Supercell Storm Results in Rare Significant Tornadoes
in Pulaski County, VA April 8th, 2011

On Friday evening April 8, 2011, several intense storms moved out of West Virginia and into southwest Virginia. Some of these storms were supercells, which contain very strong and rotating updrafts, capable of producing a full range of severe weather (damaging downburst winds, large hail, and sometimes tornadoes). One of these supercells tracked across a stationary frontal boundary, where shallow cool air had wedged down in from the northeast across much of Virginia, meeting warm, moist air pushing up from the southwest into far southwest Virginia. Supercells interacting with surface frontal boundaries can often be a recipe for tornadogenesis, and in fact that is what happened over Pulaski County. Two tornado tracks were identified in the aftermath of this torm, the first touched down in the southwest portion of the town of Pulaski at 7:33pm and resulted in high-end EF2 damage (winds up to 125 mph), and a second tornado tracked across Interstate 81 and through the community of Draper around 7:40pm, resulting in high-end EF1 damage (winds up to 110 mph). Fortunately, there were no fatalities during these tornadoes, however there were several minor injuries and many residents in both communities had their homes destroyed or suffered major damaged (over 50). There were a total of 267 structures with at least minor damage.

A text summary of the tornado tracks is at the bottom of this page.

The map below is an estimate of the damage paths of each tornado, and includes tags to a few photos taken by the National Weather Service storm survey team (click on the blue tag to see the photo). It is worth noting that any damage between what was determined to be the initial touchdown point of the second tornado near the National Guard Armory, and where it crossed Interstate 81 at Exit 92. is likely intermittent and mostly to trees. The damage then became more continuous as it crossed the interstate into Draper. The area across Draper Mountain was difficult to survey thoroughly.



You can view the Pulaski County tornado tracks in a larger map.

 

tor1 tor2

The above photos were taken by Dakota Burton on Madison Ave in Pulaski looking west. These are believed to be of the tornado. The left-hand image shows heavy rain wrapping around the west side of the tornado (behind it from this view). The right-hand image was take just a few seconds later and appears to be zoomed in somewhat.

 

THE FOLLOWING DISCUSSION AND IMAGES PROVIDE A BRIEF METEOROLOGICAL BAKGROUND OF THIS SIGNIFICANT TORNADIC STORM:

The long term climatology of the mountain-valley region west of the Blue Ridge, and specifically within the New River Valley area, shows that tornadoes are extremely rare in this area. In fact, since 1950, no tornadoes had ever been documented in Pulaski County. Furthermore, longer term historical records of significant tornadoes (F2 or greater) indicate that no strong tornadoes have ever occurred in Pulaski County, or in several other counties surrounding it. Tornadoes tend to be more common west of the Appalachians, including portions of far southwest Virginia, as well as east of the Blue Ridge escarpment.

climo

The map above shows all tornado tracks in the period from 1950-2010 (thus, does NOT show the Pulaski County tornadoes on April 8, 2011). There was an F0 in Radford in June 1998, but the closest F2 tornadoes have been in Carroll County (1977), Roanoke area (1953 and 1974), and a couple in southeast West Virginia. Most recently in Alleghany County NC, an EF2 occurred at about 3,000 ft in elevation around midnight on May 9 2009.

 

On April 8, 2011, the surface map seen below showed a frontal boundary draped across the Midwest states, with a weak low pressure near the Ohio River, with a warm front pushing up through West Virginia and far southwest Virginia, but transitioning to a back-door cool front with high pressure nosing down across the rest of Virginia from the northeast. Storms initially formed in the warm, unstable air south of the low in eastern Kentucky and West Virginia, and then moved east toward the frontal boundary.

fronts

vis

The visible satellite image above has both surface observations and an analysis of the frontal boundaries overlaid. The time of the image is 7:15pm, less than 20 minutes before the tornado touched down in Pulaski. The yellow arrow points to the overshooting top of the supercell storm as it approached Pulaski County from the northwest. The overshooting top is an indication of a very powerful updraft.

 

loop

The image above is a radar mosaic loop of the storms that moved through southwest Virginia the evening of April 8, 2011. The label "A" is the location of Pulaski, and the strongest supercell of the day moved directory over this location. The gray-shaded "spike" that briefly shows up from the radar location through Pulaski (and beyond) is actually a signature indicating sunset, which just happens to be in the same direction that Pulaski is from the radar, and happened to occur shortly after the storm passed through Pulaski. It is NOT any indication of the tornado.

Even though this loop ends soon after the storm leaves Pulaski County, it remained strong all the way to the North Carolina border, with a significant circulation detected by Doppler radar. However, to our knowledge, only isolated damage with otherwise lots of large hail was reported southeast of the tornadoes. This is likely due to the fact that the storm moved into cooler and more stable low level air on the east side of the boundary, making it more difficult for the strong downdraft of the storm to reach the ground. The image below shows the tracks of persistent rotational signatures measured by area radars from the storms that evening.

nssl

 

The following radar images show the radar precipitation field (or "reflectivity"), as well as Doppler velocity fields at roughly the time of each tornado touchdown. Captions below each image offer a little more description.

refl_2333 srm_2333

The radar image above on the left shows the reflectivity "hook echo" as the counter-clockwise circulation of the storm wraps around the location where the tornado was just forming, as it moved into the southest portion of Pulaski at 7:33pm. The image on the right (same time) shows the Doppler velocities, with red indicating winds blowing to the west and green blowing toward the east in this case. The yellow circle is drawn to indicate the larger rotation of the supercell updraft area ("mesocyclone"), and within this a tighter rotational signature likely indicating the tornadic scale circulation can be seen coincident with where the tornado damage first began. It is very rare for the radar to detect the actual tornadic signature unless the storm is fairly close to the radar and the tornado is fairly significant. Both were the case here. (These images are from GR2Analyst by Gibson Ridge Software)

