A tornado is a violently rotating column of air that extends from a thunderstorm and makes contact with the ground. Because these atmospheric phenomena vary significantly in power, size, and duration, a standardized system is needed to measure their intensity and the resulting damage. In the United States, the current method for classifying a tornado’s strength is the Enhanced Fujita Scale, often shortened to the EF Scale. This scale allows meteorologists and engineers to consistently assess the impact of these storms after they have passed through an area.
The Enhanced Fujita Scale
The EF Scale is a six-point system that assigns a rating from EF0, representing the weakest measurable damage, up to EF5, which indicates the most destructive events. This system replaced the original Fujita Scale in 2007 to provide a more accurate correlation between wind speed and the damage inflicted on various structures and vegetation. The EF rating is not determined by real-time wind measurements; instead, it is assigned only after a tornado event based on a thorough damage survey conducted by trained personnel.
The survey process involves identifying specific markers known as Damage Indicators (DIs), which include residential homes, mobile homes, trees, and steel-framed buildings. For each of the 28 Damage Indicators, there are multiple Degrees of Damage (DODs) that correlate the physical destruction with an estimated wind speed range. This methodology accounts for differences in construction quality, ensuring the final rating is a more precise estimate of the tornado’s true power.
Defining the EF0 Tornado
The EF0 tornado is the lowest classification on the Enhanced Fujita Scale, often categorized as a “weak” or “gale” intensity storm. The estimated three-second gust wind speeds associated with an EF0 rating range from 65 to 85 miles per hour (mph). These wind speeds are still equivalent to or greater than those found in a tropical storm or a Category 1 hurricane at its lowest threshold.
This classification is the most common type of tornado observed in the United States, accounting for over half of all recorded events. While individually less destructive, EF0 tornadoes are a routine part of the severe weather landscape. The rating is assigned when damage to the most vulnerable structures and objects is observed, though well-built structures typically remain largely intact.
Typical Damage Caused by an EF0
The physical evidence that leads to an EF0 rating is generally limited to light damage, primarily affecting non-structural elements and vegetation. Common signs include the loss of roof shingles, minor damage to siding or gutters, and damage to chimneys. Carports, sheds, or other lightweight outbuildings might also be slightly damaged or shifted.
In terms of vegetation, an EF0 tornado is strong enough to break small branches off trees and push over shallow-rooted trees. While major structures are usually unscathed, the resulting debris, such as falling tree limbs or broken signs, can still pose a safety risk. The damage is noticeable but does not involve the collapse of walls or the complete destruction of any substantial structure.