Path length: 14 miles
Width: 1150 yards
County: Hanson, McCook
The Spencer, SD F4 tornado of May 30, 1998 was 1 of 5 tornadoes produced by one supercell that tracked about 30 miles. This destructive tornado had a path length of 14 miles and hit the small town of Spencer (population at the time of 320) destroying most of its 190 buildings. 6 people were killed and 150 were injured. The tornado was estimated to reach a width of a mile.
Roger Edwards from the Storm Prediction Center stated in an Observations and Damage Analysis of this event that the Spencer Tornado was “the most destructive and second deadliest tornado in South Dakota history.”
This violent tornado was scanned by the OU Doppler on Wheels. Per the NWS Assessment of the event, “From 8:23 to 8:37 p.m., the Spencer tornado tracked through farmland, within 1 mile of the town of Farmer, prior to crossing the Hanson/McCook County line and striking the town of Spencer. Photographs from storm chasers show that it had grown to a large tornado west of Spencer. Apparently, it became so large that some chasers and storm spotters within 2 miles of the tornado became confused because of the large dust cloud surrounding the tornado, especially along the west and south sides where dust was raised by strong RFD winds. The DOW used by the ROTATE-98 project measured velocities of at least 90 meters per second (m/s) (200 mph) during this period.
And while the tornado passed through Spencer, “The impact time of the tornado on Spencer varies somewhat according to the source of information. Data from the ROTATE-98 project place the tornado near the western edge of town as early as 8:37 p.m., while the local electric company logged power failure in town at 8:42 p.m. and survivor accounts run as late as 8:45 p.m. Based on DOW and WSR-88D data, however, the town of Spencer experienced violent tornadic conditions from 8:38 to 8:39 p.m. Wind speeds observed by the DOW, as the tornado passed through Spencer, reached 98 m/s (nearly 220 mph) just south of the tornado center.”
Details from Storm Data
A large and strengthening tornado destroyed buildings and other property on five farms and also destroyed trees and power lines before crossing the eastern edge of Hanson County.
The tornado from Hanson County destroyed most of Spencer as it strengthened and continued to grow. Most homes, other buildings, and other structures in Spencer were completely levelled. Debris and belongings were scattered over a large area, and one receipt blown from Spencer was found just west of Chandler, MN about 80 miles east of Spencer. The tornado killed 6 and injured 150 in Spencer. The tornado continued southeast from Spencer, widened, then weakened, and dissipated 4 miles southwest of Salem with another tornado then forming from the same storm. The tornado caused additional damage to trees, power lines, crops, and buildings on farms after moving southeast of Spencer.
NIST Damage Survey Report
On May 30, 1998, at 8:38pm (CDT), a violent tornado struck the town of Spencer, South Dakota, a small farm community approximately 72 km (45 miles) west of Sioux Falls, leaving 6 dead, more than 150 injured, and nearly 90 % of a total 195 structures in the six-by-seven blocks community destroyed. Following the passage of this tornado, NIST researchers visited Spencer and conducted aerial and ground surveys to document structural damage.
The Spencer tornado left a ground track about 34 km (21 miles) long and close to a mile wide at its broadest. Based on surveys at the sites of the most severe structural damage, the National Weather Service (NWS) assigned it an F4 rating. NIST researchers conducted detailed surveys of the damage sites with the intent of providing baseline damage data to corroborate the descriptive damage associated with an F4 tornado on the Fujita scale.
Within the town of Spencer, the observed damage ranged from total disintegration of structures in the direct path of the tornado, to light damage to structural envelopes of those in the outlying areas. The completely destroyed structures included one and two-story wood-frame and light gage steel-frame constructions. Among these were wood-frame constructions that were either poorly connected to or had no connection (relying on gravity alone) to the concrete or brick foundations (this is the case with most single family homes). However, structures that were totally destroyed also included those that were properly anchored to the concrete slab-on-grade foundations by ½-in (1.3 cm) anchor bolts with proper spacing as required by current building codes (post office, fire department, gas station, antique and other stores). The town’s 36.6 m (120 ft) water tower collapsed, after being hit by a wind-borne automobile. Many heavy trucks, used in transporting grain to and from the town’s grain processing and storage warehouses (some reportedly fully loaded with grain), were lifted and carried more than 30 m away by the wind. Trucks and houses exhibited widespread evidence of missile impacts from broken wooden power poles, tree branches, and other debris.
Post-disaster investigations provide valuable information on the responses of structures to extreme loads. Complete documentation of instances of successful or poor performance can yield valuable lessons which can be used to improve construction practices. The NIST research team was coordinated by Rainer Dombrowski of the Office of Meteorological Service, National Oceanic and Atmospheric Administration (NOAA) and Robert Dumont of the Office of the Federal Coordinator for Meteorology (NOAA), and assisted by Todd Heitkamp, D. Gregory Harmon and Brian E. Smith of NWS.
The Spencer Tornado - Photo Courtesy of Roger Edwards
Radar, Tornado and Damage Photos via NWS Sioux Falls
Damage Photos via May 1998 Storm Data
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