Alert archive / Virginia / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 484

July 9, 20129 counties in North Carolina; 32 counties in Virginia; Mercer County, West Virginia

The Storm Prediction Center issued this severe thunderstorm watch at Jul 9, 2012, 3:19 PM EDT for 9 counties in North Carolina; 32 counties in Virginia; Mercer County, West Virginia. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Jul 9, 2012, 3:19 PM EDT (19:19 UTC)
Expired: Jul 9, 2012, 7:46 PM EDT
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

All 42 counties

Alleghany County, NC, Ashe County, NC, Caswell County, NC, Rockingham County, NC, Stokes County, NC, Surry County, NC, Watauga County, NC, Wilkes County, NC, Yadkin County, NC, Amherst County, VA, Appomattox County, VA, Bedford County, VA, Bland County, VA, Botetourt County, VA, Buckingham County, VA, Campbell County, VA, Carroll County, VA, Charlotte County, VA, City of Danville, VA, City of Galax, VA, City of Lynchburg, VA, City of Martinsville, VA, City of Radford, VA, City of Roanoke, VA, City of Salem, VA, Craig County, VA, Floyd County, VA, Franklin County, VA, Giles County, VA, Grayson County, VA, Halifax County, VA, Henry County, VA, Montgomery County, VA, Nelson County, VA, Patrick County, VA, Pittsylvania County, VA, Pulaski County, VA, Roanoke County, VA, Smyth County, VA, Tazewell County, VA, Wythe County, VA, Mercer County, WV

The radar

The Roanoke radar (KFCX), 26 km from the middle of the area, began a volume at 19:20 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: 10%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 30%
One or more gusts of 65 knots or more: 10%
Ten or more severe hail reports: 20%
One or more hailstones of 2 inches or more: 5%
Six or more combined severe hail and wind reports: 60%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Jul 9, 4:13 PM EDT	Severe Thunderstorm Warning	RNK	Appomattox, Campbell, Charlotte	62 min
Jul 9, 6:29 PM EDT	Severe Thunderstorm Warning	RNK	Caswell	61 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, 7.3 hours before the alert went out and 49 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: 43 J/kg
Mixed-layer CIN: -217 J/kg
Mixed-layer LCL: 1063 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: -16 m²/s²
0-3 km storm-relative helicity: 68 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.

935 
WWUS20 KWNS 091925
SEL4
SPC WW 091925
MDZ000-NCZ000-VAZ000-WVZ000-100100-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 484
NWS STORM PREDICTION CENTER NORMAN OK
320 PM EDT MON JUL 9 2012

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

       MARYLAND
       NORTHWEST NORTH CAROLINA
       SOUTHWEST AND SOUTH CENTRAL VIRGINIA
       EXTREME SOUTHEAST WEST VIRGINIA

EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 320 PM UNTIL 900
PM EDT.

HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 70
STATUTE MILES EAST AND WEST OF A LINE FROM 35 MILES NORTH
NORTHWEST OF LYNCHBURG VIRGINIA TO 60 MILES WEST SOUTHWEST OF
DANVILLE VIRGINIA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU4).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION...CONTINUE...WW 483...

DISCUSSION...STORMS ARE EXPECTED TO INCREASE OVER SWRN VA THIS
AFTERNOON WITHIN A MODERATELY UNSTABLE ENVIRONMENT WITH MLCAPE OF
1500-2000 J/KG.  WESTERLY MID LEVEL WINDS OF 20-30 KTS WILL PROMOTE
ORGANIZED MULTICELL STORMS AND SHORT LINE SEGMENTS...WITH POTENTIAL
TO PRODUCE PRIMARILY DAMAGING WIND GUSTS.

AVIATION...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 27020.


...WEISS

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 9, 1:01 PM EDT	Mesoscale Discussion	SPC	Alexander, Avery, Buncombe, Burke, Caldwell, Catawba and 20 more	89 min
Jul 9, 1:36 PM EDT	Mesoscale Discussion	SPC	Alamance, Beaufort, Bertie, Caswell, Chatham, Chowan and 35 more	54 min
Jul 9, 2:59 PM EDT	Severe Thunderstorm Watch	SPC	Alamance, Beaufort, Bertie, Bladen, Camden, Carteret and 45 more	7 hr
Jul 9, 4:48 PM EDT	Mesoscale Discussion	SPC	Anson, Beaufort, Bertie, Bladen, Camden, Chowan and 39 more	87 min
Jul 9, 5:53 PM EDT	Mesoscale Discussion	SPC	Alamance, Alleghany, Caswell, Davie, Forsyth, Guilford and 7 more	97 min
Jul 9, 7:17 PM EDT	Mesoscale Discussion	SPC	Alamance, Beaufort, Bertie, Brunswick, Camden, Carteret and 25 more	88 min
Jul 9, 12:09 AM EDT	Mesoscale Discussion	SPC	Arlington, Caroline, Clarke, Culpeper, Fairfax, Fauquier and 21 more	96 min

Nearby

Severe Thunderstorm Watches in Virginia, 2012 Severe Thunderstorm Watches in North Carolina, 2012 Severe Thunderstorm Watches in West Virginia, 2012 Every severe thunderstorm watch in 2012

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.