Tornado outbreak sequence of April 30–May 2, 1967

A destructive severe weather episode affected portions of the Midwestern and Southern United States from April 30–May 2, 1967. It consisted of two consecutive tornado outbreaks that generated at least 38 tornadoes, causing 13 fatalities and 90 injuries. All of the deaths occurred on April 30, which is known as the 1967 Iowa–Minnesota tornado outbreak, or Black Sunday, to residents of Iowa and southern Minnesota. That day spawned a total of 21 tornadoes, devastating the towns of Albert Lea and Waseca, Minnesota.[6][7][nb 2][nb 3]

Tornado outbreak sequence of April 30–May 2, 1967
A home leveled to its foundation in Waseca, Minnesota
TypeTornado outbreak sequence
DurationApril 30–May 2, 1967
Tornadoes confirmed38 confirmed[1][2]
Max. rating1F4 tornado
Duration of tornado outbreak22 days, 2 hours, and 55 minutes
Highest gust70 kn (81 mph; 130 km/h) in Louisiana on May 1[3]
Largest hail2 3⁄4 in (7.0 cm) in diameter in Pittsburgh County, Oklahoma, on April 30[4]
Damage$286.982 million (1967 USD)[nb 1][5]
$2.2 billion (2021 USD)
Casualties13 fatalities, 90 injuries
Areas affectedMidwestern and Southern United States (particularly Iowa and Minnesota)

1Most severe tornado damage; see Fujita scale
2Time from first tornado to last tornado

Background
Surface weather analysis for April 30, 1967, at 1:00 a.m. EST (06:00 UTC), the morning prior to the tornado outbreak.

Beginning on April 30, 1967, a potent mid-latitude cyclone generated severe weather, including blizzards and severe thunderstorms, across a broad region extending from the northernmost High Plains and Rocky Mountains to the Mississippi and Ohio River valleys. These conditions occurred within a seventy-two-hour-long span.[18] By 1:00 p.m. CDT (12:00 p.m. CST; 18:00 UTC) on April 30, a low-pressure area of at most 984 millibars (29.06 inHg) was centered near Pierre, South Dakota, with a stationary front superimposed from north of Sioux Falls to near LaCrosse, Wisconsin. Nearby, a warm front also attended from south of Sioux Falls to near Des Moines, Iowa, and St. Louis, Missouri.[19] As the warm sector advanced into northernmost Iowa and southern Minnesota, surface air temperatures rose into the 60s and low 70s °F, while dew points reached the 60s °F. Winds at the surface ranged from 15 to 25 miles per hour (24 to 40 km/h) out of the east-southeast.[19] By 7:00 p.m. CDT (6:00 p.m. CST; 00:00 UTC), the warm front migrated to near the Minnesota-Iowa border, while the mid-level trough associated with the surface cyclone acquired a negative tilt. At the same time, a strong jet stream brought deep-layer wind shear over portions of northern Iowa and southern Minnesota—indicating favorable conditions for tornadogenesis.[20]

Daily statistics
Confirmed tornadoes by Fujita rating
FU F0 F1 F2 F3 F4 F5 Total
0 1 8 21 4 4 0 38
"FU" denotes unclassified but confirmed tornadoes.
Daily statistics of tornadoes produced by the tornado outbreak sequence of April 30–May 2, 1967
Date Total Fujita scale rating Deaths Injuries Damage Ref.
 FU   F0   F1   F2   F3   F4   F5 
April 30 21 0 0 4 10 3 4 0 13 81 ≥$11,000,000 [5][21][22][23]
May 1 15 0 1 5 8 1 0 0 0 9 ≥$25,000 [5][14][24]
May 2 2 0 0 0 2 0 0 0 0 0 $25,000 [5][14][24]
Total 38 0 1 8 21 4 4 0 13 90 $286,962,000 [5][14][22][24]
Outbreak death toll[5]
State Total County County
total
Minnesota 13 Freeborn 7
Waseca 6
Totals 13
All deaths were tornado-related

