Three confirmed tornadoes in Blacksburg County Warning Area:
Part of historic tornado outbreak in Carolinas and Virginia
on April 16th, 2011

On Saturday April 16, 2011, parts of the mid-Atlantic region experienced one of the most significant outbreaks of violent tornadoes in many years. Central and eastern North Carolina were most seriously impacted with several deadly, long-track tornadoes (the count so far within the state of NC is 26 total tornadoes). The far southeast corner of the Blacksburg County Warning Area (CWA) experienced two of these tornadoes: one rated EF2 with a 26 mile path length beginning in Person County NC in the Raleigh CWA and ending in Halifax County VA, and another EF1 that began in Alamance County (Raleigh CWA) and moved into southern Caswell County NC, with a total path length of 11 miles (from the same storm, but a little earlier). A third tornado (EF0) occurred in Rockbridge County VA. The Rockbridge tornado (near Vesuvius) touched down just after 2pm and produced intermittent damage for a little over a mile, while the Alamance/Caswell tornado (crossing into Caswell near Jericho) occurred between 2:05 and 2:18, and then the long track Person-Halifax tornado lasted from 2:40 to 3:10pm, crossing into Halifax County just west of Virgilina. There were other tornadoes in southeastern Virginia during this outbreak (see map).

The storm system responsible for the tornadoes also produced significant flash flooding (mainly west of the Blue Ridge), as well as numerous straight line wind damage reports, both with thunderstorms ahead of the cold front and with strong westerly non-thunderstorm winds behind the front. This review will focus on the tornadoes however.

A text summary of the three tornado tracks in our area of responsibility can be found at the bottom of this page.

The three maps below show the damage paths of the tornadoes within the Blacksburg CWA (so NOT including the paths in Alamance and Person Counties), along with tags to a few photos taken during the damage surveys.


View Rockbridge County Tornado April 16, 2011 in a larger map

 


View Caswell County Tornado April 16, 2011 in a larger map

 


View Halifax County Tornado April 16th, 2011 in a larger map

 

THE FOLLOWING DISCUSSION AND IMAGES PROVIDE A BRIEF METEOROLOGICAL OVERVIEW OF THESE TORNADOES:

The tornado climatology of the region suggests tornadoes are relatively rare in the mountainous region compared to areas east of the Blue Ridge, and especially in the Piedmont where longer track and often more violent tornadoes have occurred many times in the past.

The map above shows all tornado tracks in the period from 1950-2010 (so does NOT show any tornadoes from the current spring season). The top area highlighted is over Rockbridge County, where only one tornado had ever been documented (June of 1975) prior to April 16, 2011. The lower area highlighted includes Pittsylvania and Halifax Counties in Virginia, and Caswell and Person Counties in North Carolina (Person is in the NWS Raleigh CWA), within which a number of tornado touchdowns and tracks have occurred since 1950. In fact, there have been three tornadoes very close to the state line near Virgilina since 1995 (two of them within the last 3 years), and as of April 16, 2011there has now been a fourth.

While Southwest Virginia and North-Central North Carolina can experience tornadoes in just about any month of the year, especially from early spring through late fall, the month of April is favored for especially strong tornadoes (EF2 or stronger). The graph below shows the months in which EF2 (F2 by the old Fujita scale) or stronger have occured in the 40 counties covered by the Blacksburg NWS between 1950 and 2009. Note that nothing stronger than an EF3 (or F3) has never been documented in our 40-county area. Close to half of all the tornadoes that occur in April in the Blacksburg CWA are EF2 or EF3. (For more details on the severe weather climatology of our region, please check out a Technical Memorandum published in 2006.)

 

On April 16, 2011, the 3pm surface map seen below (near the time of all three tornadoes) showed a vigorous cold front sweeping through the Appalachians, while a warm frontal boundary was sliding north up through southern Virginia. The airmass was fairly unstable east of the cold front and along and especially south of the warm front, while the atmospheric winds shear was extremely high ahead of the cold front and especially in the vicinity of the warm front.

 

The figures below show a vertical profile from the upper air balloon launch taken at noon from the Triad Airport near Greensboro (GSO), of temperature, moisture, and winds. On the left side, the sounding shows a modestly unstable airmass with strong southerly low level winds increasing and turning more southwest and west with height. On the upper right, the "hodograph" shows how the wind shear vectors are changing with height, and the large looping shape to this is a classic signature for strong supercell (often tornadic) storms. Many of the calculated parameters strongly suggest the possibility of tornadic supercells.

