6 AUGUST 1993 SOUTHEAST VIRGINIA TORNADO OUTBREAK:
THE PETERSBURG, VIRGINIA F4 TORNADO
Report written by
Barbara McNaught, Warning Coordination Meteorologist
at the NWS Baltimore-Washington Forecast Office
Laura Cook, Meteorologist-in-Charge
at the NWS Norfolk Weather Office
and Central Wills, Officer-in-Charge
at the NWS Richmond Weather Office
Tornadoes are not considered a common event in Virginia and many of the Commonwealth's people will tell you that they do not even consider tornadoes a threat. August 6, 1993 broke that myth and shocked many with the reality of destruction that tornadoes bring. Prior to 1993, Virginia averaged six tornadoes a year. Records kept since 1950 showed 263 total tornadoes reported in the state, 21 fatalities, and 192 injuries. There have been 56 fatalities since 1916. The most active year for tornadoes was 1975 with 22 and the most active day was October 13, 1983 with 10 tornadoes.
These statistics should help place in context the August 6, 1993 outbreak. Many records were broken. Eighteen tornadoes occurred on that day smashing the old record of ten. This brought the total for the year to 25 breaking the old record of 22 only eight months into the year. The Petersburg Tornado was rated an F-4 on the Fujita Damage Scale with estimated winds peaking near 210 mph. This is the strongest recorded tornado in Virginia since 1950. It was the costliest tornado with an estimated 47 million dollars in damages. The total estimated damage from the outbreak was 52.5 million dollars. Twenty-one Virginia jurisdictions were affected by tornado impacts.
This was not the deadliest tornado outbreak for Virginia. That occurred May 2, 1929 when five tornadoes killed 21 people and injured 70. In 1929, it was a relatively unpopulated state and there may have been more tornadoes that day that went unreported. By comparison, the August 6 tornadoes killed four and injured 259 people. The tornado that struck Petersburg injured as many people as all the tornadoes combined for the past 40 years in Virginia. While not the deadliest, it was the worst tornado as far as total citizens in the commonwealth affected. We can thank the rapid response of emergency services and medical personnel for saving lives and minimizing the potential death toll from this disaster.
After the Petersburg tornado, some people talked about how unusual it was for a tornado to strike that area of Virginia. While it was an unusual event, it was not a first. Petersburg was struck by an F-2 tornado on June 21, 1970 and an F-3 tornado on May 8, 1984. While no deaths or injuries occurred, there was significant damage. Nearby counties such as Chesterfield, Dinwiddie, Prince George, and Charles City have recorded nine, four, four, and five tornadoes respectively since 1950. Chesterfield has been one of the hotter tornado spots in Virginia's history.
Fujita Scale (F-scale) of Tornado Winds and Damage
|F #||Winds||Examples of Damage||# in Va||% Va|
|Light damage. Tree branches snapped; rotten trees down; TV antennas and signs damaged.||50||21|
|1||72-112||Moderate damage. Roofs peeled off; windows broken; trees snapped; trailers moved or overturned.||109||45|
|2||113-157||Considerable damage. Roofs torn off; weak structures and trailers demolished; trees uprooted; cars blown off road.||60||25|
|3||158-206||Severe damage. Roofs and some walls torn off well constructed houses; some rural buildings demolished; cars lifted and tumbled.||22||9|
|4||207-260||Devastating damage. Houses leveled leaving piles of debris; cars thrown some distance.||1||.5|
|5||261-318||Incredible damage. Well-built houses lifted clear off foundation and carried a considerable distance and disintegrated.||0||0|
Tornado 1 Lunenburg-Nottoway-Dinwiddie-Chesterfield
First touch down of the day occurred near the town of Kenbridge in Lunenburg County at 12:43 pm. Roofs were blown off a briquet plant and a furniture company. The tornado moved northeast into Nottoway County. Estimated damage to Luneburg County was 300,000 dollars. The tornado began as an F-0 on the Fujita damage scale with a path width 100 yards.
In Nottoway County the tornado strengthened to an F-1 were it leveled a barn, trees and some outbuildings on Route 46 near the west edge of Fort Pickett Military Reservation. A house along Route 46 also sustained some damage. Total damages in Nottoway County were estimated at 100,000 dollars. The tornado width was 100-150 yards.