Confirmed tornadoes

April 30 event
List of confirmed tornadoes – Sunday, April 30, 1967[5][nb 4][nb 5]
F# Location County / Parish State Start
coord.		 Time (UTC) Path length Max. width Summary Refs.
F1 NW of De Smet Kingsbury SD 44.40°N 97.57°W / 44.40; -97.57 (De Smet (April 30, F1)) 21:15–? 0.1 miles (0.16 km) 10 yards (9.1 m) A brief tornado struck unpopulated countryside, resulting in no material damage. [26]
F2 NW of Vincent to ENE of Thor Webster IA 42.60°N 94.03°W / 42.60; -94.03 (Eagle Grove (April 30, F2)) 21:50–? 6.8 miles (10.9 km) 200 yards (180 m) Tornado researcher Thomas P. Grazulis did not list this tornado as an F2 or stronger. [14]
F2 ESE of Gruver to SE of Huntington Emmet IA 43.38°N 94.68°W / 43.38; -94.68 (Huntington (April 30, F2)) 22:00–? 8.2 miles (13.2 km) 300 yards (270 m) This tornado struck six barns, one of which was destroyed. Damage was also reported in Dolliver. [27][28]
F2 Emmetsburg to WNW of Ringsted Palo Alto, Emmet IA 43.12°N 94.67°W / 43.12; -94.67 (Halfa (April 30, F2)) 22:10–? 14 miles (23 km) 300 yards (270 m) This tornado struck the western portion of the community of Halfa, tearing the roofs off several homes. While passing east of Gridley, it also destroyed barns. [28]
F2 WSW of Crystal Lake Hancock, Winnebago IA 43.22°N 93.80°W / 43.22; -93.80 (Crystal Lake (April 30, F2)) 22:30–? 4.3 miles (6.9 km) 300 yards (270 m) This tornado struck eight farmsteads, three of which were nearly destroyed, except for the farmhouses. [28]
F2 NNE of Gruver Emmet IA 43.42°N 94.68°W / 43.42; -94.68 (Gruver (April 30, F2)) 22:33–? 1 mile (1.6 km) 200 yards (180 m) Grazulis did not list this tornado as an F2 or stronger. [14]
F3 Clear Lake Cerro Gordo IA 43.10°N 93.42°W / 43.10; -93.42 (Clear Lake (April 30, F3)) 23:05–? 7.7 miles (12.4 km) 250 yards (230 m) This tornado destroyed barns, agricultural machinery, and one home. Observers reported three distinct funnel clouds. Grazulis listed the tornado as an F2. [28][27]
F2 Fort Madison Lee IA 40.63°N 91.32°W / 40.63; -91.32 (Fort Madison (April 30, F2)) 23:20–? 2.3 miles (3.7 km) 400 yards (370 m) Grazulis did not list this tornado as an F2 or stronger. [14]
F4 ENE of Manly to SSE of Otranto Worth IA 43.30°N 93.17°W / 43.30; -93.17 (Manly (April 30, F4)) 23:28–? 13.3 miles (21.4 km) 400 yards (370 m) This violent tornado caused extensive damage to approximately ten farms. [28]
F3 SSE of Kensett to N of London, MN Worth (IA), Freeborn (MN) IA, MN 43.33°N 93.20°W / 43.33; -93.20 (Kensett (April 30, F3)) 23:30–? 17.2 miles (27.7 km) 800 yards (730 m) This tornado caused extensive damage to six farmsteads and destroyed a few homes. [29]
F2 W of Lemond to NE of Waseca Waseca MN 43.98°N 93.42°W / 43.98; -93.42 (Lemond (April 30, F2)) 00:00–? 9.2 miles (14.8 km) 67 yards (61 m) This tornado destroyed barns as it passed near Lemond and west of Meriden. The total path length may have been 30 miles (48 km). [28]
F1 WSW of Union Steele MN 43.87°N 93.20°W / 43.87; -93.20 (Ellendale (April 30, F1)) 00:05–? 0.2 miles (0.32 km) 10 yards (9.1 m) N/A N/A
F3 Alden to ESE of Matawan Freeborn, Waseca MN 43.67°N 93.58°W / 43.67; -93.58 (Alden (April 30, F3)) 00:05–? 14 miles (23 km) 100 yards (91 m) 2 deaths – Near the start of its path, this tornado neared the threshold of F4-level intensity, based on structural damage to farms. Additionally, the tornado destroyed barns. Twenty-three people sustained injuries. [30][28]
F4 ENE of Northwood to ENE of Myrtle, MN Worth (IA), Freeborn (MN) IA, MN 43.45°N 93.17°W / 43.45; -93.17 (Myrtle (April 30, F4)) 00:20–? 7.6 miles (12.2 km) 500 yards (460 m) This powerful tornado destroyed ten farms in Minnesota, three of which sustained borderline-F5-level damage. One injury was reported. [31][28]
F4 NNW of Twin Lakes to Albert Lea to Owatonna Freeborn, Steele MN 43.57°N 93.43°W / 43.57; -93.43 (Albert Lea (April 30, F4)) 00:23–? 38.7 miles (62.3 km) 100 yards (91 m) 5 deaths – This destructive, long-tracked tornado caused $2 million in damages in Albert Lea alone. The tornado ravaged the western portion of the town; there, it significantly damaged 55 homes, and "completely leveled" 10 others. In all, the tornado destroyed 26 homes and severely damaged an additional 64 in Albert Lea. Along its entire path, the tornado flattened farms at six different locations. The tornado also destroyed many structures on farms near Owatonna. The tornado injured a total of 35 people. [32][29][33]
F4 W of Hartland to NNE of Waseca Freeborn, Waseca MN 43.80°N 93.52°W / 43.80; -93.52 (Hartland (April 30, F4)) 00:52–? 20.1 miles (32.3 km) 267 yards (244 m) 6 deaths – This tornado was the last violent event of the entire outbreak sequence. It paralleled Minnesota State Highway 13, known then as Highway 67, and damaged farms on each side of the highway. In Waseca, the tornado leveled six homes, destroyed 16, and extensively damaged 25. The tornado injured 22 people. [34][29]
F1 NW of Littleton Buchanan IA 42.55°N 92.05°W / 42.55; -92.05 (Littleton (April 30, F1)) 01:00–? 0.1 miles (0.16 km) 50 yards (46 m) N/A N/A
F1 NW of Montezuma Poweshiek IA 41.60°N 92.55°W / 41.60; -92.55 (Montezuma (April 30, F1)) 01:00–? 0.1 miles (0.16 km) 10 yards (9.1 m) N/A N/A
F2 SE of Austin to E of Nicolville Mower MN 43.63°N 92.93°W / 43.63; -92.93 (Austin (April 30, F2)) 01:15–? 3.8 miles (6.1 km) 10 yards (9.1 m) This short-lived tornado destroyed a few barns and unroofed a home on a farmstead. [29]
F2 S of Marion to N of Eyota Olmsted MN 43.93°N 92.35°W / 43.93; -92.35 (Marion (April 30, F2)) 02:10–02:15 6.8 miles (10.9 km) 10 yards (9.1 m) This tornado destroyed a barn and a trailer. [29]
F2 SSE of Epworth Dubuque IA 42.40°N 90.90°W / 42.40; -90.90 (Epworth (April 30, F2)) 03:00–? 2 miles (3.2 km) 400 yards (370 m) Grazulis did not list this tornado as an F2 or stronger. [14]

