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Transmission lines tower over green farmland alongside a rural road beneath a blue sky being overtaken by increasingly dark, gray clouds in the US Midwest.
Project

Determination of ice loading and tornado loading maps for transmission line design

Tornadoes and freezing rain can each cause serious damage to overhead power lines. SEI is mapping the risk these weather phenomena pose to power lines throughout the contiguous United States.

Photo: KKStock / Getty Images

Active project

2026

Project contact

Simon Mason / simon.mason@sei.org

The project aims to provide information on the risk of meteorological hazards that can cause power line disruption. Two types of hazard are being considered:

A map of the United States is divided by county, showing green blue, purple and red blobs throughout the map to indicate annual EF1 and EF2 tornado occurrences within a 20-mile radius, with EF standing for the Enhanced Fujita scale of intensity. The greatest frequency, in purple, pink and red, is shown over central Mississippi.

Average annual number of EF1 and EF2 tornadoes within a 20-mile radius. Source: SEI

  • Tornadoes: Tornadoes can cause significant damage to overhead power lines and electricity substations. We are mapping the risk posed by tornadoes in the contiguous US. We ignore both the weakest tornadoes, which are no stronger than winds associated with strong synoptic storms, and the strongest tornadoes, which are so destructive that it is not viable to design the power infrastructure to withstand them.
  • Freezing rain: Freezing rain can add significant extra load on overhead transmission lines because the rain can stick to them. We are mapping the risk posed by freezing rain in the contiguous US by estimating freezing rain accumulations for specified return periods.
Simon Mason

Senior Scientist

SEI US

Topics and subtopics
Climate : Climate services, Disaster risk
Tags
climate impacts, planning
Related centres
SEI US
Regions
United States of America

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