The tornado crossed into Dinwiddie County on the Fort Pickett Military Reservation where it did minimal damage. The tornado crossed route 643 near the northeast corner of Fort Pickett and continued northeast across rural land to the town of Ford. By this point it had strengthened to an F-2. It struck a well-constructed house on route 622 in the town of Ford at 1:12 pm. The second level of the house was sheared off along with some of the wall. There were also windows gone on the first level. A 97 year old widow road out the storm in the first floor hallway closet. Near the house, a wooden shed, telephone poles, and large trees were leveled. The tornado tracked northeast to near the Chesterfield County line. It lifted near route 611 and 623. Average width was 150-175 yards. Total damage was 320,500 dollars.
About 5 miles to the northeast in Chesterfield County, the tornado again touched down with damage along Route 628, 634 and 692 for about 3.5 miles. The damage is rated F-0.
Total path length through the 4 counties was about 38 miles. Total damages are estimated at 720,500 dollars. Total life time of the tornado on the ground was about 40 minutes.
Tornado 2 Petersburg-Colonial Heights-Hopewell-Prince George
The most devastating tornado of the day touched down in the independent city of Petersburg at approximately 1:30 pm. This tornado rapidly grew in size and strength as it moved two miles northeast into the commercial historic district of Petersburg. Here, damage showed a path width of 300 yards. Much of this damage was of an F-2 magnitude, however, within this path were smaller paths (about 30 yards wide) of more concentrated F-4 damage (winds estimated near 210 mph). Because of this pattern, the tornado has been designated an F-4 multi-vortex tornado. The vortex of a large tornado can sometimes break down into smaller tornadoes which rotate around a central core. This is called a multi-vortex tornado.
Amazingly, no one was killed in Petersburg. Old Towne Petersburg had withstood Union troop barrages in 1864-65 during the Civil War. Most of the buildings date back to the mid 1800s. A fire in 1815 destroyed the original Old Towne which was established in the 17th century. The train station that was demolished was the oldest standing train station in Virginia. Fifty-eight buildings were badly damaged or destroyed.
The end unit of a row of three-story brick buildings was completely demolished so that all that remained was a portion of the first level back and side walls. This was a well-constructed building with the brick walls at least three bricks thick. In another row of two- and three-story attached buildings, a middle unit was demolished. This was also a three-story brick building. About three feet of the first level front wall remained and most of the first level back wall remained. The rest was gone along with the attached sidewalls of the adjacent units second and third levels. In the first floor was a restaurant. Thirty people were in this building, yet no one was killed.
About 100 feet or so to the right of the restaurant was the historic train station which was completely collapsed. This was a one or two story brick structure that had a large spanning roof making it more susceptible than the other units mentioned to being destroyed. A couple units to the left of the restaurant was a unit that had a solid brick wall with no windows. The wall was four bricks thick. A large hole about 2 to 3 feet in diameter had been punched through the wall. This was likely caused by an airborne missile generated by the tornado, perhaps a beam from the buildings roof. Behind this building was another row of buildings. A collapsed wall was observed to have been made of cinder blocks with steel reinforcement rods and a layer of bricks on the outside.
F-4 tornado winds were determined based on the construction, design and damage to the above mentioned buildings. Also of interest was a caboose located behind a building near the train station. The caboose had been anchored into ground and setting on a short piece on rail. The tornado moved the caboose about 20 feet off the track ripping the anchors from the ground. The caboose was moved in an opposite direction to the path of the tornado.
From Old Towne, the tornado moved across to the historic black neighborhood of Pocahontas Island at about 1:35 pm. Here it destroyed or heavily damaged 47 of the 57 homes on the island. Most of these homes were wood-framed houses. A 200 year old church was totally destroyed, however, a bible, open on a podium, was untouched. Damage was rated at an F-3 with a path width of 250 yards. Total damage to Petersburg and Pocahontas Island was estimated at 15 million dollars. Forty people were injured and over 100 buildings heavily damaged or destroyed, but there were no deaths.
