From April 26–27, 1991, multiple
supercells across Oklahoma and Kansas led to a regional
tornado outbreak
__NOTOC__
A tornado outbreak is the occurrence of multiple tornadoes spawned by the same synoptic scale weather system. The number of tornadoes required to qualify as an outbreak typically are at least six to ten, with at least two rotational l ...
. Forced by a potent
trough
Trough may refer to:
In science
* Trough (geology), a long depression less steep than a trench
* Trough (meteorology), an elongated region of low atmospheric pressure
* Trough (physics), the lowest point on a wave
* Trough level (medicine), the l ...
and focused along a
dryline
A dry line (also called a dew point line, or Marfa front, after Marfa, Texas) is a line across a continent that separates moist air and dry air. One of the most prominent examples of such a separation occurs in central North America, especially T ...
, these distinct thunderstorms moved northeast through a moist and highly unstable environment. A total of 55 tornadoes were confirmed, many of which were strong, F2 or greater on the
Fujita scale. A widely documented F5 tornado tore through
Andover, Kansas
Andover is a city in Butler County, Kansas, United States, and a suburb of Wichita. As of the 2020 census, the population of the city was 14,892. Andover is the most populated city in Butler County.
History
19th century
When the Kansas te ...
, killing 17 people. Additional fatalities occurred from significant tornadoes in other portions of Kansas and Oklahoma, with 21 deaths recorded in total. An F4 tornado was detected by a mobile
doppler weather radar
Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation (meteorology), precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern wea ...
team which observed winds up to at the top of the funnel, the first time winds of F5 intensity were measured by radar, and the highest winds recorded by radar at the time. A news team filming an F2 tornado sought shelter under a
Kansas Turnpike overpass, causing a
misconception that overpasses can provide adequate shelter during a tornado. This outbreak occurred within a transition period for the
National Weather Service
The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...
and proved the value of
NEXRAD radars, which were utilized in Oklahoma to provide advanced warning to residents.
Meteorological synopsis
![1991-04-26 radar animation](https://upload.wikimedia.org/wikipedia/commons/5/59/1991-04-26_radar_animation.gif)
On April 25, 1991, the
National Weather Service
The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...
issued a warning of an impending weather system, noting that computer models were "indicating this to be a very significant severe weather producer with tornadoes occurring across the Central/Southern Plains." On the morning of April 26, the organization delineated a
High risk of severe weather across the
Great Plains
The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...
.
A southeast-tilted
trough
Trough may refer to:
In science
* Trough (geology), a long depression less steep than a trench
* Trough (meteorology), an elongated region of low atmospheric pressure
* Trough (physics), the lowest point on a wave
* Trough level (medicine), the l ...
existed across the
Southwestern United States
The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that generally includes Arizona, New Mexico, and adjacent portions of California, Colorado, Ne ...
that morning, and a distinct jet streak, or a region of enhanced winds at the base of the trough, on the order of was progressing northeast toward the Plains.
Through the morning hours, an 850
mb or approximately low-level jet of up to overspread regions from south-central Kansas northward into eastern Nebraska. A surface
low-pressure area existed over southwestern
Nebraska
Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the southwe ...
, supporting a
dry line
A dry line (also called a dew point line, or Marfa front, after Marfa, Texas) is a line across a continent that separates moist air and dry air. One of the most prominent examples of such a separation occurs in central North America, especially T ...
southward into Texas and a
warm front southeastward across eastern sections of Kansas and Oklahoma.
In the unstable atmosphere between those two boundaries, surface
dewpoints rose above . Abundant sunshine contributed to destabilization as
lifted indices topped -12 from central Oklahoma into central Kansas and
convective available potential energy reached 4,000 J/kg.
A minimal
capping inversion existed across Oklahoma even during the morning hours,
and tornado-producing storms first developed across western Oklahoma around sunrise. These storms weakened as they moved northeast into Kansas.
Back to the west, the dryline progressed rapidly eastward but began to slow precipitously during the afternoon hours. Attempts at thunderstorm development along this feature initially failed.
At 17:10 UTC (12:20 p.m. CDT), the National Weather Service issued a
particularly dangerous situation tornado watch, warning of the potential for multiple
strong to violent tornadoes. This would be one of 24 convective watches issued during the day.
Despite early failure at convective initiation,
supercell thunderstorms rapidly erupted along the dryline during the afternoon hours as the jet streak propagated into the Great Plains, resulting in a regional outbreak of tornadoes stretching from Texas to Iowa. Violent tornadoes were concentrated in southern Kansas and Oklahoma, although intense tornadoes were also observed in Iowa, Texas, and Nebraska.
