Alert archive / Virginia / Tornado Watches in 2009

Tornado Watch 239

May 4, 200955 counties in Virginia

The Storm Prediction Center issued this tornado watch at May 4, 2009, 12:29 PM EDT for 55 counties in Virginia. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: May 4, 2009, 12:29 PM EDT (16:29 UTC)
Expired: May 4, 2009, 5:15 PM EDT
In force: 5 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

All 55 counties

Accomack County, VA, Amelia County, VA, Appomattox County, VA, Bedford County, VA, Brunswick County, VA, Campbell County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Chesapeake, VA, City of Colonial Heights, VA, City of Danville, VA, City of Emporia, VA, City of Franklin, VA, City of Hampton, VA, City of Hopewell, 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 Roanoke, VA, City of Salem, VA, City of Suffolk, VA, City of Virginia Beach, VA, City of Williamsburg, VA, Cumberland County, VA, Dinwiddie County, VA, Franklin County, VA, Gloucester County, VA, Greensville County, VA, Halifax County, VA, Henrico County, VA, Henry County, VA, Isle of Wight County, VA, James City County, VA, King and Queen County, VA, Lunenburg County, VA, Mathews County, VA, Mecklenburg County, VA, New Kent County, VA, Northampton County, VA, Nottoway County, VA, Patrick County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Roanoke County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 118 km from the middle of the area, began a volume at 16:32 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: 20%
Ten or more severe wind reports: 20%
One or more gusts of 65 knots or more: 20%
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: 60%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
May 4, 1:49 PM EDT	Severe Thunderstorm Warning	AKQ	City of Chesapeake, City of Norfolk, City of Portsmouth, City of Virginia Beach	27 min
May 4, 1:57 PM EDT	Severe Thunderstorm Warning	AKQ	City of Chesapeake, City of Virginia Beach	33 min
May 4, 2:23 PM EDT	Severe Thunderstorm Warning	AKQ	Northampton	37 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

Roanoke, VA (KRNK), launched 12:00Z, 4.5 hours before the alert went out and 105 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: 45 J/kg
Mixed-layer CIN: -5 J/kg
Mixed-layer LCL: 540 m above ground
0-6 km bulk shear: 42 kt
0-1 km storm-relative helicity: 254 m²/s²
0-3 km storm-relative helicity: 220 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.4

Open this sounding in Storm Lab

The text

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

566 
WWUS20 KWNS 041628
SEL9  
SPC WW 041628
VAZ000-CWZ000-042200-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 239
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM EDT MON MAY 4 2009

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

       SOUTHERN AND SOUTHEAST VIRGINIA
       COASTAL WATERS

EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 1230 PM UNTIL
600 PM EDT.

TORNADOES...HAIL TO 2 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 130 STATUTE
MILES EAST AND WEST OF A LINE FROM 55 MILES NORTH OF SOUTH HILL
VIRGINIA TO 30 MILES EAST SOUTHEAST OF SOUTH HILL VIRGINIA.  FOR
A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU9).

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 238...

DISCUSSION...RAPID DESTABILIZATION HAS OCCURRED ALONG STRONG WARM
FRONT AND AHEAD OF VORT MAX CROSSING THE APPALACHIANS. EXPECT TSTMS
TO INCREASE FROM SOUTH OF THE BLUE RIDGE TO THE TIDEWATER THROUGH
THE AFTERNOON. STRONG EFFECTIVE SHEAR OF UP TO 50KT ACROSS THIS
REGION WILL SUPPORT SUPERCELLS WITH SOME TORNADIC POTENTIAL ALONG
THE WARM FRONT AND AHEAD OF SURFACE WAVE RIPPLING EAST ALONG THE
FRONT. STORMS CROSSING TO THE COOL SIDE OF THE BOUNDARY WILL EXIST
IN AN ENVIRONMENT WITH STEEP LAPSE RATES AND SUFFICIENT EFFECTIVE
SHEAR FOR HAIL PRODUCTION.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
450. MEAN STORM MOTION VECTOR 26030.


...CARBIN

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 4, 12:03 PM EDT	Mesoscale Discussion	SPC	Amelia, Brunswick, Charles City, Chesterfield, Dinwiddie, Gloucester and 33 more	57 min
May 4, 1:30 PM EDT	Severe Thunderstorm Watch	SPC	Isle of Wight, Southampton, City of Chesapeake, City of Franklin, City of Norfolk, City of Portsmouth and 2 more	9 hr
May 4, 3:26 PM EDT	Mesoscale Discussion	SPC	Charles City, Chesterfield, Gloucester, Henrico, James City, Mathews and 15 more	64 min

Nearby

Tornado Watches in Virginia, 2009 Every tornado watch in 2009

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.