From Pocahontas Island, the tornado crossed the river entering Colonial Heights and crossing Interstate 95 to the Southpark shopping area. Amazingly, no vehicles where struck on this normally very busy highway. Here, it went on to damage several large stores including a K-Mart, a waterbed store, a strip mall (Southgate Square) and then the Wal-Mart. Windows were blown out, some walls and roofs collapsed at the stores. Some remaining walls were splattered and pitted with debris. The tornado had narrowed to about 200 yards wide by this point (as described by eyewitnesses) and was weakening, but it still retained its multi-vortex characteristics when it struck the Wal-Mart.
The tornado was as wide as the Wal-Mart was long. It moved across the length of the store. A small vortex within the tornado struck the front of the store to the right of the main entrance area slicing a 20 yard wide path through the cinder-block wall and store roof. (This was from a vector direction of 230 degrees converging into the main path of the tornado). The vortex gives the storm a rating at the lower end of an F-3 with winds up to 175 mph. Damage outside the small vortex was F-2.
Three people were killed near the store front and another 198 injured. The deaths were to three women, 40, 48 and 56 years of age. In the parking lot between the Wal-Mart and Southgate Square, 500 cars were removed, all with windows blown out and many completely totaled having been tossed about and flipped over. Of the 185 people brought to area hospitals from Petersburg and Colonial Heights, only 23 had to be admitted. This is considered a typical percentage for disasters. Total damage in Colonial Heights was estimated at 29.5 million dollars.
Form the Wal-Mart, the tornado crossed the Appomattox River again, this time entering Prince George County. About a mile from the Wal-Mart at about 1:40 pm, it struck Tarmac Virginia, Inc., a sand and gravel pit company located on Puddledock Road. The second floor of the cinder block building collapsed. Several employees had sought cover there. One 28 year old man was crushed and killed between the cinder blocks and a large electrical panel that fell. Several cars and trucks were overturned. Large conveyor belts were twisted and overturned. One employee spotted the tornado and radioed a warning to others which likely saved some lives. Three employees evacuated a small shed just before it was totally destroyed.
The tornado path width was 125 yards. It was a strong F-2 with winds estimated near 150 mph. Damage at the Tarmac site was estimated at three-quarters of a million dollars. The remaining damage across Prince George County was primarily to trees.
The tornado crossed Interstate 295 damaging a tall brick barrier wall and headed for the independent city of Hopewell. Here it sliced through the northern section. Hardest hit was the Riverside Park Apartment Complex were it took off several roofs. The tornado caused minor damage to an additional 49 homes, major damage to 13 homes and destroyed two. It struck Hopewell around 1:45 pm. The tornado was rated an F-1 with a width of 75 to 100 yards. Damages were estimated at 2.2 million dollars. Eight people were injured.
The tornado weakened to an F-0 as it crossed Route 10 near the bridge and moved out over the confluence of the Appomattox and James Rivers. It dissipated before entering Charles City County. Total path length through three independent cities and one county was about 12 miles. Total damages were estimated at 47.5 million dollars. Total life time of the tornado on the ground was 15 to 20 minutes.
Tornado 3 Chesterfield-Henrico-New Kent
Within close proximity time- and distance-wise to the Petersburg tornado, another tornado touched down to the north in Chesterfield County. This tornado formed from the same storm that produced the Dinwiddie County tornado.
The tornado touched down and crossed Route 10 moving northeast into the Rivers Bend subdivision at about 1:40 pm. It produced widespread tree damage and only minor roof and window damage to the new well-constructed homes in the neighborhood. The tornado was rated an F-1 with a width of about 200 yards (most concentrated area of damage). The damage path to trees was actually about a half mile wide and it is estimated that the entire meso-cyclone (low pressure center of a thunderstorm complex) was on the ground. Strong inflow into the storm caused minor tree damage as wide as a mile across.
The tornado moved from Rivers Bend to strike the Virina-Enon Bridge on Interstate-295. The tornado sucked up water from the James River and was described as a rotating wall of water striking the bridge. It knocked over two tractor-trailer trucks on the bridge and flipped over two smaller trucks. Another tractor-trailer truck then collided with the first two. Five people were injured.
The tornado weakened to an F-0 as it moved northeast across Henrico County causing tree damage. The storm's path width had narrowed to 75 to 100 yards. It finally dissipated in New Kent County in the vicinity of Route 60 and 640. Total Path length was about 14 miles. No damage estimates were obtained for this tornado.