Confirmed tornadoes
Haysville–McConnell AFB–Andover, Kansas
At 5:49 p.m. CDT (22:49 UTC), the storm which would become the Wichita-Andover Tornado began east of
Clearwater Clearwater or Clear Water may refer to:
Places Canada
* Clear Water Academy, a private Catholic school located in Calgary, Alberta
* Clearwater (provincial electoral district), a former provincial electoral district in Alberta
* Clearwater, Briti ...
. At 6:05 p.m. CDT (23:05 UTC), the National Weather Service issued a statement urging residents in
Haysville,
Derby
Derby ( ) is a city and unitary authority area in Derbyshire, England. It lies on the banks of the River Derwent in the south of Derbyshire, which is in the East Midlands Region. It was traditionally the county town of Derbyshire. Derby gai ...
, and
Mulvane to seek shelter. This was succeeded by a tornado warning four minutes later. Around 6:16 p.m. CDT (23:16 UTC), the intensifying tornado began to affect southeastern sections of
Wichita and directly struck Haysville.
It produced strong F2 to F3 damage in Haysville while growing to a width of about and acquiring multi-vortex characteristics. The tornado crossed the Kansas Turnpike about south of the South Wichita Interchange. In eastern Wichita, some well-built houses in the Greenwich Heights Subdivision were completely leveled, indicative of strong F3 to F4 damage. Four people were killed at this location.
At 6:24 p.m. CDT (23:24 UTC), the violent tornado struck the McConnell Air Force Base, where it narrowly missed a lineup of 10
B1-B bombers each worth $280 million and 2 of which were equipped with
nuclear warheads
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission, fission (fission bomb) or a combination of fission and nuclear fusion, fusion reactions (Thermonuclear weapon, thermonu ...
.
Nine major facilities on the base were destroyed, including the officer's club, base hospital, library, and elementary school. In addition, 102 housing units were demolished. No fatalities were recorded there, though 16 people were injured and total losses reached $62 million. As the tornado continued to move toward
U.S. Route 54 in Kansas
U.S. Route 54 (US-54) is a part of the U.S. Highway System that runs from El Paso, Texas, to Interstate 72 (I-72) in Griggsville, Illinois. In the U.S. state of Kansas, US 54 is a main east–west highway that runs from the Oklahoma bor ...
in the direction of Andover,
it prompted forecasters to issue a heightened tornado warning alerting residents in
Augusta and Andover that a damaging tornado was approaching. Despite this warning, the tornado sirens in Andover failed.
At 6:31 p.m. CDT (23:31 UTC), with the sirens not functional, the police drove through the Golden Spur Mobile Home Park and through the town warning residents to seek shelter. 10 minutes later, the large wedge-shaped tornado entered southern Andover and began to impact the mobile home park, which ultimately sustained a direct hit.
Of the 244 manufactured homes, 205, or about 84 percent of them, were destroyed. Post-storm interviews by health officials found that 339 residents were home during the tornado, of which 146 evacuated, 149 sought refuge in the community shelter, and 38 remained in their homes. No casualties occurred among individuals who fled or utilized the shelter.
However, 13 people were killed,
another 17 were hospitalized, and 9 sustained minor injuries among the group who remained in their structures.
Additional homes were swept from their foundations to the west of this park, where the Andover tornado earned its F5 rating.
Throughout the city, over 1,500 residences were devastated. The tornado continued northeast, affecting the outskirts of
Towanda. Twenty minutes later, the violent tornado dissipated west of
El Dorado
El Dorado (, ; Spanish for "the golden"), originally ''El Hombre Dorado'' ("The Golden Man") or ''El Rey Dorado'' ("The Golden King"), was the term used by the Spanish in the 16th century to describe a mythical tribal chief (''zipa'') or king o ...
and north of the Kansas Turnpike, though the parent supercell later produced additional tornadoes.
Along the tornado's path, 84 frame houses and 14 businesses were leveled. A total of 225 people were injured.
It was the final Kansas tornado to be given an F5 rating prior to the implementation of the
Enhanced Fujita Scale, which was principally used on the
Greensburg EF5 tornado on May 4, 2007.
El Dorado Lake/Kansas Turnpike Underpass, Kansas
After causing widespread destruction in Andover, the parent supercell continued northeast and produced another strong tornado. This tornado, rated F2, tracked for across Butler and Chase counties in Kansas.
It paralleled the
Kansas Turnpike for many miles before eventually crossing the road south of
Cassoday, tossing vehicles up to away from the turnpike.
