TORRO scale

The TORRO tornado intensity scale (or T-Scale) is a scale measuring tornado intensity between T0 and T11. It was proposed by Terence Meaden of the Tornado and Storm Research Organisation (TORRO), a meteorological organisation in the United Kingdom, as an extension of the Beaufort scale.

The scale was tested from 1972 to 1975 and was made public at a meeting of the Royal Meteorological Society in 1975. The scale sets T0 as the equivalent of 8 on the Beaufort scale and is related to the Beaufort scale (B) by the formula:

and conversely:

The Beaufort scale was first introduced in 1805, and in 1921 quantified. It expresses the wind speed (v) by the formula:

Most UK tornadoes are T6 or below with the strongest known UK tornado being a T8. For comparison, the strongest detected winds in a United States tornado (during the 1999 Oklahoma tornado outbreak) would be T11 using the following formulae:

where v is wind speed and T is TORRO intensity number. Wind speed is defined as a 3-second gust at 10 m AGL.

Alternatively, the T-Scale formula may be expressed as:

or

TORRO claims it differs from the Fujita scale in that it is "purely" a wind speed scale, whereas the Fujita scale relies on damage for classification, but in practice, damage is utilised almost exclusively in both systems to infer intensity. That is because such a proxy for intensity is usually all that is available, although users of both scales would prefer direct, objective, quantitative measurements. The scale is primarily used in the United Kingdom whereas the Fujita scale is the primary scale used in North America, continental Europe, and the rest of the world.

At the 2004 European Conference on Severe Storms, Dr. Meaden proposed a unification of the TORRO and Fujita scales as the Tornado Force or TF Scale. In 2007 in the United States, the Enhanced Fujita Scale replaced the original Fujita Scale from 1971. It made substantial improvements in standardizing damage descriptors through expanding and refining damage indicators and associated degrees of damage, as well as calibrated tornado wind speeds to better match the associated damage. However, the EF Scale is biased to US construction practices,. As of 2014, only the United States and Canada have adopted the EF scale.

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