Tornado 4 - Charles City-New Kent
About 8 miles northeast of the Petersburg tornado track, another tornado touched down. This was likely produced by the same thunderstorm. Credible sources indicated material from the Wal-Mart could be found in the southwest portion of Charles City County (some 15 miles from the store). In Charles City County, along Route 650 and 609, tree damage begins. The time was estimated between 2:00 and 2:05 pm.
The tornado broadsided a mobile home rolling it on its side and destroying it. The home had been anchored at all four corners. The anchors were set three feet into the ground. The tornado continued across Cool Hill Road. Another anchored mobile home was rolled three times and completely demolished. The remaining damage to Charles City County was trees. Estimated damages were 115,000 dollars.
The tornado moved into New Kent County, crossed over highway 60 and dissipated. Damage to New Kent was to trees. Path width was 50 yards. The total path length was 6.5 miles. It was rated an F-1.
Tornado 5 - New Kent
Another tornado touched down in New Kent County. It was slightly to the right of the previous tornado and was, again, likely produced by the same storm. Damage began south of Interstate 64 and just west of Route 628. This was a wooded area. The tornado tracked north-northeast crossing I-64 at mile marker 217. The tornado track turned a little more to the northeast and then back to the north-northeast as it dissipated in the vicinity of Route 623 a little over a mile east of the New Kent County Court House. The total tornado path length was 4.75 miles. No dollar damage estimate.
Almost all of the damage in the county was to downed trees. Homes in the area did not sustain any wind damage. The path was largely inaccessible by foot and so most of the damage assessment was done by aerial survey by the county emergency services director. The initial touchdown width was 30 yards. At I-64 the tornado had widened to about 150 yards and F-1 intensity. The damage pattern was complicated by additional areas where tree damage widen to nearly half a mile. At first glance, it seemed this could be described by the storm also producing a micro burst. However, no other micro burst damage was found to have occurred from thunderstorms that day. Upon viewing pictures of the tree damage more closely, trees were not lain in a straight line pattern, but in a broader cyclonic pattern. Therefore, it is theorized that again the whole meso cyclone (rotating core of the thunderstorm complex) briefly touched down.
Tornado 6 - Southampton
At about 2:20 pm, a cooperative observer sighted a tornado about 4 miles west of Courtland. At that time it was seen throwing trees into his barn. Trees were uprooted and a shed was destroyed. The tornado moved over open fields with little else in its path to damage. The tornado was a F-0 to a low F-1 with a path length of about a mile. Estimated path width is 75 yards.
Tornado 7 - Sussex
At 2:27 pm a State Trooper sighted a tornado northwest of the town of Sussex. Trees were knocked down. At about 2:32 pm a tornado was sighted near the town of Waverly. The tornado crossed Route 40 just south of the town and moved east-northeast through a residential section. Most of the damage was to trees. Numerous pine trees were broken off at rooftop level. Some hardwoods were blown over with their roots exposed. A couple of houses had chimneys knocked off. One home had a small branch driven into its siding. All trees were blown to the left of the path of the storm indicating tornadic circulation. It crossed U.S. Route 460 and destroyed a peanut warehouse. The peanut warehouse was a metal building without much in the way of supports.
The tornado was classified as an F-1 when it moved through Waverly. The length of the damage path through Waverly was about 4 miles. The total path length from the State Trooper sighting through Waverly was 14 miles, but much of this area is remote and it is uncertain how much of the time the tornado was on the ground. The path width through Waverly was 100 yards. No damage estimates were obtained.
Tornado 8 - Surry
A tornado touched down near the intersection of Route 601 and 614 in the southwest part of the county. It was likely the same storm that struck Waverly. The tornado moved to the northeast across Route 615. The track was about 2.5 miles long and 150 yards wide. Numerous trees were broken off about 15 feet up. A chimney was knocked off a two-story house. Metal roofing was torn off a shed and outbuildings were damaged. Near Route 615, two houses and two cars were damaged and several trees uprooted. Tornado began as an F-0 and possibly reached the low end of an F-1 near Route 615.
Tornado 9 - Surry
The storm produced another tornado struck near the town of Surry. An apartment building on Route 626 west of Surry was damaged. The roof over three units was blown off and an in-wall was pulled away from the frame. A lot of siding was also pulled off. One car had its windows shattered. The tornado moved northeast causing moderate damage to trees along Route 641 just west of Route 31. Trees were also reported down near Scotland Wharf Ferry Terminal. The tornado was seen around 3:00 pm headed across the James River toward James City County.