May 1 event
List of confirmed tornadoes – Monday, May 1, 1967[5][nb 4][nb 5]
F# Location County / Parish State Start Coord. Time (UTC) Path length Max. width Summary Refs.
F2 E of North Zulch Madison TX 30.92°N 96.08°W / 30.92; -96.08 (North Zulch (May 1, F2)) 12:00–? 0.6 miles (0.97 km) 33 yards (30 m) A brief tornado destroyed a barn and a livestock pen. Fencing was wrenched from the ground as well. Grazulis did not list this tornado as an F2 or stronger. [14][35]
F1 NNW of Lambert Hot Spring AR 34.35°N 93.23°W / 34.35; -93.23 (Lambert (May 1, F1)) 13:20–? 0.1 miles (0.16 km) 10 yards (9.1 m) A brief tornado felled many trees and damaged one home. [36]
F2 WSW of Ebenezer Camp TX 32.95°N 94.92°W / 32.95; -94.92 (Ebenezer (May 1, F2)) 13:30–? 1 mile (1.6 km) 50 yards (46 m) A brief tornado destroyed a pair of chicken coops and damaged a number of large livestock feeders. Trees were downed as well. Grazulis did not list this tornado as an F2 or stronger. [14][35]
F1 Mount Pleasant Wood TX 33.17°N 94.97°W / 33.17; -94.97 (Mount Pleasant (May 1, F1)) 16:00–? 0.1 miles (0.16 km) 10 yards (9.1 m) A brief tornado damaged several buildings and a farmhouse on up to six farmsteads. Trees were uprooted as well. [35]
F2 NNE of Corsicana Navarro TX 32.17°N 96.45°W / 32.17; -96.45 (Corsicana (May 1, F2)) 16:00–? 2 miles (3.2 km) 33 yards (30 m) A brief tornado, coincident and possibly in conjunction with downbursts, flipped a mobile home and damaged or destroyed a few houses and several barns. A large pecan was prostrated as well. Grazulis did not list this tornado as an F2 or stronger. [14][35]
F0 SSE of Avinger Cass TX 32.88°N 94.55°W / 32.88; -94.55 (Avinger (May 1, F0)) 17:00–? 0.5 miles (0.80 km) 300 yards (270 m) A brief tornado sheared and uprooted trees beside a church. [35]
F1 W of Negreet Sabine LA 31.47°N 93.60°W / 31.47; -93.60 (Negreet (May 1, F1)) 18:50–? 1 mile (1.6 km) 33 yards (30 m) A tornado was observed but did not produce damage. [37]
F2 E of Symonds Bolivar MS 33.83°N 90.85°W / 33.83; -90.85 (Symonds (May 1, F2)) 19:45–? 1 mile (1.6 km) 200 yards (180 m) A brief tornado affected a 600-acre (240 ha) conservation area as it tossed and sank forty motorboats, some of which were wrapped around trees. Additionally, the tornado tore a section from a 200-foot-long (61 m) pier, severely damaged several trees, and tilted a concession stand. Grazulis did not list this tornado as an F2 or stronger. [14][38]
F2 Onalaska to W of Leggett Polk TX 30.80°N 95.12°W / 30.80; -95.12 (Onalaska (May 1, F2)) 20:00–20:10 8 miles (13 km) 67 yards (61 m) This tornado may have first begun in Point Blank, on the opposite shore of the Trinity River. In and near Point Blank, trees sustained damage, a church was destroyed, and homes were damaged. However, official data indicate that the tornado first impacted Onalaska, on the eastern side of Lake Livingston. In Onalaska, the tornado unroofed a combined store and post office; the building itself also lost its rear wall. The tornado injured two people, and losses reached $25,000. Onalaska would be hit again on April 22, 2020, when an even stronger EF3 tornado killed three and injured 33 others in the town. [39][40][41][29]
F1 W of Hazel Calloway KY 36.50°N 88.35°W / 36.50; -88.35 (Hazel (May 1, F1)) 20:15–? 1 mile (1.6 km) 50 yards (46 m) A brief tornado destroyed one house and minimally damaged a few others. Some outbuildings and trees were levelled as well. [42]
F2 NNE of Dayton Liberty TX 30.07°N 94.88°W / 30.07; -94.88 (Dayton (May 1, F2)) 23:45–00:00 1.5 miles (2.4 km) 33 yards (30 m) A brief tornado caused sizeable damage to trees, splintered utility poles, and partly unroofed a building. Several other structures were substantially damaged, one of which had its steel doors knocked down. Additionally, a horse died as a barn collapsed during the tornado. Grazulis did not list this tornado as an F2 or stronger. [14][43]
F3 Mittie Allen LA 30.67°N 92.93°W / 30.67; -92.93 (Mittie (May 1, F3)) 00:15–? 5.2 miles (8.4 km) 750 yards (690 m) An intense tornado damaged or destroyed homes, sheds, barns, and trees. Two people sustained injuries, one of which was critical. [29][37][44]
F2 S of Geronimo Guadalupe TX 29.65°N 97.97°W / 29.65; -97.97 (Geronimo (May 1, F2)) 02:45–? 0.5 miles (0.80 km) 20 yards (18 m) A brief tornado tore the roof off a home and destroyed a barn nearby. [29][43]
F2 Kaplan Vermilion LA 30.00°N 92.28°W / 30.00; -92.28 (Kaplan (May 1, F2)) 04:40–? 2 miles (3.2 km) 50 yards (46 m) A brief tornado affected 35 homes and businesses as it passed through Kaplan. Four people were injured. Grazulis did not list this tornado as an F2 or stronger. [14][37][45]