 

refl_2342 srm_2342

The above images are similar to the ones just shown, but in this case about the time the second tornado crossed I-81 and into Draper (7:42pm). The hook echo is still evident on the left-hand reflectivity image, whereas the circulation signatures on the left-hand velocity image are a little more complicated. The parent mesocycle is indicated by the yellow circle overlaid, but the tornadic signature is somewhat separated from this orginal updraft area, and may represent a new updraft and what isknown as a "mesocyclone occlusion" taking place. This suggests a new tornado may have formed, which was on a slightly different path from the first one. (These images are from GR2Analyst by Gibson Ridge Software)

 

In summary, while the climatology of this particular region suggest tornadoes of any kind, let alone strong tornadoes, are extremely rare here, clearly if favorable conditions come together they can occur. The storms developed in an unstable environment to the west, and one in which very strong wind shear was also present through the atmosphere (not shown). Supercell storms have passed through the New River Valley before, but rarely producing tornadoes. In this case, the interaction with a low-level boundary between warm air to the southwest and cool air to the northeast likely played a significant role in the development of the tornado, as low-level shear along the boundary was tilted in the vertical by the updraft. In addition, the local terrain may have also played a role in the development or strength of the tornadoes, with stretching from the storms moving down slopes helping to increase the spin (like stretching a jump rope while swinging it between two people will make it swing faster). We hope to study these effects in greater depth over time.

The bottom line is that tornadoes can occur even where they may considered climatologically very rare...and may again some day. People need to be prepared to take appropriate actions to protect themselves and their families as soon as a warning is issued, or when they can observe a bad storm is arriving. Fortunately, most were able to do so on the evening of April 8, 2011. 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 survey for the Pulaski County tornadoes:

 

...MULTIPLE TORNADOES CONFIRMED ON APRIL 8 2011...

...TORNADO CONFIRMED NEAR PULASKI IN PULASKI COUNTY VIRGINIA...

LOCATION...PULASKI IN PULASKI COUNTY VIRGINIA
DATE...APRIL 8 2011
ESTIMATED TIME...733 PM EDT
MAXIMUM EF-SCALE RATING...EF2
ESTIMATED MAXIMUM WIND SPEED...125 MPH
MAXIMUM PATH WIDTH...400 YARDS
PATH LENGTH...1.95 MILES
BEGINNING LAT/LON...37.049N / 80.803W
ENDING LAT/LON...37.033N / 80.775W
* FATALITIES...0
* INJURIES...9

* 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 PULASKI IN PULASKI COUNTY VIRGINIA ON APRIL 8 2011.
INITIAL TOUCHDOWN OCCURRED ALONG THE MOUNT OLIVET ROAD. TORNADO
TRAVELED SOUTHEAST WITH THE MOST SIGNIFICANT DAMAGE ALONG PULASKI
STREET...VALLEY ROAD...AND MAPLE STREET. SEVERAL ROOFS WERE TORN OFF
OF HOMES...TOP FLOORS OR ATTICS OF A COUPLE HOMES WERE COMPLETELY
DESTROYED...A COUPLE OF HOMES WERE KNOCKED OFF THEIR FOUNDATIONS...A
VEHICLE WAS FLIPPED OVER ON ITS BACK...AND NUMEROUS LARGE TREES WERE
SNAPPED OFF. THE TORNADO LIFTED NEAR THE INTERCHANGE OF HIGHWAY 11
AND HERMOSA DRIVE.

THIS INFORMATION CAN ALSO BE FOUND ON OUR WEBSITE AT
WEATHER.GOV/RNK.

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.

&&

...TORNADO CONFIRMED NEAR DRAPER IN PULASKI COUNTY VIRGINIA

LOCATION...NEAR DRAPER IN PULASKI COUNTY VIRGINIA
DATE...APRIL 8 2011
ESTIMATED TIME...737 PM EDT
MAXIMUM EF-SCALE RATING...EF1
ESTIMATED MAXIMUM WIND SPEED...105-110 MPH
MAXIMUM PATH WIDTH...480 YARDS
PATH LENGTH...3.1 MILES
BEGINNING LAT/LON...37.028N / 80.774W
ENDING LAT/LON...36.995N / 80.735W
* FATALITIES...0
* INJURIES...1

* 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 DRAPER IN PULASKI COUNTY VIRGINIA ON APRIL 8 2011.

INITIAL TOUCHDOWN ON HIGHWAY 11 NEAR THE NATIONAL GUARD ARMORY.
TORNADO TRACKED SOUTHEAST WITH INTERMITTENT DAMAGE OVER TERRAIN AND
WOODED AREA THAT WAS DIFFICULT TO SURVEY...BEFORE MORE CONTINUOUS
DAMAGE WAS OBSERVED AS IT CROSSED INTERSTATE 81 AT DRAPER NEAR EXIT
92. THERE WAS SIGNIFICANT DAMAGE IN THIS AREA TO A GAS STATION AND
MANY HOMES. ONE MOBILE HOME WAS COMPLETELY DESTROYED. NUMEROUS TREES
WERE ALSO SNAPPED OFF. THE TORNADO EVENTUALLY LIFTED ABOUT A HALF
MILE SOUTHEAST OF OLD BALTIMORE ROAD AS IT MOVED UP A SMALL RIDGE.

THIS INFORMATION CAN ALSO BE FOUND ON OUR WEBSITE AT
WEATHER.GOV/RNK.

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.