The tornado was rated an F-1. The path length was about 5 miles. The path width averaged 100 yards. Damage estimates for Surry County (from both tornado 8 and 9) were 20,000 dollars.
Tornado 10 - James City-York
Fishermen spotted the tornado moving along the banks of the James River and onto land at approximately 2:50 pm. The tornado destroyed a recreation building owned by the employees on the BASF corporation grounds. Debris was scattered through the woods. A bathhouse was completely gone. Pine trees were snapped off.
The tornado moved into a trailer park at Blow Flats Road. Five mobile homes were rolled over. It continued into Innovative Marine Products where a storage trailer was thrown into a large metal manufacturing building which was flattened. It then moved across U.S. Highway 60 taking down many trees which blocked the interstate for hours. The tornado was rated at the high end of an F-1.
The tornado moved into York County and onto the southern section of the Naval Weapons Station entering a housing area. Many trees were down damaging the recreation center and a corner of a housing unit. Here the tornado was rated an F-0. HAM radio reported through the SKYWARN Network that a funnel spotted near the Naval Station and Yorktown at 3:07 pm.
Total tornado path length was about 7 to 8 miles. Path width narrowed from 150 yards as the tornado came off the river to 75 yards near the end of its trail. Damages to James City County were about 750,000 dollars. No dollar estimate of damages were provided by the Naval Weapons Station.
Tornado 11 - Isle of Wight
At about 3:00 pm, a tornado was sighted at the Franklin Airport. This is open area and no damages were reported to county officials or the National Weather Service (NWS). About 5 miles northeast of the airport, a man reported observing rotation within the thunderstorm but he did not see a funnel.
Tornado 12 - Newport News-Hampton
At 3:10 pm, a man on the James River Bridge reported seeing three funnel clouds over the river. He said two dissipated and the other became a tornado moving into the woods on the Newport News side of the river. The tornado moved northeast across Villa Road and through a Flea Market on Jefferson Avenue. Extensive damage occurred to expensive homes along Villa Road. Most damage was from trees falling onto homes. The Flea Market was a poorly constructed metal building. The tornado blew off the roof and some of the side walls. Pieces of metal could be seen wrapped around tree tops to the left of the buildings and for several blocks downwind.
The tornado moved northeast into the City of Hampton. Damage was slightly less. A portable classroom at Big Bethel High School was overturned and paneling was stripped off the end. Several air conditioners were torn off the top of a grocery store near the intersection of Hampton Roads Center Parkway and Interstate 64.
The tornado was classified an F-1. The tornado path length was approximately 12 miles. The tornado's width was 400 yards as it came off the river and it gradually narrowed to 100 yards as it moved through Hampton. Newport News reported 163 homes damaged, 12 condemned and damage costs at approximately 1.2 million. Approximately 85 homes were damaged in Hampton, 8 condemned and damage costs were 700,000 dollars. Eight people were injured in Newport News and two in Hampton. There were no fatalities.
The tornado moved onto Langley Air Force Base (AFB) mainly moving across open area and runways. Damage occurred to several F-15s parked at the end of a runway for an air show planned for the next day. There was also damage to a storage area. Langley AFB weather observations reported tornado sightings on two separate occasions at least an hour apart. The damaging tornado described was observed for approximately 20 minutes. A second tornado path was not found, but may have occurred over water or rural land or may have been a funnel that did not touch down.
Tornado 13 - Middlesex
At around 3:00 pm a tornado moved through an area near Stormont. Trees were snapped off near the landfill. A barn was damaged along Route 629 and a travel trailer was blown over. The tornado moved across Route 673 between Christ Church School and Locust Hill. Estimated damage in Middlesex was 34,000 dollars. The tornado was rated an F-0 with a path length of about 3 miles and a with of 100 yards.
Tornado 14 - Lancaster
At 3:15 pm, a tornado moved into White Stone from the Rappahonnock River down Beach Road for about a mile. Residents saw the swirling debris. Trees were broken off and homes were damaged from the fallen trees. Estimated damage was 55,000 dollars and the tornado was classified an F-0. The width of the damage path was 100 yards and it was on the ground for at least a mile. The tornado was from the same storm that hit Middlesex County and it may have been the same tornado.