The tornado gained notoriety when a Kansas television crew sought shelter underneath an overpass on the Kansas Turnpike. Video from the crew shows a minivan several hundred yards down the turnpike being rolled multiple times, with other vehicles such as large semi-trailer trucks overturned and severely damaged as well. Alongside the
1979 Wichita Falls F4 tornado, this marked the second prominent example of people seeking refuge from a tornado underneath an overpass. Information from the National Weather Service initially and indirectly contributed to this line of thought as well.
During the
1999 Oklahoma tornado outbreak
The 1999 Oklahoma tornado outbreak was a significant tornado outbreak that affected much of the Central and parts of the Eastern United States, with the highest record-breaking wind speeds of . During this week-long event, 154 tornadoes touched ...
, the consequences of this practice were realized. On May 3, 1999, there were three locations where a highway overpass was utilized as a shelter from approaching tornadoes, and at all three locations there was at least one fatality. One of these, the
1999 Bridge Creek–Moore tornado
On the evening of Monday, May 3, 1999, a large and exceptionally powerful F5 tornado registered the highest wind speeds ever measured globally; winds were recorded at by a Doppler on Wheels (DOW) radar. Considered the strongest tornado eve ...
, was at violent F4–F5 intensity as impacted the overpass. One incorrect notion from the Kansas Turnpike video was that the film crew was protected by the weaker nature of the tornado as it passed over a primarily rural area, in contrast to the Bridge Creek–Moore tornado. However, another F2 on May 3, 1999, killed one individual, proving that tornadoes of any intensity are capable of killing people harboring under overpasses. In addition to the fatalities, many people who survived these tornadoes nonetheless suffered graphic injuries and sometimes permanent disabilities. Since the Kansas Turnpike video and events on May 3, meteorologists have strongly advised people to avoid seeking shelter under highway overpasses for many reasons. One, it exposes individuals to flying debris, which is the number one cause of death in tornadoes. Two, the elevated nature of the overpass subjects people to stronger winds than at ground level. Three, overpasses may act to channel and accelerate the wind. Four, many overpasses do not have girders for individuals to hold onto, such as was the case during the Kansas Turnpike video. Fifth, tornadic winds shift directions as the vortex passes, such that people originally protected from winds will still be exposed to its effects following the wind shift. The National Weather Service therefore notes, "seeking shelter under a highway overpass is to become a stationary target for flying debris, with a substantial risk of being blown out and carried by the tornado winds". Additionally, such a move slows the flow of traffic and subjects other individuals to a potentially life-threatening situation.
Red Rock, Oklahoma
To the south of several significant supercells in Kansas, another discrete storm produced a tornado at 6:30 p.m. CDT (23:30 UTC) which would reach F4 intensity, track for , and reach a maximum width of . The tornado began east of
Garber and continued south of
Billings
Billings is the largest city in the U.S. state of Montana, with a population of 117,116 as of the 2020 census. Located in the south-central portion of the state, it is the seat of Yellowstone County and the principal city of the Billings Metrop ...
. In this area, it reached F3 intensity, snapping power poles, toppling well pumps, demolishing a house, and destroying oil tanks. As it neared
Interstate 35
Interstate 35 (I-35) is a major Interstate Highway in the central United States. As with most primary Interstates that end in a five, it is a major cross-country, north–south route. It stretches from Laredo, Texas, near the Mexican border ...
and crossed into Noble County, the tornado first reached F4 intensity, flattening a house and debarking many trees. In neighboring Osage County, two farms were destroyed before the tornado continued into Osage County. There, it passed west of
Pawhuska
Pawhuska ( osa, 𐓄𐓘𐓢𐓶𐓮𐓤𐓘 / hpahúska, ''meaning: "White Hair"'', iow, Paháhga) is a city in and the county seat of Osage County, Oklahoma, United States. It was named after the 19th-century Osage chief, ''Paw-Hiu-Skah'', wh ...
, toppling an oil rig with an foundation. It lifted west-northwest of that city.
Along the tornado's path across sparsely populated areas, several county roads had portions of their asphalt stripped away.
A
University of Oklahoma
The University of Oklahoma (OU) is a Public university, public research university in Norman, Oklahoma. Founded in 1890, it had existed in Oklahoma Territory near Indian Territory for 17 years before the two Territories became the state of Oklahom ...
chase team headed by
Howard Bluestein utilized mobile
doppler weather radar
Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation (meteorology), precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern wea ...
to analyze the tornado. The radar measured peak winds of at the top of the tornado's funnel, suggesting the tornado probably had F5 winds close to the ground. At the time, this represented the strongest winds ever measured by radar, including the first measurements of F5 intensity winds.
