Alert archive / Virginia / Tornado Watches in 2004

Tornado Watch 815

September 8, 20044 states

The Storm Prediction Center issued this tornado watch at Sep 8, 2004, 6:40 PM EDT for 4 states. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued
Sep 8, 2004, 6:40 PM EDT (22:40 UTC)
Expired
Sep 9, 2004, 12:00 AM EDT
In force
5 hr
Issued by
the Storm Prediction Center
All 80 counties

Allegany County, MD, Anne Arundel County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Washington County, MD, Adams County, PA, Bedford County, PA, Cumberland County, PA, Franklin County, PA, Fulton County, PA, Somerset County, PA, Amelia County, VA, Arlington County, VA, Caroline County, VA, Charles City County, VA, Chesterfield County, VA, City of Alexandria, VA, City of Colonial Heights, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Hopewell, VA, City of Manassas, VA, City of Manassas Park, VA, City of Petersburg, VA, City of Poquoson, VA, City of Richmond, VA, City of Williamsburg, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Cumberland County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Frederick County, VA, Gloucester County, VA, Goochland County, VA, Greene County, VA, Hanover County, VA, Henrico 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, Madison County, VA, Mathews County, VA, Middlesex County, VA, New Kent County, VA, Northumberland County, VA, Nottoway County, VA, Orange County, VA, Page County, VA, Powhatan County, VA, Prince George County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Surry County, VA, Warren County, VA, Westmoreland County, VA, York County, VA, Berkeley County, WV, Hampshire County, WV, Jefferson County, WV, Morgan County, WV

The radar

The Sterling radar (KLWX), 9 km from the middle of the area, began a volume at 22:41 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.

Warnings issued inside it

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

IssuedProductOfficeCountiesLasted
Sep 8, 6:40 PM EDTSevere Thunderstorm WarningLWXHampshire65 min
Sep 8, 6:57 PM EDTFlash Flood WarningCTPSomerset6 hr
Sep 8, 7:08 PM EDTTornado WarningAKQHanover, Henrico37 min
Sep 8, 7:33 PM EDTFlash Flood WarningLWXHampshire3 hr
Sep 8, 7:42 PM EDTTornado WarningAKQChesterfield33 min
Sep 8, 7:44 PM EDTSevere Thunderstorm WarningLWXFrederick, City of Winchester46 min
Sep 8, 8:08 PM EDTFlash Flood WarningLWXFrederick3 hr
Sep 8, 8:09 PM EDTTornado WarningAKQHanover, Henrico, City of Richmond36 min
Sep 8, 8:11 PM EDTTornado WarningAKQHanover, Henrico, City of Richmond34 min
Sep 8, 8:32 PM EDTFlash Flood WarningLWXPage, Shenandoah3 hr
Sep 8, 8:46 PM EDTFlash Flood WarningLWXWashington4 hr
Sep 8, 9:36 PM EDTFlash Flood WarningLWXAllegany3 hr
Sep 8, 11:53 PM EDTFlash Flood WarningLWXFrederick, City of Winchester2 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

Washington/Dulle, VA (KIAD), launched 12:00Z, 10.7 hours before the alert went out and 1 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-pSkew-T log-p diagram, Washington/Dulle, VA at 12:00Z on 2004-09-08Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 188 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Washington/Dulle, VA at 12:00Z on 2004-09-08The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 57 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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
188 J/kg
Mixed-layer CIN
-3 J/kg
Mixed-layer LCL
490 m above ground
0-6 km bulk shear
31 kt
0-1 km storm-relative helicity
57 m²/s²
0-3 km storm-relative helicity
106 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

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

000 
WWUS20 KWNS 082307
SEL5  
SPC WW 082205
DCZ000-MDZ000-PAZ000-VAZ000-WVZ000-CWZ000-090400-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 815...CORRECTED
NWS STORM PREDICTION CENTER NORMAN OK
605 PM EDT WED SEP 8 2004

...CORRECTED FOR WATCH REPLACEMENT NUMBER...

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

       DISTRICT OF COLUMBIA
       WESTERN AND CENTRAL MARYLAND
       SOUTH CENTRAL PENNSYLVANIA
       CENTRAL AND NORTHERN VIRGINIA
       THE EASTERN WEST VIRGINIA PANHANDLE
       COASTAL WATERS

EFFECTIVE THIS WEDNESDAY NIGHT FROM 605 PM UNTIL MIDNIGHT EDT.

TORNADOES...HAIL TO 0.5 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS
TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE TORNADO WATCH AREA IS ALONG AND 60 STATUTE MILES EAST AND WEST
OF A LINE FROM 35 MILES NORTH NORTHWEST OF HAGERSTOWN MARYLAND TO
30 MILES SOUTH SOUTHEAST OF RICHMOND VIRGINIA.

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 814. WATCH NUMBER 814 WILL NOT BE IN EFFECT AFTER 605
PM EDT. 

DISCUSSION...THREAT FOR LOW LEVEL ROTATION EXPECTED TO PERSIST FOR
SEVERAL MORE HOURS IN TSTMS DEVELOPING IN SERN QUADRANT OF REMNANTS
OF FRANCES.  EXPECT GREATEST POTENTIAL TO REMAIN FOCUSED OVER
CNTRL VA NNW INTO N CNTRL VA/THE ERN WV PANHANDLE AND W CNTRL
MD...WHERE COMBINATION OF LOW LEVEL DIRECTIONAL SHEAR...CONVERGENCE
AND INSTABILITY WILL BE MAXIMIZED. THREAT SHOULD DIMINISH AS
BOUNDARY LAYER SLOWLY COOLS LATER IN THE EVENING.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE WIND
GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500.
MEAN STORM MOTION VECTOR 19025.


...CORFIDI

400,0765 370,0760 370,0781 400,0790

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 8, 12:00 PM EDTMesoscale DiscussionSPCCharles2 hr
Sep 8, 12:50 PM EDTTornado WatchSPCCharles, Prince George's6 hr
Sep 8, 3:39 PM EDTMesoscale DiscussionSPCAnne Arundel, Baltimore, Calvert, Charles, Howard, Montgomery and 3 more2 hr
Sep 8, 6:50 AM EDTTornado WatchSPCBland, Brunswick, Campbell, Carroll, Charlotte, Dinwiddie and 18 more7 hr
Sep 8, 8:41 AM EDTMesoscale DiscussionSPCBrunswick, Campbell, Carroll, Charlotte, Dinwiddie, Floyd and 17 more2 hr

Nearby

Tornado Watches in Virginia, 2004Tornado Watches in Maryland, 2004Tornado Watches in Pennsylvania, 2004Every tornado watch in 2004

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.