Several vehicles were blown off the road into the ditch near Ottoman but there was no other damage reported in that area nor tornadoes sighted. It was therefore credited to strong thunderstorm winds. Ottoman is located to the north of both this path and that of the Middlesex tornado.
Tornado 15 - Northampton
At 3:50 pm, a tornado was sighted by several park personnel from Kiptopeke State Park. The tornado moved through trees breaking them off at about 15 feet up for about 100+ yards then moved over a cliff and tracked another 700 yards making a path about half a mile long. A second funnel was sighted over the water.
At least 105 trees were damaged or destroyed. Picnic tables were thrown. A 20 foot ornamental boat was thrown 120 feet. A construction trailer and another trailer were overturned. Damages ranged to 30,000 dollars. Park officials had received NWS warnings at 3:30 pm of the tornado threat and warned campers. Tornado was rated at the low end of an F-1. Path width was 150 yards. This tornado likely resulted from the same storm that struck Newport News, Hampton and Langley AFB.
Tornado 16 - Suffolk
At approximately 3:30 pm, residents hear a tornado and saw trash and debris swirling up in their yards. Four homes were damaged. Several trees were knocked down. Two homes under construction were knocked off their foundation by several feet. Most of the area that the tornado passed over was open land. This storm was rated the low end of an F-1 with a path length of 2 miles with a width of 75 yards.
Tornado 17 - Chesapeake
Around 4:00 pm, a tornado moved through the Great Bridge area of Cheasa-peake. It first struck along Hanbury Road near Great Bridge High School just west of Route 168 and moved east through Etheridge Manor and Etheridge Woods neighbor-hoods. Many residents were not at home. Those that were heard a sound like a freight train; a few thought they saw the funnel cloud. At least 35 homes were damaged.
The area east of Route 168 appeared to have sustained the most damage. A brick two-car garage was flattened, several roofs were at least partially gone and numerous houses had the attic portion of the walls on the windward side of their house blown out. Most of the remaining damage along the path was due to trees being broken off and falling on houses. All downed trees and the garage were blown to the left of the direction of the path of the tornado. Most of the trees in this area were pine and were broken off near the rooftop level.
The tornado was classified an F-2 and caused an estimated 1.8 million dollars in damage. No injuries or deaths occurred. The path length was 2.5 miles and its width was 200 yards.
Tornado 18 - Virginia Beach
This tornado was produced by the same storm that produced the Chesapeake tornado. A tornado/waterspout was sighted moving east across the bay toward the southern end of Sandbridge. At around 4:45 pm a roof was reported blown off a house at Sandpiper and Whitecap Lane in the Sandbridge area. Two roofs were also damaged and a few trees were broken off. Damage was minimal since this is a narrow strip of land with only two streets along it. The tornado crossed the barrier island on a perpendicular (or easterly) trajectory. There were few homes and few trees with mostly beach and water in this area. A State Trooper and a few residents spotted the tornado. The tornado was rated at the lower end of an F-1 and the path length can only be estimated at 1.5 miles with a width of only 50 yards.
The Meteorology Behind the Storms
An excellent overview of the meteorological setting on 6 August 1993 was prepared by Robert Johns, the Lead Forecaster on duty at the time at the NWS National Severe Storm Forecast Center (NSSFC) in Kansas City. In his write-up of NSSFC actions that day, he described of how unusual an event this was. For an outbreak or family of tornadoes to occur in Virginia or North Carolina in mid summer, is extremely rare. Tornadoes associated with tropical cyclones (such as hurricanes) has occurred on a few occasions. However, records show that there has never been a significant outbreak of tornadoes associated with an extratropical weather system in July or August such as this one was. This type of event typically occurs in this part of the country in late April or May or during the fall months.
NSSFC highlighted the potential for severe weather in their guidance to NWS forecasts offices the day prior to the outbreak. There are three key ingredients that indicate the potential for severe thunderstorms.
1. Instability - instability is the tendency for the atmosphere to want to overturn. Warm, moist air near the surface will rise and colder, drier air aloft will sink. The more unstable the air mass, the stronger a thunderstorm's updraft will be. The stronger the updraft, the more likely it is that the storm will produce large hail and damaging winds.
