WILDFIRE: LATEST LEARNINGS- v01.6

WILDFIRE: LATEST LEARNINGS

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General learning outcome:

SPECIFIC HIGH COUNTRY WEATHER:

Specific learning outcome:

Subsidence inversions and nocturnal low-level jets can invert the diurnal weather cycle.

Topic:

The formation of a subsidence inversion and its potential impacts on surface fire weather.

Operational Awareness for Advanced Firefighters & Fire Behaviour Analysts


The thermal expansion of middle layers of the air can push warm, dry air downwards towards the surface. The highest ground, above say 1500m ASL, will be impacted by this first. Upper air frequently has very low dew point temperatures, unaffected by the evaporation of water from the surface. Thus even though the temperature at these heights may be much lower than in the lowlands, the relative humidity can be very low say 10%.This can reduce fuel moisture content to dangerous conditions. If, as is common on high ground, the wind speeds are elevated, then the FDI can be elevated as well.
Most importantly this often happens between midnight and sunrise, inverting the typical daily FDI cycle. Records show that this can happen on between one day in six and one day in nine. Thus over the course of a campiagn fire it is very likely to happen.
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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.