CPFM Weather & Atmospheric Conditions Flashcards

What wind speed range is generally considered acceptable for conducting prescribed burns?

Answer: 5–15 mph

Wind speeds of 5–15 mph are generally acceptable for prescribed burns as they provide adequate smoke dispersal without causing excessive spotting.

What atmospheric condition traps smoke near the ground by placing warm air above cooler air?

Answer: Temperature inversion

A temperature inversion reverses the normal atmospheric temperature gradient, preventing vertical mixing and trapping smoke near the surface.

What relative humidity level is typically considered the minimum threshold for safe prescribed burning?

Answer: 25–30%

Relative humidity below 25–30% significantly increases fire behavior unpredictability and the risk of losing control of a prescribed burn.

What does the Haines Index measure in relation to prescribed fire?

Answer: Potential for large fire growth

The Haines Index combines lower atmospheric stability and moisture levels to indicate the potential for large, erratic fire development.

Which weather phenomenon poses the greatest risk of causing spotting (fires starting outside the burn unit) during a prescribed burn?

Answer: Gusty, erratic winds

Gusty, erratic winds can carry burning embers unpredictably far beyond control lines, igniting spot fires outside the intended burn area.

During clear, sunny conditions, at what time of day is atmospheric instability typically greatest?

Answer: Early afternoon (1–3 PM)

Solar heating peaks in the early afternoon, creating maximum surface temperatures and strongest convective mixing, which produces the greatest atmospheric instability.