2. Vertical wind shear - vertical wind shear is simply the change of wind direction and speed with height. Preferably, winds will increase with height. This helps to strengthen a storms updraft and tilt it downwind. A tilted updraft allows the rain to fall downwind. The drag from the falling rain and the rain-cooled air forms a downdraft. Because the storm is tilted, the updraft can maintain itself and the thunderstorm is able to continue to mature. A change in wind direction with height in a clockwise pattern encourages the initiation of rotation in the storms updraft and also increases the storms ability to grow and maintain itself.
3. Lift - lift is the mechanism that will trigger the development of thunderstorms. A strong lifting mechanism will help intensify and focus the storms.
A low pressure center or a front is an example of a lift mechanism.
The NWS computer models were forecasting an unstable air mass and strong southerly winds off the surface over Southeast Virginia for August 6. A warmfront and approaching low pressure center would help provide the lift. The forecasting question is "will all the ingredients come together, to what extent, and where?"
Obvious by the events of August 6, all the ingredients did come together. A warmfront moved north of Richmond. Widespread rain was occurring north of here while the area to the south was destabilizing. Temperatures climbed through the seventies as the sun peaked out from behind clouds. The air remained quite humid. Pressures fell as a low was developing along the front over Southwest Virginia and an upper level short-wave (disturbance) approached. Surfaces winds turned southeast to east at 10 to 20 mph ahead of this area and yet winds at 5000 feet were from the south-southwest at 50 to 55 mph providing the ideal vertical windshear needed for tornado development.
National Weather Service Products and Services
The National Weather Service (NWS) highlighted the potential for severe weather over southeastern Virginia early that day in a special weather statement detailing the thunderstorm potential for the state. Virginia State Emergency Operations Center was briefed via phone and NAWAS late that morning on the potential for the development of severe thunderstorms and tornadoes that afternoon in Southeast Virginia. At 12:45 pm EDT, a Tornado Watch for Southeast Virginia and Northeast North Carolina was issued. The first warning was issued for the Petersburg-Colonial Heights-Hopewell area at 1:35 pm based on a sighting of the Petersburg tornado along with weak radar indications from the NWS WSR-74 radar in Volens, Virginia.
Fifteen of the 18 tornadoes occurred within the Tornado Watch area with two more occurring very close by. Tornado Watches always state "in and near the watch area". Approximately 13 of the 18 tornadoes had warnings issued prior to touch down. Considering the difficulty of identifying these storms from radar data and the initial lack of eyewitness spotter reports to the National Weather Service, these statistics are very good. Prior to the installation of the WSR-88D in Sterling, few tornadoes in Virginia have been warned for prior to touchdown. It was unfortunate on this day that the worst tornado occurred so early in the event.
National Weather Service Radars
The National Weather Service (NWS) WSR-88D Doppler Radar in Sterling, Virginia was too far from the storms to detect the velocities within the thunderstorms and determine that they were rotating and developing tornadoes. This was partially due to the widespread area of rain between Sterling and Richmond. The Sterling radar was detecting reflectivity (large cloud droplets and rain) from these storms. However, Petersburg, for instance, is approximately 100 miles from Sterling. The lowest radar beams is angled at 0.5 degrees above the horizon meaning that as you move away from Sterling, the height of the beam increases. Add the curvature of the earth and by the time the beam reaches the storms near Petersburg, it is about 13,000 feet high. These storms only extended to 25 to 30 thousand feet so that the Sterling radar was only detecting the upper most portion of the storms. This made detection of typical severe weather and tornadic signatures very difficult.
The NWS WSR-74C in Volens, Virginia and NWS WSR-74S at Patuxent, Maryland showed little in the way of typical radar signatures for severe weather and tornadoes early in the event. Our understanding and interpretation of these signatures may change some based on this event. As the outbreak progressed and the thunderstorms moved east, the storms began to take on a more classic look. A combination of data from the older radars, the Sterling Doppler Radar and lightning data was used for determining where to issue warnings as the event progressed.
