Alert archive / Virginia / Tornado Watches in 2011

Tornado Watch 811

August 27, 20114 states

The Storm Prediction Center issued this tornado watch at Aug 27, 2011, 10:41 AM EDT for 4 states. It was in force for 9 hr.

The area

The outline as issued.

The facts

Issued: Aug 27, 2011, 10:41 AM EDT (14:41 UTC)
Expired: Aug 27, 2011, 8:05 PM EDT
In force: 9 hr
Issued by: the Storm Prediction Center
Strongest gust expected: 65 kt

All 52 counties

Kent County, DE, New Castle County, DE, Sussex County, DE, Calvert County, MD, Caroline County, MD, Dorchester County, MD, Kent County, MD, Queen Anne's County, MD, Saint Mary's County, MD, Somerset County, MD, Talbot County, MD, Wicomico County, MD, Worcester County, MD, Atlantic County, NJ, Burlington County, NJ, Cape May County, NJ, Cumberland County, NJ, Middlesex County, NJ, Monmouth County, NJ, Ocean County, NJ, Salem County, NJ, Accomack County, VA, Charles City County, VA, City of Chesapeake, VA, City of Franklin, VA, City of Hampton, VA, City of Hopewell, VA, City of Newport News, VA, City of Norfolk, VA, City of Portsmouth, VA, City of Suffolk, VA, City of Virginia Beach, VA, City of Williamsburg, VA, Essex County, VA, Gloucester County, VA, Isle of Wight County, VA, James City County, VA, King and Queen County, VA, King William County, VA, Lancaster County, VA, Mathews County, VA, Middlesex County, VA, New Kent County, VA, Northampton County, VA, Northumberland County, VA, Prince George County, VA, Richmond County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA

The radar

The Dover AFB radar (KDOX), 124 km from the middle of the area, began a volume at 14:41 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: 30%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 10%
One or more gusts of 65 knots or more: 20%
Ten or more severe hail reports: 5%
One or more hailstones of 2 inches or more: 5%
Six or more combined severe hail and wind reports: 30%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Aug 27, 10:44 AM EDT	Tornado Warning	AKQ	City of Chesapeake, City of Norfolk, City of Portsmouth, City of Virginia Beach	31 min
Aug 27, 12:12 PM EDT	Tornado Warning	PHI	Sussex	28 min
Aug 27, 12:50 PM EDT	Flash Flood Warning	LWX	Calvert, Saint Mary's	6 hr
Aug 27, 5:09 PM EDT	Flash Flood Warning	LWX	Anne Arundel, Calvert, Charles, Prince George's, Saint Mary's	9 hr
Aug 27, 6:22 PM EDT	Tornado Warning	PHI	Kent, Sussex	23 min
Aug 27, 7:27 PM EDT	Flash Flood Warning	PHI	Kent, Sussex	12 hr

Discussions around it

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

The nearest sounding before it

Wallops Is Stn, VA (KWAL), launched 12:00Z, 2.7 hours before the alert went out and 53 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: 330 J/kg
Mixed-layer CIN: -8 J/kg
Mixed-layer LCL: 691 m above ground
0-6 km bulk shear: 35 kt
0-1 km storm-relative helicity: 105 m²/s²
0-3 km storm-relative helicity: 221 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.9

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

224 
WWUS20 KWNS 271443
SEL1
SPC WW 271443
DEZ000-MDZ000-NJZ000-VAZ000-CWZ000-280000-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 811
NWS STORM PREDICTION CENTER NORMAN OK
1040 AM EDT SAT AUG 27 2011

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

       DELAWARE
       EASTERN MARYLAND
       SOUTHERN NEW JERSEY
       SOUTHEAST VIRGINIA
       COASTAL WATERS

EFFECTIVE THIS SATURDAY MORNING AND EVENING FROM 1040 AM UNTIL
800 PM EDT.

TORNADOES...THUNDERSTORM WIND GUSTS TO 75 MPH...AND DANGEROUS
LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 45 STATUTE
MILES EAST AND WEST OF A LINE FROM 35 MILES SOUTHWEST OF NORFOLK
VIRGINIA TO 15 MILES NORTH OF ATLANTIC CITY NEW JERSEY.  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...CONTINUE...WW 810...

DISCUSSION...SEVERAL CONVECTIVE BANDS TO THE NORTH OF THE CENTER OF
HURRICANE IRENE CONTINUE TO CONTAIN SMALL ROTATING CELLS.  THESE ARE
MOVING ONSHORE INTO THE TIDEWATER NEAR VIRGINIA BEACH AND EAST OF
CHESAPEAKE BAY OVER COASTAL VA AND MD.  A THREAT FOR A FEW TORNADOES
WILL GRADUALLY SHIFT NWD ALONG THE COAST AS IRENE MOVES NNEWD PER
LATEST NHC FORECAST.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH EXTREME
TURBULENCE AND SURFACE WIND GUSTS TO 65 KNOTS. A FEW CUMULONIMBI
WITH MAXIMUM TOPS TO 400. MEAN STORM MOTION VECTOR 11040.


...WEISS

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 27, 7:52 AM EDT	Mesoscale Discussion	SPC	Sussex	113 min
Aug 27, 10:31 AM EDT	Mesoscale Discussion	SPC	Sussex	29 min
Aug 27, 1:01 PM EDT	Mesoscale Discussion	SPC	Kent, New Castle, Sussex	119 min
Aug 27, 4:44 PM EDT	Mesoscale Discussion	SPC	Sussex	2 hr
Aug 27, 7:31 PM EDT	Mesoscale Discussion	SPC	New Castle	89 min
Aug 27, 7:56 PM EDT	Tornado Watch	SPC	Kent, New Castle, Sussex	9 hr
Aug 27, 12:32 AM EDT	Tornado Watch	SPC	Somerset, Wicomico, Worcester	10 hr
Aug 27, 3:06 AM EDT	Mesoscale Discussion	SPC	Somerset, Wicomico, Worcester	114 min
Aug 26, 11:06 PM EDT	Mesoscale Discussion	SPC	Brunswick, Charles City, Chesterfield, Dinwiddie, Gloucester, Greensville and 30 more	84 min

Nearby

Tornado Watches in Virginia, 2011 Tornado Watches in Maryland, 2011 Tornado Watches in New Jersey, 2011 Every 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.