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Operational Awareness for Advanced Firefighters & Fire Behaviour Analysts | ||||||
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Operations staff must always monitor the setting within which they must work. In complex terrain, a key uncertainty in this arises from the interaction of wind with terrain. As winds pass over or around terrain obstacles, there may be major and dynamic variations in local wind speed and direction. Remember that wind and slope are both dominant drivers of the speed and direction of spread of a headfire. In the light winds required for fuel reduction burning it is not possible to reliably predict local winds. On-site, routine observations are essential. In the stronger winds that may be driving an escalated wildfire, it is likely that rugged lee-slopes will be carrying lee-slope eddies. It must always be remembered that somewhere on the side of a hill there may be a dynamic transition between windward and leeward wind fields. There is also a need to be watchful for wind channelling. If the prevailing winds pass over the top of an incised valley, some of the air flow is deflected downwards into the valley and sideways. The direction of deflection is determined by friction (forced channelling) or, in the case of large valleys, pressure gradients (pressure-driven channelling). Wind – terrain interactions thus may modify wind direction and speed, or may alter the general wind regime. Where needed Operations Section should issue a watchout or Red Flag Warning (Wind change). . |