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Tornado outbreak of August 6, 1969

Damage to cabins near the current Lake Roosevelt Resort just north of Outing, Minnesota
Tornado outbreak
Tornadoes	14
Maximum rating	F4 tornado
Duration	August 6, 1969
Highest gusts	60 kn (69 mph; 110 km/h) in Iowa
Largest hail	1 in (2.5 cm) in Clearwater County, Minnesota
Overall effects
Fatalities	15+
Injuries	109
Damage	$5,120,000 ($42,540,000 in 2024 USD)
Areas affected	Minnesota Nebraska
Part of the tornadoes and tornado outbreaks of 1969

On August 6, 1969, a destructive tornado outbreak affected portions of the Upper Midwest—principally north-central Minnesota. The severe weather event generated 14 confirmed tornadoes, killed 15 people, and caused 109 injuries. To date, the outbreak remains the deadliest on record in the North Woods region of Minnesota. It is also known as the 1969 Minnesota tornado outbreak and the 1969 North Woods tornado outbreak. The most destructive tornado of the outbreak was a 33-mile-long (53 km) violent F4 that leveled miles of timberland and farmland across portions of Crow Wing, Cass, and Aitkin counties in Minnesota, killing at least 12 people and injuring 70 others.

Background

Very warm, humid, summertime air had pushed into central and southern Minnesota on August 6, 1969. Minneapolis recorded a high temperature of 93 °F (34 °C) with dew points near 70 °F (21 °C). Meanwhile, strong upper-level winds over northern Minnesota and an approaching cold front from the west added the needed ingredient for the strong storms. Two distinct thunderstorms formed approximately 45 mi (72 km) apart and tracked east-northeastward across Minnesota at 50 mph (80 km/h). These parallel storms generated 14 tornadoes, killing 15 people and injuring 109.

The first tornado of the day, rated F0, touched down at 1:15 p.m. CDT (12:15 p.m. CST; 18:15 UTC) in Beltrami County. The main tornado event started about three hours later in Cass County when an F3 tornado touched down southwest of Backus, injuring four people. The most damaging tornado of the outbreak touched down at 4:48 p.m. CDT (3:48 p.m. CST; 21:48 UTC) in Crow Wing County. It achieved F4 strength, traveling 33 miles (53 km) through Crow Wing, Cass and Aitkin counties. The area around Outing was especially hard hit by this tornado, where 11 deaths and 40 injuries occurred on the shores of Roosevelt Lake.

Several more strong tornadoes touched down over the next two hours, killing one person near Jacobson and two people near Two Harbors. Damage and casualties were limited, however, because most of the twisters, however large in size, struck rural areas.

Confirmed tornadoes

{{efn|Prior to 1990, there is a likely undercount of tornadoes, particularly E/F0–1, with reports of weaker tornadoes becoming more common as population increased. A sharp increase in the annual average E/F0–1 count by approximately 200 tornadoes was noted upon the implementation of NEXRAD Doppler weather radar in 1990–1991. 1974 marked the first year where significant tornado (E/F2+) counts became homogenous with contemporary values, attributed to the consistent implementation of Fujita scale assessments. Numerous discrepancies on the details of tornadoes in this outbreak exist between sources. The total count of tornadoes and ratings differs from various agencies accordingly. The list below documents information from the most contemporary official sources alongside assessments from tornado historian Thomas P. Grazulis.

See also

• Climate of Minnesota
• List of North American tornadoes and tornado outbreaks
• Tornadoes of 1969