 

Because many important factors were coming together for a potential tornado outbreak, by noon the NOAA/NWS Storm Prediction Center in Norman, OK had forecast a "High" risk of severe weather (including strong tornadoes) for much of the eastern portion of North Carolina (a very rare thing for the them to do), and a "Moderate" risk of severe weather that included much of north central NC, and south-central and southeastern VA (see below).

 

Also around noon, the SPC had issued a Tornado Watch (below) for roughly the moderate risk area and a little west into Virginia. Included in this watch was mention of a "Particularly Dangerous Situation" (known as a "PDS Watch"), which they reserve for the most extreme conditions.

 

The loop below shows the radar evolution of the storm system on April 16 as it tracked across the Blue Ridge and into the Piedmont areas of Virginia and North Carolina, with imbedded storms in the broken line forming into supercells, which eventually became more isolated farther east and later in the afternoon. Label "A" shows the location of the Rockbridge County EF0 tornado, "B" shows where the Caswell County EF1 touched down, and line "C" shows the approximate track of the EF2 tornado in Person County NC and Halifax County VA. The red border shows the Blacksburg County Warning area, and orange lines are state borders.

The supercells that produced the three tornadoes in the Blacksburg CWA could be classified as "HP" (or High Precipitation) supercells. These are often identified less so by a classic "hook" echo on the southwest side, but more of a kidney bean appearance and sometimes evolving into a bow shape as they move toward the northeast.

 

The next several images and loops show close-up views of the storms about the time they produced tornadoes, with some important features pointed out. These images are all from "GR2Analyst" by Gibson Ridge Software.

On the left is the radar precipitation field (or "reflectivity"), and on the right is the Doppler velocity field at roughly the time of the Rockbridge tornado touchdown near Vesuvius (2:03pm). Captions below each image offer a little more description.

The storm, moving north-northeast through Rockbridge County, was actually stronger with a more significant circulation earlier, but as it began to collapse, that is when the tornado developed (as the storm came across a ridge line down into the South River Valley. The yellow circle on the right image shows the parent mesocyclone signature (location of the rotating updraft). The tornado itself could not be observed by the radar at this range (partly due to wide beam angle and also height above the ground), but a tornado warning had been issued about 20 minutes before this time, and included Vesuvius in the path.

 

The images below are similar, but show the reflectivity (left) and Doppler velocity (right) at about the time of the EF1 tornado in Caswell County near Jericho close to the border with Alamance County (2:13pm). In this case however, the closest NWS WSR-88D radar is from Raleigh (KRAX) instead of Floyd County (KFCX), so is what is shown. Captions below each image offer some further description.

The approximate location of the tornado is shown by the white "T" in the left image as it is about to cross from Alamance County into Caswell County. The tornado is apparently rain-wrapped, with high reflectivity values surrounding the tornadic circulation (seen on the right within the mesocyclone), but even in the higher reflectivity values a hint of a hook shape can be seen. The storm would be considered an "HP" supercell. Note there are other mesocyclone circulations (red outbound and green inbound winds near each other) associated with supercell storms to the north and to the south, but at this time they are not quite as strong.

 

This circulation with this same storm then weakened temporarily, before re-strengthened again as it moved through Person County. The animation below shows the evolution of the supercell in terms of the reflectivity, and look for the hook echo just north of Roxboro, even though it is embedded in an area of heavy rain (it would be nearly impossible to actual see the funnel).

 

Below is the animation of the Doppler velocity evolution. You should be able to see the tightening and strengthening of the circulation north of Roxboro, as it then moves into southern Halifax County west of Virgilina. It then weakens again east of Scottsburg as it crosses through the Staunton River State Park, which is where the EF2 tornado finally lifted after a total track of 26 miles.

 

While April is a climatologically favored month for tornadoes in our region, especially the stronger tornadoes (EF2 or greater), 2011 has been a particularly active April for tornadoes. The tornadoes of April 16 were part of an historic outbreak that impacted the Carolinas and Virginia with several long track and deadly tornadoes. Fortunately there were no deaths due to the tornadoes in the Blacksburg CWA, however there were 4 injuries in Halifax County, and there was one fatality when strong winds behind the front uprooted a tree in Wythe County Virginia (wet ground likely contributed to the tree being uprooted as well). Many homes and other structures were damaged, as well as large swaths of trees snapped or uprooted. Overall property damage was extensive, especially in Caswell and Halifax Counties. Tornado warnings werein effect for each of the three tornadoes in the Blacksburg CWA, with an average lead time of over 9 minutes.

