The tornado was the third of five tornadoes that formed under the same supercell.[1] It formed after a few previous tornadoes nearby had dissipated,passing near the community of Farmer before rapidly intensifying then impacting Spencer at peak intensity. Survey results from the National Weather Service concluded that the tornado had a rating of F4 on the Fujita Scale,with winds ranging from 207–260mph (333–418km/h)[3] −however,the tornado's maximum wind speed was likely higher as a nearby Doppler on Wheels (DOW) captured wind gusts of up to 264mph (425km/h).[4]
Meteorological synopsis
A severe weather set-up was in place for May 30. A strong jet stream was approaching South Dakota,bringing winds over 50 m/s. Another jet stream was leaving the area simultaneously,creating a region of low pressure that sat atop the Missouri River. Warm,moist air extended from the southeast with cooler,dry air to the north. A cold front and dry line was also present. CAPE values were up to 4050 J/kg.[5][6] These meteorological conditions led to strong wind shear,high moisture,cool mid-level temperatures,and a capped atmosphere,leading to a significant weather event across South Dakota,producing tornadic supercells. As a result of these,the Storm Prediction Center issued a Moderate Risk for Eastern South Dakota.[6][7]
The Spencer tornado's path along with other tornadoes in South Dakota during the outbreak.
By 2300 UTC,several isolated thunderstorms formed along the dryline,including one located about 100 km west-northwest of Spencer. These supercells were observed by both the Sioux Falls WSR-88D radar and a Doppler on Wheels (DOW) mobile radar.[6] Spotter reports and an NWS damage survey suggested that five different tornadoes caused the damage in Hanson and McCook Counties,including the town of Spencer.[6][1] After an F2 rated tornado near Fulton had dissipated,the Spencer tornado would begin forming.[7]
Tornado summary
Radar loop of supercells forming over South Dakota on May 30. The green "home" location is where Spencer was located.
At 8:23 p.m. CDT,the tornado formed over rural Hanson County,northwest of Farmer. From 8:23 p.m. to 8:37 p.m.,it would move southeast over rural farm fields northwest of Spencer. It blew down a fence before knocking a few trees down[8] and impacting a farmstead at F1-F3 intensity before crossing into McCook County where Spencer was located.[9] Multiple storm chasers watched the tornado as it was approaching the community,appearing as a large,dusty,"wedge" tornado. Dust along the west and south sides of the tornado were being sucked up by strong RFD winds,confusing storm chasers and spotters observing the tornado from 2mi (3.22km) away.[10][7][11] At 8:32 p.m.,a tornado warning was issued for northern McCook County including Spencer.[9]
Track through Spencer
Between 8:38 p.m. to 8:45 p.m. CDT,the tornado impacted the community,entering town from the northwest corner.[7] Based off of damage surveys after the tornado,significant damage (F2+) extended 100-150 m north of the tornado's center. To the south of the tornado,serious damage reached 200-250 m out,ranging from F0-F4 on the Fujita Scale.[7] Six residences of the town were killed,becoming the first tornado in South Dakota to have fatalities since 1970;and also becoming the first F4 rated tornado in South Dakota since 1993. Five of the six fatalities occurred inside an apartment complex which was hit by the most violent winds [3][10] Well-constructed homes were leveled,structures with weak foundations were blown off,vehicles were thrown.[1] Nearly all 190 homes and structures in town were leveled including the town's water tower,bank,five churches,post office,fire department,nursing home,grain bins,and other businesses. A few homes around the northern portions of town were spared by the tornado. A receipt was blown from Spencer and found west of Chandler,about 80 miles east of Spencer.[10][9][12][13] It left a path of destruction of nearly 1 mile through town. Just before reaching I-90,the tornado dissipated around 5mi (8.05km) southeast of Spencer,leaving a path of approximately 14 miles (23 kilometers).[10][7][9][14]
Doppler on Wheels Observations
Throughout the entire tornado's life,a Doppler on Wheels (DOW) Mobile Radar would be observing the tornado as it moved through South Dakota,which was positioned 4km (2.49mi) west of Spencer. The DOW was close enough to the tornado to measure winds near ground level (20-40 m AGL). While the tornado was over town,5-second average winds of over 100 m/s,or roughly 225mph (362km/h) were recorded,putting it around the F4 range of wind speeds in the original Fujita Scale,and higher than the EF5 threshold for the Enhanced Fujita Scale. These wind speeds were located at the south side of the tornado's core,matching the intense damage seen after the tornado[4] F1 range of wind speeds lasted for around 120 seconds south of town,with F2,F3,and F4 winds lasting shorter and were concentrated in a narrower path,just south of the tornado's center,with F4 winds lasting 22 seconds around 50m (164ft) away south where F4 damage was reported. The DOW also recorded winds of up to 264mph (425km/h) below 50m (164ft) above the ground level around a small area,above the threshold for F5 winds in the Fujita Scale,also capturing a peak of 250mph (402km/h) on the west side of town.[4][15]
Aftermath
Just after 9:00 p.m.,the first reports of damage in Spencer was reported at the forecast office. At 9:10 p.m.,the last tornado spawned by the Spencer supercell dissipated. Details on the casualties and the amount of destruction that occurred to the town reached the forecast office after 10:00 p.m.[9][7] Ground and aerial surveys of the damage began the following day on May 31,conducted by Greg Harmon −a meteorologist in charge of the NWS Forecast Office in Sioux Falls.[9][16] On June 3,1998,the NWS officially classified the tornado with a rating of F4.
Home for senior citizens that was destroyed by the tornado.
The NWS also noted the length of the damage path to be around 14 miles (23km) long,with a maximum width of 3⁄8 mi (0.60 km) over town.[2] Emergency services responded quickly to the destruction. Among these were former Federal Emergency Management Agency(FEMA) Director James Lee Witt and former FEMA Regional Director and U.S. Senate candidate Rick Weiland. Witt −who guided the agency through 348 disasters −said that the Spencer tornado was one of the higher end of his list of worst disasters during his time in office. Weiland along with Bill Janklow coordinated to help survivors receive food,shelter,and necessities. FEMA also worked with state and local governments and voluntary organizations,such as the American Red Cross,to provide relief assistance to the victims.[17][18][19]
After the tornado,the population of Spencer,South Dakota decreased from 315 citizens to only 145.[9] The Spencer tornado was also one of the first tornadoes fully documented by Doppler On Wheels (DOW).[4] It has since been overshadowed by other tornadoes with higher wind speeds that were recorded by DOW −such as the 1999 Bridge Creek-Moore,2013 El Reno,and 2024 Greenfield tornadoes.[20] The tornado claimed a total of six,injured 153,hospitalized 41 others. 156 property owners were undecided about rebuilding,62 properties would be rebuild,16 property owners stayed at Spencer but at a different location. 12 owners wanted to lease or sell excess property. The tornado caused a total of $18 million in damages,making it the costliest in South Dakota's history.[1]
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