Tornado Rating Scale Comparison

The Enhanced Fujita Scale (EF Scale)

Currently used in: US (since 2007), Canada (since 2013), Mexico (adopted for research)

• Range: EF0 (65-85 mph) to EF5 (200+ mph)
• Method: Damage-based using 28 damage indicators
• 28 damage indicators covering residential to industrial structures
• Derived from Fujita Scale research updated with modern engineering

Full EF Scale explanation →

The Original Fujita Scale (F Scale)

Historical use in: US (1971-2007), most countries using historic classifications

• Range: F0 (40-72 mph) to F5 (261-318 mph)
• Method: Damage-based using descriptive damage categories
• Developed by Ted Fujita in 1971
• Wind speed estimates now considered too high by modern research

F5 vs EF5 comparison →

The TORRO Scale

Used in: UK, Ireland, parts of Europe

• Range: T0 (17-25 m/s) to T11 (117-135 m/s) - 12 levels
• Method: Wind speed direct correspondence
• Developed by Tornado and Storm Research Organisation (TORRO) in 1972
• More granular than F/EF Scale
• T11 hypothetical - no confirmed T11 event ever recorded

TORRO to F/EF Rough Equivalents

The International Fujita Scale (IF Scale)

Proposed replacement for regional scales worldwide:

• Range: IF0 to IF5 (matches EF Scale)
• Standardized damage indicators across countries
• Regional adaptations for local building materials
• Not yet officially adopted anywhere
• Would harmonize international tornado data

Adoption of the IF Scale would be a major international meteorology achievement. Debate continues about the practicality.

The Japan Meteorological Agency Scale (JMA)

Used in: Japan

• Range: F0 to F5 (matches historic Fujita)
• Japan uses the original Fujita scale largely
• Some Japanese researchers advocate switching to EF Scale

Country-by-Country Overview

United States

EF Scale since Feb 1, 2007. All events rated EF0-EF5.

Canada

EF Scale since April 1, 2013. Environment Canada issues ratings.

UK / Ireland

TORRO Scale primarily. Some events also rated F Scale for historical continuity.

France, Germany, Italy

Original Fujita Scale primarily. Some ratings use TORRO. Standardization ongoing.

Australia

Original Fujita Scale. Bureau of Meteorology (BOM) issues ratings.

Japan

Original Fujita Scale (JMA Scale).

Bangladesh

Fujita Scale. Some tornadoes are undocumented due to record limitations.

Comparing Historical Events Across Scales

To compare historical tornadoes across countries:

• Convert TORRO to EF using the rough correspondence above
• Convert original F to EF using damage-based (not wind speed) comparison
• Recognize that damage indicators differ by region
• Use engineering-based analysis for research comparisons

The Modern EF5 Drought Cross-Reference

The US EF5 drought (2013-present) can be examined internationally:

• Canada has had no EF5 since scale adoption in 2013
• Europe has had rare T5+ (F4+) events but nothing at T6+
• Japan has had no F5 since 2007 (or before)
• Bangladesh - underreported but likely has had F5-caliber events

The global "violent tornado drought" or lack of it is a subject of ongoing research.

Rating Methodology Challenges

Comparing across scales is complicated by:

• Different damage indicators by region
• Different building materials and construction quality
• Different data collection standards
• Historical documentation limitations
• Whether rating includes radar-measured winds