WILDFIRE: LATEST LEARNINGS- v01.6

WILDFIRE: LATEST LEARNINGS

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General learning outcome:

SPECIFIC HIGH COUNTRY WEATHER:

Specific learning outcome:

When prevailing winds exceed 25km/hr lee-eddy winds may become important.

Topic:

The conditions for dominance of lee-slope eddies.

Expert Awareness for Advanced Firefighters & Fire Behaviour Analysts


In general terms the formation of a lee-slope eddy requires undulating or rugged terrain. The lee slope should generally be above 10Ý, but this varies with prevailing wind speed. The aspect should be opposite to the wind direction to within about 50Ý. Long runs with continuous slope and aspect values are able to support stronger eddies than complex slopes. Under some situations eddies are stationary, in others they roll over the terrain.
Eddies always have a separation point, where they stop following the terrain and rise up to loop back. Outside the eddy there may be prevailing winds or channelled winds (depending on where it lies in the toposequence).
When wind speeds are assessed as able to produce lee-slope eddies, consideration should be given to issuing a watchout (Wind change at fire).
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This website is dedicated to bringing forward the latest research findings. They are provided to allow firefighters to be made aware of critical safety issues ahead of the material being included in the national training curriculum.
Material prepared by Rick McRae for AFAC Research Dissemination Pilot Study, March 2012.