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Meteorological synopsis

On April 25, 1991, the National Weather Service 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. A southeast-tilted trough existed across the Southwestern United States that morning, and a distinct jet streak, or a region of enhanced winds at the base of the trough, on the order of 75–85 kn (85–100 mph; 140–155 km/h) was progressing northeast toward the Plains. Through the morning hours, an 850 mb or approximately 5,000 ft (1,525 m) low-level jet of up to 60 kn (70 mph; 110 km/h) overspread regions from south-central Kansas northward into eastern Nebraska. A surface low-pressure area existed over southwestern Nebraska, supporting a dry line 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 60 °F (15 °C). 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.

Haysville–McConnell AFB–Wichita–Andover, Kansas

Haysville–McConnell AFB–Wichita–Andover, Kansas

Severe damage to trees from the tornado
Meteorological history
Formed	April 26, 1991, 5:49 p.m. CDT (UTC−05:00)
Dissipated	April 26, 1991, 7:14 p.m. CDT (UTC−05:00)
Duration	1 hour and 25 minutes
F5 tornado
on the Fujita scale
Highest winds	>261 mph (420 km/h)
Overall effects
Casualties	17 fatalities, 225 injuries
Damage	$300 million ($671,100,000 in 2024 USD)

At 5:49 p.m. CDT (22:49 UTC), the storm which would become the Wichita–Andover tornado began east of Clearwater. At 6:05 p.m. CDT (23:05 UTC), the National Weather Service issued a statement urging residents in Haysville, Derby, 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 220 yards (200 m) and acquiring multi-vortex characteristics. The tornado crossed the Kansas Turnpike about 0.5 miles (0.80 km) 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 B-1B bombers each worth $280 million and 2 of which were equipped with nuclear warheads. 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 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 now large wedge-stovepipe hybrid 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 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.

1. ^ "The Kansas-Oklahoma Tornado Outbreak of April 26, 1991". Oklahoma Climatological Survey. Retrieved April 20, 2022.
2. ^ "25th Anniversary of April 26th, 1991 Tornado Outbreak". National Weather Service. National Weather Service in Wichita, Kansas. Retrieved April 20, 2022.
3. Cody Moore. "Andover, KS Tornado Outbreak April 26, 1991" (PDF). University of Louisville. Retrieved April 20, 2022.
4. Dan McCarthy (April 26, 1991). "Day 1 Convective Outlook". Iowa Environmental Mesonet. Retrieved April 25, 2022.
5. ^ "The April 26, 1991 Great Plains Tornado Outbreak". National Weather Service. National Weather Service in Norman, Oklahoma. Retrieved April 20, 2022.
6. ^ "Top Ten KS Tornadoes". National Weather Service. National Weather Service in Wichita, Kansas. Retrieved April 23, 2022.
7. ^ "Timeline for supercell that produced the Wichita/Andover Tornado". National Weather Service. National Weather Service in Wichita, Kansas. Retrieved April 23, 2022.
8. NWS Wichita (May 3, 2016). "#Andover25th tornado struck Haysville as a strong F2/F3. #Outbreak1991" (Tweet). Retrieved April 23, 2022 – via Twitter.
9. ^ "Review of major tornadoes across south central Kansas on April 26 1991". National Weather Service. National Weather Service in Wichita, Kansas. Retrieved April 23, 2022.
10. NWS Wichita (May 3, 2016). "When the #Andover25th tornado hit the McConnell AFB, it missed a lineup of B1-B bombers. #Outbreak1991" (Tweet). Retrieved April 23, 2022 – via Twitter.
11. NWS Wichita (May 3, 2016). "The #Andover25th damaged/destroyed 9 major facilities causing $62 million in damages. #Outbreak1991" (Tweet). Retrieved April 23, 2022 – via Twitter.
12. NWS Wichita (May 3, 2016). "On 4/26/91 @6:30p Tornado warning issued for Andover - tornado sirens in Andover failed #Andover25th #Outbreak1991" (Tweet). Retrieved April 23, 2022 – via Twitter.
13. ^ Centers for Disease Control (CDC) (March 13, 1992). "Tornado Disaster — Kansas, 1991". Morbidity and Mortality Weekly Report. 41 (10): 181–183. JSTOR 23299145. PMID 1538688.
14. Craig Torbenson; Sadonia Corns; Jessica Nellis; Keith Wondra (November 28, 2011). Kansas: In the Heart of Tornado Alley. Arcadia Publishing. ISBN 978-1-4396-4193-4. Retrieved April 23, 2022.
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