CPFM Weather & Atmospheric Conditions Flashcards

Fine dead fuel moisture below approximately what percentage significantly increases the risk of extreme fire behavior?

Answer: 5–8%

Fine dead fuel moisture below about 8% dramatically increases fire intensity and rate of spread, often warranting postponement of prescribed burns.

What time-lag fuel moisture category includes dead woody material from 1 to 3 inches in diameter?

Answer: 100-hour fuels

100-hour fuels are dead woody material ranging from 1 to 3 inches in diameter, taking approximately 100 hours to equilibrate with atmospheric moisture conditions.

Which atmospheric stability condition is most favorable for conducting a prescribed burn safely?

Answer: Stable atmosphere with good transport winds

A stable atmosphere with good transport winds limits extreme fire behavior and spotting while ensuring smoke is carried away from the burn area safely.

What does the 'dispersion index' measure in prescribed fire weather planning?

Answer: Atmosphere's capacity to dilute and transport smoke

The dispersion index quantifies the atmosphere's ability to dilute and transport smoke by combining mixing height and wind speed values.

When is it generally safest to begin ignition operations on a prescribed burn based on daily weather patterns?

Answer: Mid-morning after dew has dried but before peak afternoon heating

Mid-morning allows surface dew to dry for reliable ignition while avoiding the peak heating, low relative humidity, and atmospheric instability of afternoon hours.

What is the primary meteorological reason a prescribed burn may be postponed even when fuel moisture conditions are acceptable?

Answer: Smoke dispersal conditions are inadequate, risking air quality impacts

Even with burnable fuels, a burn may be postponed when the Ventilation Index or mixing height is too low to safely disperse smoke away from roads, communities, or sensitive areas.