Despite being favored from the spring months through the fall, tornadoes can occur at any time of the year within our region. When Hazardous Weather Outlooks include a heightened risk of severe weather, and/or when Tornado or Severe Thunderstorms Watches are issued as conditions become favorable, those are the times to prepare for appropriate courses of action should a tornado threaten your area. You need to remain alert for other weather alerts/warnings, and keep your eye to the sky. When a tornado warning is issued, it is best to take cover immediately, since this means a tornado has been observed on the ground or by radar, and is imminent for your location or very nearby.

Here is a link to some specific tornado and severe weather safety rules if you want to learn more!

 

Below is the summary of the National Weather Service Damage surveys for all three tornadoes, within the counties that is covered by the Blacksburg NWS:

    

 ...MULTIPLE TORNADOES CONFIRMED ON APRIL 16 2011...

============================================================

...TORNADO CONFIRMED NEAR JERICHO IN CASWELL COUNTY NORTH CAROLINA...

LOCATION...NEAR JERICHO IN CASWELL COUNTY NORTH CAROLINA
DATE...APRIL 16 2011
ESTIMATED TIME...2:13 PM EDT THROUGH 2:18 PM EDT
MAXIMUM EF-SCALE RATING...EF1
ESTIMATED MAXIMUM WIND SPEED...90 MPH
MAXIMUM PATH WIDTH...300 YARDS
PATH LENGTH...3.4 MILES
BEGINNING LAT/LON...36.24641N / 79.35650W
ENDING LAT/LON...36.27286N / -79.30490W
* FATALITIES...0
* INJURIES...0

* THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO
CHANGE PENDING FINAL REVIEW OF THE EVENT(S) AND PUBLICATION IN NWS
STORM DATA.

...SUMMARY...
THE NATIONAL WEATHER SERVICE IN BLACKSBURG VA HAS CONFIRMED A
TORNADO NEAR JERICHO IN CASWELL COUNTY NORTH CAROLINA ON APRIL
16 2011.

THE TORNADO CROSSED THE CASWELL/ALAMANCE COUNTY LINE SOUTH OF
JERICHO NORTH CAROLINA AT 2:13 PM EDT AS AN EFO TORNADO...
STRENGTHENING AS A EF1 TORNADO AS IT CROSSED VINSON ROAD.  
THE TORNADO THEN LIFTED AS AN EFO AS IT CROSSED HIGHWAY 119
NEAR BAYNES NORTH CAROLINA...WHICH IS ABOUT 4 MILES SOUTHEAST
OF JERICHO.  18 BARNS AND 1 SHED WAS DAMAGED.  10 HOMES WERE
DAMAGED... 7 WITH SEVERE DAMAGE AND 3 WITH MINOR DAMAGE. THERE
WERE NO REPORTED INJURIES.

MANY THANKS TO CASWELL COUNTY EMERGENCY MANAGEMENT OFFICIALS FOR
ASSISTANCE WITH THE SURVEY.


==========================================================

...TORNADO CONFIRMED FROM 4 MILES NORTHWEST OF VIRGILINA VIRGINIA
TO THE STAUNTON RIVER STATE PARK IN HALIFAX COUNTY VIRGINIA...

LOCATION...4 NW OF VIRGILINA IN HALIFAX COUNTY VIRGINIA
DATE...APRIL 16 2011
ESTIMATED TIME...250 PM EDT THROUGH 310 PM EDT
MAXIMUM EF-SCALE RATING...EF2
ESTIMATED MAXIMUM WIND SPEED...120 MPH
MAXIMUM PATH WIDTH...300 YARDS
PATH LENGTH...16.6 MILES
BEGINNING LAT/LON...36.542401N / -78.871354W
ENDING LAT/LON...36.720598N / -78.671165W
* FATALITIES...0
* INJURIES...4

* THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO
CHANGE PENDING FINAL REVIEW OF THE EVENT(S) AND PUBLICATION IN NWS
STORM DATA.

...SUMMARY...
THE NATIONAL WEATHER SERVICE IN BLACKSBURG VA HAS CONFIRMED A
TORNADO 4 MILES NORTHWEST OF VIRGILINA IN HALIFAX COUNTY VIRGINIA
ON APRIL 16 2011.

THIS TORNADO ORIGINALLY TOUCHED DOWN NEAR CONCORD IN IN PERSON
COUNTY NORTH CAROLINA AS AN EFO AT 240 PM EDT...STRENGTHENING AS
AN EF2 AS IT PASSED THROUGH BETHEL HILL NORTH CAROLINA...CROSSING
THE NORTH CAROLINA...VIRGINIA BORDER AROUND 250 PM. THIS TORNADO
REMAINED ON THE GROUND AS AN EF2...WITH INTERMITTENT EF1 DAMAGE...
ALL THE WAY TO THE STUANTON RIVER STATE PARK AT THE CONFLUENCE
OF THE DAN AND LOWER ROANOKE (STUANTON) RIVERS. 

