDT | Tornado Warning | AKQ | Caroline, Essex, Hanover, King and Queen, Westmoreland | 35 min |
| Apr 28, 10:36 AM EDT | Flash Flood Warning | LWX | Baltimore, Carroll, Harford | 102 min |
| Apr 28, 10:38 AM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Calvert, Charles, Prince George's, Saint Mary's | 52 min |
| Apr 28, 10:54 AM EDT | Severe Thunderstorm Warning | LWX | Calvert, Charles, Saint Mary's | 66 min |
| Apr 28, 10:56 AM EDT | Severe Thunderstorm Warning | AKQ | Dorchester | 49 min |
| Apr 28, 11:09 AM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Calvert, Prince George's | 36 min |
| Apr 28, 11:22 AM EDT | Tornado Warning | LWX | Anne Arundel | 14 min |
| Apr 28, 11:26 AM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Calvert, Charles, Prince George's, Saint Mary's | 18 min |
| Apr 28, 11:46 AM EDT | Severe Thunderstorm Warning | AKQ | Dorchester, Wicomico | 26 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 00:00Z, 11.6 hours before the alert went out and 62 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
- 1143 J/kg
- Mixed-layer CIN
- -34 J/kg
- Mixed-layer LCL
- 834 m above ground
- 0-6 km bulk shear
- 47 kt
- 0-1 km storm-relative helicity
- 283 m²/s²
- 0-3 km storm-relative helicity
- 353 m²/s²
- Significant tornado parameter
- 1.8
- Supercell composite
- 14.0
The text
As transmitted, in the capitals the NWS used until 2016.
973
WWUS20 KWNS 281137
SEL1
SPC WW 281137
DCZ000-MDZ000-NCZ000-VAZ000-CWZ000-281900-
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 251
NWS STORM PREDICTION CENTER NORMAN OK
740 AM EDT THU APR 28 2011
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
DISTRICT OF COLUMBIA
MUCH OF MARYLAND
A SMALL PART OF NORTHWEST AND NORTHEAST NORTH CAROLINA
MUCH OF CENTRAL AND EASTERN VIRGINIA
COASTAL WATERS
EFFECTIVE THIS THURSDAY MORNING AND AFTERNOON FROM 740 AM UNTIL
300 PM EDT.
TORNADOES...HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE
MILES EAST AND WEST OF A LINE FROM 35 MILES NORTH NORTHEAST OF
BALTIMORE MARYLAND TO 35 MILES EAST OF DANVILLE VIRGINIA. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU1).
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.
OTHER WATCH INFORMATION...THIS TORNADO WATCH REPLACES TORNADO
WATCH NUMBER 247. WATCH NUMBER 247 WILL NOT BE IN EFFECT AFTER
740 AM EDT. CONTINUE...WW 249...WW 250...
DISCUSSION...A BROKEN BAND OF CONVECTION CONTINUES TO DEVELOP E OF
THE BLUE RIDGE AND THE SYNOPTIC COLD FRONT. A BREAK IN THE
CONVECTION IN NC IS ALLOWING AN UNIMPEDED INFLUX OF LOW-LEVEL
MOISTURE INTO VA...AND VERTICAL SHEAR PROFILES REMAIN STRONG. GIVEN
THE STRONG SHEAR AND MOIST PROFILES WITH WEAK INSTABILITY...THE
POTENTIAL FOR A FEW TORNADOES AND DAMAGING WINDS WITH
SUPERCELLS/BOWS WILL CONTINUE THROUGH AT LEAST MIDDAY OR EARLY
AFTERNOON.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
500. MEAN STORM MOTION VECTOR 22045.
...THOMPSONSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 27, 8:15 PM EDT | Severe Thunderstorm Watch | SPC | Kent, New Castle, Sussex | 8 hr |
| Apr 28, 4:05 AM EDT | Severe Thunderstorm Watch | SPC | Kent, New Castle, Sussex | 6 hr |
| Apr 28, 6:21 AM EDT | Mesoscale Discussion | SPC | Kent, New Castle | 54 min |
| Apr 28, 9:45 AM EDT | Severe Thunderstorm Watch | SPC | Kent, New Castle, Sussex | 6 hr |
| Apr 28, 10:44 AM EDT | Mesoscale Discussion | SPC | Kent, New Castle | 61 min |
| Apr 28, 11:49 AM EDT | Mesoscale Discussion | SPC | Kent, New Castle | 56 min |
| Apr 28, 2:00 PM EDT | Mesoscale Discussion | SPC | Kent, Sussex | 60 min |
| Apr 28, 12:27 AM EDT | Mesoscale Discussion | SPC | Allegany, Frederick, Howard, Montgomery, Washington | 63 min |
| Apr 28, 12:41 AM EDT | Tornado Watch | SPC | Allegany, Anne Arundel, Baltimore, Calvert, Carroll, Charles and 8 more | 7 hr |
| Apr 28, 2:41 PM EDT | Tornado Watch | SPC | Dorchester, Somerset, Wicomico, Worcester | 6 hr |
| Apr 28, 6:33 PM EDT | Mesoscale Discussion | SPC | Dorchester, Saint Mary's, Somerset, Wicomico, Worcester | 57 min |
| Apr 28, 3:32 AM EDT | Mesoscale Discussion | SPC | Hunterdon, Sussex, Warren | 28 min |
| Apr 27, 9:22 PM EDT | Mesoscale Discussion | SPC | Buchanan, Dickenson, Lee, Russell, Scott, Smyth and 5 more | 53 min |
| Apr 27, 10:12 PM EDT | Mesoscale Discussion | SPC | Albemarle, Alleghany, Amelia, Amherst, Appomattox, Arlington and 68 more | 63 min |
| Apr 28, 12:34 AM EDT | Mesoscale Discussion | SPC | Buchanan, Dickenson, Lee, Russell, Scott, Tazewell and 3 more | 26 min |
Nearby
Tornado Watches in Virginia, 2011Tornado Watches in Maryland, 2011Every tornado 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.