Tornadoes are nature’s most violent storms, and their intensity is measured on a standardized scale based on the damage they leave behind. The most destructive events are categorized at the highest levels, with F4 and its modern equivalent, EF4, representing a degree of devastation that few structures can withstand. These ratings signify a rare class of storm, placing them among the most severe weather phenomena experienced in the United States.
The Total Historical Count
Since standardized record-keeping began in 1950, the United States has experienced over 630 violent tornadoes (F4/EF4 and F5/EF5). This figure includes both the original Fujita scale ratings and the more recent Enhanced Fujita scale ratings. The vast majority of these incidents are attributed to the F4 and EF4 category, which occur approximately nine times more frequently than the strongest F5/EF5 tornadoes. The total number of F4 and EF4 tornadoes recorded since 1950 is estimated to be between 550 and 600 events. Although exceptionally destructive, these storms still account for only about one percent of all recorded tornadoes.
Defining F4 and EF4 Tornadoes
The F4 and EF4 ratings describe the actual damage a tornado causes, which is then used to estimate the wind speeds within the storm.
F4 Rating (Original Scale)
An F4 tornado on the original scale was estimated to have wind speeds between 207 and 260 miles per hour. Damage at this level typically resulted in well-constructed houses being leveled, leaving only piles of debris. Structures with weak foundations could be blown a significant distance, and cars were often thrown.
EF4 Rating (Enhanced Scale)
The newer EF4 rating, part of the Enhanced Fujita Scale, represents a lower estimated wind speed range of 166 to 200 miles per hour. This revision was a scientific adjustment to better reflect the wind speeds required to inflict the observed damage on modern structures. An EF4 tornado is capable of completely leveling well-built frame houses. This designation represents the highest level of damage before reaching the catastrophic level of an EF5, where strong frame houses are swept clean from their foundations.
Tracking Methodology and Scale Transition
Standardized tornado record-keeping in the United States formally began in 1950, providing the historical baseline for modern tornado statistics. The classification system used for decades was the Fujita Scale (F-Scale), developed by Dr. Tetsuya Theodore Fujita in 1971. This original scale relied solely on the qualitative assessment of damage to estimate the tornado’s wind speed.
By the late 1990s, meteorologists recognized that the F-Scale had limitations, often failing to account for the quality of construction and tending to overestimate the wind speeds necessary to cause the observed damage. To address these issues, the Enhanced Fujita (EF) Scale was developed and became operational on February 1, 2007.
The EF Scale refined the process by incorporating 28 specific Damage Indicators (DIs), which include different types of structures and vegetation. These indicators allow surveyors to make a more accurate correlation between the damage and the estimated wind speed. This methodological shift explains why the historical count combines F4 and EF4 ratings: all tornadoes prior to 2007 were rated using the original F-Scale, and the two datasets are combined to maintain a continuous, long-term record.