May 2 event
List of confirmed tornadoes – Tuesday, May 2, 1967[5][nb 4][nb 5]
F# Location County / Parish State Start Coord. Time (UTC) Path length Max. width Summary Refs.
F2 E of Bayou Pigeon Iberville LA 30.08°N 91.22°W / 30.08; -91.22 (Bayou Pigeon (May 1, F2)) 05:30–? 1 mile (1.6 km) 50 yards (46 m) A brief tornado destroyed a mobile home and a delicatessen. A nearby home and a pilothouse also incurred damage. One person was injured. [46][29][37]
F2 SSE of Lucedale George MS 30.90°N 88.58°W / 30.90; -88.58 (Lucedale (May 2, F2)) 07:25–? 0.1 miles (0.16 km) 10 yards (9.1 m) A brief tornado dislodged a house, flipped a nearby mobile home, and downed a large tree. A utility room and a carport were torn loose as well. Grazulis did not list this tornado as an F2 or stronger. [14][38]
F2 Dunean Greenville SC 34.83°N 82.42°W / 34.83; -82.42 (Dunean (May 2, F2)) 00:10–? 1 mile (1.6 km) 67 yards (61 m) A brief tornado significantly damaged three homes and slightly damaged about forty others. Windows, signage, and canopy-forming vegetation were broken. Grazulis did not list this tornado as an F2 or stronger. [14][47]