Aftermath
In the wake of the tornado outbreak, Kansas Governor
Joan Finney
Joan Marie Finney (née McInroy; February 12, 1925 – July 28, 2001) was an American politician who served as the 42nd governor of Kansas from 1991 to 1995. Prior to her tenure as governor, Finney served four terms as the Kansas state treasurer ...
requested that
President George H.W. Bush
George Herbert Walker BushSince around 2000, he has been usually called George H. W. Bush, Bush Senior, Bush 41 or Bush the Elder to distinguish him from his eldest son, George W. Bush, who served as the 43rd president from 2001 to 2009; pr ...
supply Sedgwick, Butler, and Cowley counties with federal disaster aid, a move that the president later approved. Under the $2.6 million program, the
Federal Emergency Management Agency
The Federal Emergency Management Agency (FEMA) is an agency of the United States Department of Homeland Security (DHS), initially created under President Jimmy Carter by Presidential Reorganization Plan No. 3 of 1978 and implemented by two Exec ...
(FEMA) paid 75 percent of the cost for disaster cleanup, while the local government paid 15 percent, and the state paid the remaining 10 percent. Oklahoma Governor
David Walters
David Lee Walters (born November 20, 1951) is an American politician who was the 24th governor of Oklahoma from 1991 to 1995.
Born in Canute, Oklahoma, Walters was a project manager for Governor David Boren and the youngest executive officer w ...
likewise requested federal assistance for six counties in his state.
American Red Cross
The American Red Cross (ARC), also known as the American National Red Cross, is a non-profit humanitarian organization that provides emergency assistance, disaster relief, and disaster preparedness education in the United States. It is the desi ...
and civil defense officials scoured devastated homes and rendered aid to about 370 families affected by the storms. After two Oklahoma counties were not granted disaster assistance, local officials in Garfield and Washington counties criticized FEMA's decision. The organization responded by noting that additional counties could be added to the list in the future but that damage in those counties was marginal for a presidential declaration. Two days later, federal assistance was made available to both counties.
In the Oologah–Talala school district of Oklahoma, which was all but devastated during the tornado outbreak, the
Oklahoma State Department of Education
The Oklahoma State Department of Education is the state education agency of the State of Oklahoma charged with determining the policies and directing the administration and supervision of the public school system of Oklahoma. The State Board of Ed ...
voted to forgive the remaining 23 days of classes, the largest number of instructional days forgiven in a single school year on record at the time. Individual student conferences were held at a local church. About 170 construction workers worked double shifts to repair the school grounds, which were tentatively set to reopen on August 12. Of the district's 24 buses, 15 were repaired in the weeks following the tornado outbreak, while 9 were rendered inoperable. The school district reopened on August 15.
The 1991 outbreak occurred during a period of modernization for the National Weather Service and helped highlight the value of radar imagery for detecting tornadoes. In April 1991, the WSR-88D NEXRAD radar in Norman, Oklahoma, was the only radar of its kind with Doppler capabilities, and even then it had not been cleared for use in day-to-day operations. In Oklahoma, the higher resolution radar displayed important storm-scale characteristics such as
mesocyclones, some of which were seen over away in Kansas. For comparison, the outdated radars in that state, though closer, did not depict significant features indicative of an ongoing tornado. Instead, forecasters in Kansas were forced to rely on reports from the public and storm chasers. In an internal assessment of the event, the National Weather Service concluded that "The NWS should continue to implement the Next Generation Radar (NEXRAD) network across the Nation. This event illustrates the usefulness of the WSR-88D velocity fields and better azimuthal resolution reflectivity data." The implementation of these radars have improved tornado lead times in modern years.
The outbreak was featured in two different documentaries: ''Enemy Wind'', a documentary produced by
The Weather Channel, and ''Cyclone'', a documentary produced and distributed by
National Geographic
''National Geographic'' (formerly the ''National Geographic Magazine'', sometimes branded as NAT GEO) is a popular American monthly magazine published by National Geographic Partners. Known for its photojournalism, it is one of the most widely ...
under its National Geographic Home Video series.
See also
*
Tornadoes of 1991
*
List of North American tornadoes and tornado outbreaks
*
List of Storm Prediction Center high risk days
Notes
References
External links
Gene Moore's April 26, 1991 Chase Account*
*
{{DEFAULTSORT:April 26, 1991, tornado outbreak
F5 tornadoes
Tornadoes of 1991
Tornadoes in Oklahoma
Tornadoes in Kansas
Butler County, Kansas
Sedgwick County, Kansas
April 26 tornado outbreak, 1991
Andover, Kansas tornado
April 1991 events in the United States