Notes

1. All losses are in 1969 USD unless otherwise noted.
2. An outbreak is generally defined as a group of at least six tornadoes (the number sometimes varies slightly according to local climatology) with no more than a six-hour gap between individual tornadoes. An outbreak sequence, prior to (after) the start of modern records in 1950, is defined as a period of no more than two (one) consecutive days without at least one significant (F2 or stronger) tornado.
3. Historically, the number of tornadoes globally and in the United States was and is likely underrepresented: research by Grazulis on annual tornado activity suggests that, as of 2001, only 53% of yearly U.S. tornadoes were officially recorded. Documentation of tornadoes outside the United States was historically less exhaustive, owing to the lack of monitors in many nations and, in some cases, to internal political controls on public information. Most countries only recorded tornadoes that produced severe damage or loss of life. Significant low biases in U.S. tornado counts likely occurred through the early 1990s, when advanced NEXRAD was first installed and the National Weather Service began comprehensively verifying tornado occurrences.
4. The Fujita scale was devised under the aegis of scientist T. Theodore Fujita in the early 1970s. Prior to the advent of the scale in 1971, tornadoes in the United States were officially unrated. Tornado ratings were retroactively applied to events prior to the formal adoption of the F-scale by the National Weather Service. While the Fujita scale has been superseded by the Enhanced Fujita scale in the U.S. since February 1, 2007, Canada used the old scale until April 1, 2013; nations elsewhere, like the United Kingdom, apply other classifications such as the TORRO scale.
5. All starting coordinates are based on the NCEI database and may not reflect contemporary analyses
6. All dates are based on the local time zone where the tornado touched down; however, all times are in Coordinated Universal Time and dates are split at midnight CST/CDT for consistency.
7. The listed width values are primarily the average/mean width of the tornadoes, with those having known maximum widths denoted by ♯. From 1952 to 1994, reports largely list mean width whereas contemporary years list maximum width. Values provided by Grazulis are the average width, with estimates being rounded down (i.e. 0.5 mi (0.80 km) is rounded down from 880 yards to 800 yards.

References

1. Storm Data Publication 1969, Events reported
2. Storm Data Publication 1969, Events reported
3. ^ "Northwoods Tornado Outbreak August 6, 1969". NWS Weather Forecast Office Duluth, MN. Duluth, Minnesota: National Weather Service. 2019. Archived from the original on August 6, 2019. Retrieved September 11, 2019.
4. Haskins, Austin (August 6, 2019). "Tuesday marks 50th anniversary of deadliest tornado outbreak in northern Minnesota". KBJR6.com. Duluth, Minnesota: KBJR-TV. Archived from the original on August 6, 2019. Retrieved September 17, 2019.
5. Schneider, Russell S.; Brooks, Harold E.; Schaefer, Joseph T. (2004). Tornado Outbreak Day Sequences: Historic Events and Climatology (1875–2003) (PDF). 22nd Conf. Severe Local Storms. Hyannis, Massachusetts: American Meteorological Society. Retrieved September 17, 2019.
6. ^ Kuehnast 1969, p. 128.
7. ^ Storm Data Publication 1969, #10055652
8. ^ Storm Data Publication 1969, #10055654
9. ^ Grazulis 1984, p. A-80.
10. Agee and Childs 2014, p. 1496.
11. Grazulis 2001a, pp. 251–4.
12. Edwards, Roger (March 5, 2015). "The Online Tornado FAQ (by Roger Edwards, SPC)". Storm Prediction Center: Frequently Asked Questions about Tornadoes. Storm Prediction Center. Retrieved February 25, 2016.
13. Cook & Schaefer 2008, p. 3135.
14. Agee and Childs 2014, pp. 1497, 1503.
15. Grazulis 1993, p. 141.
16. Grazulis 2001a, p. 131.
17. Edwards et al. 2013, p. 641–642.
18. Edwards, Roger (March 5, 2015). "Enhanced F Scale for Tornado Damage". The Online Tornado FAQ (by Roger Edwards, SPC). Storm Prediction Center. Retrieved February 25, 2016.
19. "Enhanced Fujita Scale (EF-Scale)". Environment and Climate Change Canada. Environment and Climate Change Canada. June 6, 2013. Archived from the original on March 3, 2016. Retrieved February 25, 2016.
20. "The International Tornado Intensity Scale". Tornado and Storm Research Organisation. Tornado and Storm Research Organisation. 2016. Archived from the original on March 5, 2016. Retrieved February 25, 2016.
21. Agee and Childs 2014, p. 1494.
22. Brooks 2004, p. 310.
23. Grazulis 1990, p. ix.
24. ^ "Severe Weather Database Files (1950-2021)". Storm Prediction Center Maps, Graphics, and Data Page. Norman, Oklahoma: Storm Prediction Center. July 11, 2021. Retrieved February 24, 2022.
25. ^ USWB 1969, p. 121.
26. ^ Grazulis 1993, p. 1106.
27. Storm Data Publication 1969, #10055655
28. Storm Data Publication 1969, #10055656
29. Storm Data Publication 1969, #10055657
30. ^ USWB 1969, p. 122.
31. Storm Data Publication 1969, #10055658
32. Storm Data Publication 1969, #10055659
33. ^ Grazulis 1993, pp. 1106–7.
34. Storm Data Publication 1969, #10055660
35. Storm Data Publication 1969, #10055661
36. ^ Grazulis 1993, p. 1107.
37. Storm Data Publication 1969, #10055662
38. Storm Data Publication 1969, #10055663
39. Storm Data Publication 1969, #10055664
40. Kuehnast 1969, p. 129.
41. Storm Data Publication 1969, Events reported
42. Storm Data Publication 1969, #10055665
43. Storm Data Publication 1969, #10055666
44. Storm Data Publication 1969, #10067866
45. USWB 1969, p. 123.