THE ENTIRE PATH LENGTH OF THIS TORNADO WAS 26 MILES...16.6 MILES
OF WHICH WAS IN THE STATE OF VIRGINIA. THE TORNADO LIFTED PRIOR 
LEAVING THE STUANTON RIVER STATE PARK.  WITHIN HALIFAX COUNTY...
4 MOBILE HOMES WERE DESTROYED. 1 MOBILE HOME CONTAINED MAJOR
DAMAGE. 3 STICK BUILT HOMES HAD MAJOR DAMAGE. 4 HOMES HAD MINOR
DAMAGE...AND 4 HOMES WERE AFFECTED.  THERE WERE NUMEROUS 
OUTBUILDINGS AND SHEDS THAT WERE DAMAGED OR DESTROYED ALONG WITH
WIDESPREAD TREE DAMAGE WITHIN THE PATH OF THE TORNADO.  IT IS
ESTIMATED THAT 60 TO 100 ACRES OF TREES WERE DESTROYED WITHIN 
THE STAUNTON RIVER STATE PARK. 

MANY THANKS TO HALIFAX AND PERSON COUNTY EMERGENCY MANAGEMENT 
OFFICIALS FOR ASSISTANCE WITH THE SURVEY. 


=======================================================

...TORNADO CONFIRMED NEAR VESUVIUS IN ROCKBRIDGE COUNTY VIRGINIA...

LOCATION...VESUVIUS IN ROCKBRIDGE COUNTY VIRGINIA
DATE...APRIL 16 2011
ESTIMATED TIME...2:03 PM
MAXIMUM EF-SCALE RATING...EF0
ESTIMATED MAXIMUM WIND SPEED...85 MPH 
MAXIMUM PATH WIDTH...100
YARDS PATH LENGTH...1.3 MILES 
BEGINNING LAT/LON...37.901N / 79.202W 
ENDING LAT/LON...37.917N / 79.189W
* FATALITIES...0
* INJURIES...0

* THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO
CHANGE PENDING FINAL REVIEW OF THE EVENT(S) AND PUBLICATION IN NWS
STORM DATA.

...SUMMARY...
THE NATIONAL WEATHER SERVICE IN BLACKSBURG VA HAS CONFIRMED A
TORNADO NEAR VESUVIUS IN ROCKBRIDGE COUNTY VIRGINIA ON APRIL
16 2011.

THE TORNADO FIRST TOUCHED DOWN ALONG SOUTH RIVER ROAD AT 2:03 PM
LESS THAN A HALF MILE SOUTH OF THE INTERSECTION WITH HIGHWAY 56.
IT CROSSED SOUTH RIVER ROAD WITH MINOR DAMAGE TO A GARAGE...BARN...
AND HOUSE...AS WELL AS SNAPPING SEVERAL CEDAR TREES. THE BARN WAS
SLIGHTLY SHIFTED OFF ITS FOUNDATION. THE WIDTH OF THE DAMAGE PATH 
AT THIS POINT WAS ABOUT 100 YARDS WIDE. INTERMITTENT DAMAGE TO MAINLY
TREES...AS WELL AS SIDING TO SOME HOMES...CONTINUED NORTH-NORTHEAST 
BETWEEN SOUTH RIVER ROAD AND THE SOUTH RIVER...THEN CROSSED ROUTE 56
WITH VERY INTERMITTENT DAMAGE ALONG SOUTH BOTTOM ROAD TO NEAR THE 
AUGUSTA COUNTY BORDER. IN ONE LOCATION RIGHT IN VESUVIUS ALONG SOUTH
RIVER ROAD...A LARGE CEDAR TREE WAS UPROOTED AND FELL ON A METAL 
CARPORT. 

THE TOTAL LENGTH OF THE INTERMITTENT DAMAGE PATH WAS 1.3 MILES...WITH
MAXIMUM WINDS DETERMINED TO BE IN THE 75 TO 85 MILE RANGE. THIS PUTS 
THE TORNADO AT THE HIGH END OF THE EF0 RANGE. 


FOR REFERENCE...THE ENHANCED FUJITA SCALE CLASSIFIES TORNADOES INTO
THE FOLLOWING CATEGORIES:

EF0...WIND SPEEDS 65 TO 85 MPH.
EF1...WIND SPEEDS 86 TO 110 MPH.
EF2...WIND SPEEDS 111 TO 135 MPH.
EF3...WIND SPEEDS 136 TO 165 MPH.
EF4...WIND SPEEDS 166 TO 200 MPH.
EF5...WIND SPEEDS GREATER THAN 200 MPH.