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 potential wind regimes around rugged terrain and the prevailing weather that can produce them.

Expert Awareness for Advanced Firefighters & Fire Behaviour Analysts


It is essential that staff in a Situation Unit consider the potential wind fields. Key possibilities are:
  • Light winds where wind direction is little affected by terrain, and winds accelerate on exposed faces and decelerate on leeward faces.
  • Moderate winds, where winds may or may not be deflected by terrain. Field observations are essential.
  • Strong prevailing winds – over 25 km/hr – will produce dominant lee-slope eddies.
It must also be remembered that major terrain features may alter the wind flow before localised wind-terrain interactions are factored in. Thus a WNW wind may become a NW on the lee of a major ridge system, and this is the wind that is affected by localised interactions with a prominent hilltop.
Analysts need to continually monitor the balance between prevailing winds, wind terrain interactions, thermal winds and wind channelling.
Consideration should be given to issuing a watchout (Wind change at fire) if winds become variable or erratic.
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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.