Based on experience in detecting low top rotating storms and tornadoes in northern Virginia with the Sterling radar, it is safe to say that had the WSR-88D in Wakefield, Virginia been completed, these storms would have been detected for what they were early in the event with potentially warnings being issued up to 30 minutes prior to the event. One exception was the storm that struck Petersburg. This was a new storm growing very rapidly as it approached the City. It is believed that at best there would have been a 15 minute warning time for downtown Petersburg with a WSR-88D operational in Wakefield and a radar meteorologist quick to recognize the storm for what it was. Additionally, some of that 15 minutes would have been lost in the dissemination and communication process of the warning before reaching the public.
The best method for increasing the accuracy and timeliness of severe storm warnings is to have trained severe weather spotters and emergency services personnel reporting directly to the National Weather Service Offices severe storm sightings and damage reports. Remember, a "Tornado Warning means that a tornado has been sighted or is strongly indicated by radar." Forty-five minutes prior to a tornado touching down in Petersburg was tornado damage near Kenbridge. However, this information did not reach the weather service until much later in the day. The tornado was sighted by people and even a police officer, but it was not until 1:33 pm that a report of a tornado sighted in Petersburg was relayed to the National Weather Service Richmond Office. The meteorologist at Richmond was ready when the call came in and a warning was immediately issued. However, for many, it was too late.
Another difficult feature of these storms for issuing accurate warnings using radar was the storm's tremendous tilt. What this means is that where the storm appeared on radar and where the tornado was touching the ground was a difference of a few miles. On August 6, the storms were strongly tilting to the north. The Sterling radar showed the storm that was producing a tornado in Dinwiddie County to actually be over Chesterfield County.
Without spotter reports telling the specific location of a tornado on the ground, this discrepancy with the radar location may not be realized and a warning may be issued for the wrong county or a city such as Petersburg may not be included in the warning since the storm would appear to be passing north of the city. Spotter reports and damage reports to the National Weather Service will continue to be critical to accurate warning information even after the installation of WSR-88D doppler radars around the state.
Once the new WSR-88D radars and new forecast facilities are completed in the state, the NWS ability to detect and provide early warnings will continue to improve. However, issuing a warning is only one step in the warning process. It must also be communicated and then properly responded to. In communications, there is a need for an improved Emergency Broadcast System (EBS) that will alert people who do not happen to be listening to local television or radio at that moment. The Federal Communications Commission is working on such a system. While Petersburg was equipped with sirens, sirens have been shown to be ineffective in this part of the country due to the rarity that they would be used for such an event, the frequency of malfunctions, and the fact that some people in buildings will not hear the sirens. For that reason, sirens in the Washington, D.C. Metropolitan Area have been taken down.
Even if Petersburg and Colonial Heights had had 10 to 15 minutes warning that a tornado was approaching, many people, probably including those in Wal-Mart, would not have received the warning and if they had, what would their reactions have been?
Despite recent severe weather awareness campaigns, more work is needed to teach the public proper safety actions upon seeing a tornado or receiving a warning of a tornado's approach. The actions of Wal-Mart to move people toward the front of the store (the most vulnerable area due to glass and doors) when the storm approached may have proven fatal. Not only do schools need severe weather emergency plans to direct the student body to safety, but hospitals, nursing homes, shopping malls and businesses should all have such plans that teach those with responsibility over others the proper actions to take in emergencies.
Some of the information used was obtained from newspaper accountings including the Richmond Times-Dispatch, Sunday August 8, 1993, articles written by staff writers M.W. Goodwyn and Wendy Wagner, and Beverly Orndorff. Assistance on damage surveys came from Jim Belville, Meteorologist-in-Charge of NWS Washington, D.C. Forecast Office; Peter Wolfe, Charlie Chillag and David Lipson of the NWS Richmond Weather Office; Scott Stevens of the NWS Norfolk Weather Office; Roy Brit; and John Bernier, Meteorologist with Richmond News Channel 8 for video. Robert Johns' report from NSSFC, "Tornado Outbreak of 6 August 1993" was used for some of the meteorological background. Steve Zubrick, Science Operations Officer at NWS Washington Forecast Office, for helping me proof and finalize the report and for being a Wordperfect 5.1 wiz and importing my graphics files.
A special thanks goes to Virginia Department of Emergency Services and the National Guard for assistance in conducting aerial and ground level damage surveys. Also a special thanks goes to the local emergency management officials in the independent cities and counties impacted by the storms for their cooperation and assistance in acquiring damage details and cost estimates and providing access to disaster sites.