See also

Notes
  1. All losses are in 1967 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.[8][9][10][11][12][13]
  3. 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.[14] While the Fujita scale has been superseded by the Enhanced Fujita scale in the U.S. since February 1, 2007,[15] Canada utilized the old scale until April 1, 2013;[16] nations elsewhere, like the United Kingdom, apply other classifications such as the TORRO scale.[17]
  4. 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.
  5. Prior to 1994, only the average widths of tornado paths were officially listed.[25]

References
  1. National Weather Service (30 September 2019). Grazulis, Thomas P.; Grazulis, Doris (eds.). Tornado History Project: Maps and Statistics. Tornado History Project (Report). The Tornado Project of Environmental Films. Retrieved 2 January 2021.
  2. National Weather Service (30 September 2019). Grazulis, Thomas P.; Grazulis, Doris (eds.). Tornado History Project: Maps and Statistics. Tornado History Project (Report). The Tornado Project of Environmental Films. Retrieved 2 January 2021.
  3. National Weather Service (May 2019). Events reported between 04/30/1967 and 05/02/1967 (3 days). Storm Events Database (Report). National Centers for Environmental Information. Retrieved 18 November 2019.
  4. National Weather Service (May 2019). Events reported between 04/30/1967 and 05/02/1967 (3 days). Storm Events Database (Report). National Centers for Environmental Information. Retrieved 18 November 2019.
  5. National Weather Service (May 2019). Events reported between 04/30/1967 and 05/02/1967 (3 days). Storm Events Database (Report). National Centers for Environmental Information. Retrieved 24 September 2019.
  6. Hatfield, Karen (2007). "Black Sunday April 30, 1967". National Weather Service Weather Forecast Office Twin Cities, MN. Minneapolis–Saint Paul: National Weather Service. Archived from the original on 12 October 2012. Retrieved 23 September 2019.
  7. Hatfield, Karen (2017) [2007]. Krause, Tom (ed.). The April 30, 1967 Tornadoes in Southern Minnesota: A Retrospective (PDF) (Report) (Revised ed.). National Weather Service. Archived from the original (PDF) on 12 September 2017. Retrieved 23 September 2019.
  8. Schneider, Russell S.; Brooks, Harold E.; Schaefer, Joseph T. (2004). Tornado Outbreak Day Sequences: Historic Events and Climatology (1875-2003) (PDF). 22nd Conference on Severe Local Storms. Hyannis, Massachusetts: American Meteorological Society. Retrieved 17 September 2019.
  9. Hagemeyer, Bartlett C. (September 1997). "Peninsular Florida Tornado Outbreaks". Weather and Forecasting. Boston: American Meteorological Society. 12 (3): 400. Bibcode:1997WtFor..12..399H. doi:10.1175/1520-0434(1997)012<0399:PFTO>2.0.CO;2.
  10. Grazulis 2001, p. 206
  11. Hagemeyer 1997, p. 401
  12. Hagemeyer, Bartlett C.; Spratt, Scott M. (2002). Written at Melbourne, Florida. Thirty Years After Hurricane Agnes: the Forgotten Florida Tornado Disaster (PDF). 25th Conference on Hurricanes and Tropical Meteorology. San Diego, California: American Meteorological Society. Archived from the original (PDF) on 16 October 2008. Retrieved 24 November 2019.
  13. Grazulis, Thomas P. (2001). The Tornado: Nature's Ultimate Windstorm. Norman: University of Oklahoma Press. p. 206. ISBN 978-0-8061-3538-0.
  14. Grazulis, Thomas P. (July 1993). Significant Tornadoes 1680–1991: A Chronology and Analysis of Events. St. Johnsbury, Vermont: The Tornado Project of Environmental Films. p. 141. ISBN 1-879362-03-1.
