Alert archive / Virginia / Tornado Watches in 2011
Tornado Watch 866
The Storm Prediction Center issued this tornado watch at Oct 13, 2011, 4:28 PM EDT for 11 counties in Maryland; 31 counties in Virginia. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Oct 13, 2011, 4:28 PM EDT (20:28 UTC)
- Expired
- Oct 13, 2011, 8:02 PM EDT
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1 in
- Strongest gust expected
- 60 kt
All 42 counties
Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Charles County, MD, City of Baltimore, MD, Dorchester County, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Arlington County, VA, Caroline County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Manassas, VA, City of Manassas Park, VA, Culpeper County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Gloucester County, VA, Hanover County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Lancaster County, VA, Loudoun County, VA, Louisa County, VA, Mathews County, VA, Middlesex County, VA, New Kent County, VA, Northumberland County, VA, Orange County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Spotsylvania County, VA, Stafford County, VA, Westmoreland County, VA
The radar
The Sterling radar (KLWX), 72 km from the middle of the area, began a volume at 20:30 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
- 40%
- One or more hailstones of 2 inches or more
- 30%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
7 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Oct 13, 4:47 PM EDT | Tornado Warning | AKQ | Hanover, King William, New Kent | 28 min |
| Oct 13, 5:07 PM EDT | Tornado Warning | LWX | Fauquier, Prince William, City of Manassas | 23 min |
| Oct 13, 5:13 PM EDT | Tornado Warning | AKQ | Essex, King and Queen, King William | 31 min |
| Oct 13, 5:28 PM EDT | Tornado Warning | LWX | Fairfax, Prince William, Stafford | 32 min |
| Oct 13, 5:35 PM EDT | Tornado Warning | LWX | Fairfax, City of Fairfax | 25 min |
| Oct 13, 6:04 PM EDT | Tornado Warning | AKQ | Caroline, Hanover, Louisa | 26 min |
| Oct 13, 6:14 PM EDT | Tornado Warning | LWX | Spotsylvania | 31 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, 8.5 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.
- Mixed-layer CAPE
- 69 J/kg
- Mixed-layer CIN
- -167 J/kg
- Mixed-layer LCL
- 451 m above ground
- 0-6 km bulk shear
- 36 kt
- 0-1 km storm-relative helicity
- 115 m²/s²
- 0-3 km storm-relative helicity
- 180 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- -0.0
The text
As transmitted, in the capitals the NWS used until 2016.
255
WWUS20 KWNS 132029
SEL6
SPC WW 132029
DCZ000-MDZ000-VAZ000-CWZ000-140300-
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 866
NWS STORM PREDICTION CENTER NORMAN OK
430 PM EDT THU OCT 13 2011
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
DISTRICT OF COLUMBIA
SOUTHERN MARYLAND
EASTERN VIRGINIA
COASTAL WATERS
EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 430 PM UNTIL
1100 PM EDT.
TORNADOES...HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS
TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 50 STATUTE
MILES EAST AND WEST OF A LINE FROM 20 MILES NORTH OF WASHINGTON
DISTRICT OF COLUM TO 35 MILES EAST SOUTHEAST OF RICHMOND
VIRGINIA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).
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.
DISCUSSION...A SMALL CLUSTER OF SUPERCELLS HAS EVOLVED THIS
AFTERNOON INVOF OF A WARM/QUASI-STATIONARY BOUNDARY WHERE AIR MASS
IS MOIST AND MODERATELY UNSTABLE WITH MLCAPE OF AROUND 1000 J/KG.
THOUGH AMBIENT VERTICAL SHEAR IS NOT PARTICULARLY
STRONG...VERTICALLY VEERING WIND PROFILES COUPLED WITH THE MOIST/LOW
LCL BOUNDARY LAYER AND VORTICITY ENHANCEMENT ALONG THE SURFACE
BOUNDARY WILL ENHANCE LOW-LEVEL STORM ROTATION AND THE POTENTIAL FOR
A FEW TORNADOES.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND
GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500.
MEAN STORM MOTION VECTOR 20025.
...MEADSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Oct 13, 6:53 PM EDT | Mesoscale Discussion | SPC | Anne Arundel, Calvert, Charles, Dorchester, Howard, Montgomery and 3 more | 97 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.