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 NEXRADDoppler weather radar in 1990–1991.[11][note 6] 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.[15][note 4] 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.
Possibly a tornado family, this event consisted of many funnel clouds, damaging "rural property". Four remote spots north of Garden City were hit.[19][20]
This strong tornado unroofed a pair of homes, strewing debris up to 1⁄2 mi (0.80 km). One of the homes, seven rooms in all, lost its front and shifted on its foundation. A third home, then unoccupied, was wrecked as well.[10][20]
This violent tornado, the first member of a long-lived family, struck the onetime site of the National Severe Storms Laboratory (NSSL), the University of Oklahoma (OU) north campus. Scattered damage began just south of Blanchard. Well-built structures were leveled, and nine farmhouses were wrecked. Of the 48 injured were several military personnel, nine of whom were badly wounded. Near Norman the tornado damaged 10 airplanes, a dozen vehicles, and 31 buildings. Damage at OU alone totaled $600,000. The path ended near the F4–F5 Moore tornadoes in 2010 and 2013.[10][20][1]
Part of a family, this intense tornado wrecked five farmhouses and a school in the Marlow–Richland area. A trio of other homes were destroyed as well. A few semi-trailer trucks were tipped onto their sides. A pickup truck and an automobile were tossed off a road, injuring a pair of men. In all, four injuries occurred.[10][20]
A Veterans of Foreign Wars hall being built was destroyed, and a flower shop was shorn of its roof. A garage and trailer were tipped onto their sides as well. Trees in town were shredded.[19][20]
This intense tornado passed just east of Maysville, flattening barns and half a dozen farmhouses. Seven other farmhouses were damaged, and another home was wrecked near Wayne. Trucks were flipped as well. One person was injured.[10][20]
3 deaths – Related to the Norman F4, this tornado destroyed 11 homes near Shawnee Lake, resulting in a fatality. The other deaths occurred near Meeker, where the tornado wrecked farmhouses and oil derricks. The Crescent School lost its roof, allowing rain to damage its interior. Damage also affected Payson. The tornado moved a car 400 yd (1,200 ft) and its occupants 200 yd (600 ft). Eight injuries occurred.[10][20][1]
^All losses are in 1957 USD unless otherwise noted.
^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]
^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.
^ abThe 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.[4][5] Tornado ratings were retroactively applied to events prior to the formal adoption of the F-scale by the National Weather Service.[6] While the Fujita scale has been superseded by the Enhanced Fujita scale in the U.S. since February 1, 2007,[7] Canada used the old scale until April 1, 2013;[8] nations elsewhere, like the United Kingdom, apply other classifications such as the TORRO scale.[9]
^The National Oceanic and Atmospheric Administration's Storm Data publication does not list exact damage totals for every event, instead giving damage categories. As such, damage for individual tornadoes is not comprehensive.
^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.[12] Most countries only recorded tornadoes that produced severe damage or loss of life.[13] 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.[14]
^ abThe 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.[16] 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.[17][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.
— (July 1993). Significant Tornadoes 1680–1991: A Chronology and Analysis of Events. St. Johnsbury, Vermont: The Tornado Project of Environmental Films. ISBN1-879362-03-1.
— (2001b). F5-F6 Tornadoes. St. Johnsbury, Vermont: The Tornado Project of Environmental Films.
Maughan, W. E., ed. (April 1949). Written at Oklahoma City. "Tornadoes, April 30, 1949". Oklahoma section. Climatological Data. 58 (4). Washington, D.C.: United States Weather Bureau: 54.