  15. Edwards, Roger (5 March 2015). "Enhanced F Scale for Tornado Damage". The Online Tornado FAQ (by Roger Edwards, SPC). Storm Prediction Center. Retrieved 25 February 2016.
  16. "Enhanced Fujita Scale (EF-Scale)". Environment and Climate Change Canada. Environment and Climate Change Canada. 6 June 2013. Archived from the original on 25 February 2016. Retrieved 25 February 2016.
  17. "The International Tornado Intensity Scale". Tornado and Storm Research Organisation. Tornado and Storm Research Organisation. 2016. Archived from the original on 25 February 2016. Retrieved 25 February 2016.
  18. Hatfield 2017, p. 7
  19. Hatfield 2017, p. 10
  20. Hatfield 2017, p. 15
  21. Grazulis, Thomas P. (July 1993). Significant Tornadoes 1680–1991: A Chronology and Analysis of Events. St. Johnsbury, Vermont: The Tornado Project of Environmental Films. pp. 1089–90. ISBN 1-879362-03-1.
  22. U.S. Weather Bureau (April 1967). "Storm Data and Unusual Weather Phenomena". Storm Data. Asheville, North Carolina: National Climatic Data Center. 9 (4): 27, 30, 36.
  23. Hatfield 2017, p. 14
  24. U.S. Weather Bureau (May 1967). "Storm Data and Unusual Weather Phenomena". Storm Data. Asheville, North Carolina: National Climatic Data Center. 9 (5): 42, 45–7, 52, 54–5.
  25. Brooks, Harold E. (April 2004). "On the Relationship of Tornado Path Length and Width to Intensity". Weather and Forecasting. Boston: American Meteorological Society. 19 (2): 310. Bibcode:2004WtFor..19..310B. doi:10.1175/1520-0434(2004)019<0310:OTROTP>2.0.CO;2.
  26. USWB 1967a, p. 36
  27. USWB 1967a, p. 27
  28. Grazulis 1993, p. 1089
  29. Grazulis 1993, p. 1090
  30. National Weather Service (May 2019). Minnesota Event Report: F3 Tornado. Storm Events Database (Report). National Centers for Environmental Information. Retrieved 26 September 2019.
  31. National Weather Service (May 2019). Iowa Event Report: F4 Tornado. Storm Events Database (Report). National Centers for Environmental Information. Retrieved 26 September 2019.
  32. National Weather Service (May 2019). Minnesota Event Report: F4 Tornado. Storm Events Database (Report). National Centers for Environmental Information. Retrieved 26 September 2019.
  33. Hatfield 2017, p. 22
  34. National Weather Service (May 2019). Minnesota Event Report: F4 Tornado. Storm Events Database (Report). National Centers for Environmental Information. Retrieved 26 September 2019.
  35. USWB 1967b, p. 54
  36. USWB 1967b, p. 42
  37. USWB 1967b, p. 46
  38. USWB 1967b, p. 47
  39. "NWS Damage Survey for April 22 2020 Polk County Tornado Event". Iowa Environmental Mesonet. National Weather Service Weather Forecast Office in Houston, Texas. April 24, 2020. Retrieved April 24, 2020.
  40. USWB 1967b, pp. 54–5
  41. National Weather Service (May 2019). Texas Event Report: F2 Tornado. Storm Events Database (Report). National Centers for Environmental Information. Retrieved 14 November 2019.
  42. USWB 1967b, p. 45
  43. USWB 1967b, p. 55
  44. National Weather Service (May 2019). Louisiana Event Report: F3 Tornado. Storm Events Database (Report). National Centers for Environmental Information. Retrieved 14 November 2019.
  45. National Weather Service (May 2019). Louisiana Event Report: F2 Tornado. Storm Events Database (Report). National Centers for Environmental Information. Retrieved 14 November 2019.
  46. National Weather Service (May 2019). Louisiana Event Report: F2 Tornado. Storm Events Database (Report). National Centers for Environmental Information. Retrieved 14 November 2019.
  47. USWB 1967b, p. 52
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