Sources

• Agee, Ernest M.; Childs, Samuel (June 1, 2014). "Adjustments in Tornado Counts, F-Scale Intensity, and Path Width for Assessing Significant Tornado Destruction". Journal of Applied Meteorology and Climatology. 53 (6). American Meteorological Society: 1494–1505. doi:10.1175/JAMC-D-13-0235.1.
• Brooks, Harold E. (April 2004). "On the Relationship of Tornado Path Length and Width to Intensity". Weather and Forecasting. 19 (2): 310–19. Bibcode:2004WtFor..19..310B. doi:10.1175/1520-0434(2004)019<0310:OTROTP>2.0.CO;2.
• Cook, A. R.; Schaefer, J. T. (August 2008). "The Relation of El Niño–Southern Oscillation (ENSO) to Winter Tornado Outbreaks". Monthly Weather Review. 136 (8): 3121–3137. Bibcode:2008MWRv..136.3121C. doi:10.1175/2007MWR2171.1.
• Edwards, Roger; LaDue, James G.; Ferree, John T.; Scharfenberg, Kevin; Maier, Chris; Coulbourne, William L. (May 1, 2013). "Tornado Intensity Estimation: Past, Present, and Future". Bulletin of the American Meteorological Society. 94 (5). American Meteorological Society: 641–653. doi:10.1175/BAMS-D-11-00006.1.
• Grazulis, Thomas P. (May 1984). Violent Tornado Climatography, 1880–1982. OSTI (Technical report). NUREG. Washington, D.C.: Nuclear Regulatory Commission. OSTI 7099491. CR-3670.
  • — (November 1990). Significant Tornadoes 1880–1989. Vol. 2. St. Johnsbury, Vermont: The Tornado Project of Environmental Films. ISBN 1-879362-02-3.
  • — (July 1993). Significant Tornadoes 1680–1991: A Chronology and Analysis of Events. St. Johnsbury, Vermont: The Tornado Project of Environmental Films. ISBN 1-879362-03-1.
  • — (2001a). The Tornado: Nature's Ultimate Windstorm. Norman: University of Oklahoma Press. ISBN 978-0-8061-3538-0.
  • — (2001b). F5-F6 Tornadoes. St. Johnsbury, Vermont: The Tornado Project of Environmental Films.
• National Weather Service (August 1969). Storm Data Publication (Report). National Centers for Environmental Information – via Storm Events Database.
• Kuehnast, Earl L. (August 1969). Written at Saint Paul, Minnesota. "The Different Behavior Patterns of Twelve Tornadoes Occurring August 6, 1969". Special Weather Summary. Climatological Data. Minnesota. 75 (8). Asheville, North Carolina: National Climatic Data Center: 128–9.
• U.S. Weather Bureau (August 1969). "Storm Data and Unusual Weather Phenomena". Storm Data. 11 (8). Asheville, North Carolina: National Climatic Data Center.

External links

• Minnesota Tornado History and Statistics
• Gendisasters.com

• F4 tornadoes by date
• F4 tornadoes by location
• Tornadoes of 1969
• Tornadoes in Minnesota
• Tornadoes in Nebraska
• 1969 in Minnesota
• August 1969 events in the United States