20-foot wind speed

n. Wind speed 20 feet (six meters) above the surrounding vegetation.

 

  • Discussion

 

The standard height above the vegetation for measuring open wind speed in the United States is 20 feet; the rest of the world measures open wind speed ten meters (33 feet) above the surrounding vegetation (ten-meter wind speed). Divide 10-m wind speed by 1.15 to estimate 20-foot wind speed; multiply 20-foot wind speed by 1.15 to estimate 10-m wind speed (Turner and Lawson 1978).

 

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In forest stands, 20-foot wind speed is measured 20 feet above the top of the tree canopy, in shrublands, it is measured 20 feet above the top of the shrub vegetation.

 

20-foot wind speed is used in combination with a wind adjustment factor to estimate mid-flame wind speed.

 

  • Units

     

    Preferred units for wind speed are km/hr in technical reports and papers. Fire Management in the United States still uses the English units mi/hr. Engineering and physics applications may use units of m/s or ft/s. See the following wind speed units conversion table for conversion factors.

     

  • See Also

  • References

    • Turner, J.A.; Lawson, B.D. 1978. Weather in the Canadian Forest Fire Danger Rating System. A user guide to national standards and practices. Environment Canada, Pacific Forest Research Centre, Victoria, BC. BC-X-177.

     

  • Notes

    • Author 

      Joe Scott, Research Forester

      Systems for Environmental Management