Term frequently used in aviation operations, usually in connection with a stated altitude.

Sum of constant danger and variable danger factors affecting the inception, spread, and resistance to control, and subsequent fire damage; often expressed as an index.

A widespread rain that over an extended period of time significantly reduces fire danger. One-tenth of an inch may be sufficient to reduce fire danger in grass fuel models. One half inch may be necessary for timber fuels under closed canopies.

In NFDRS, the two grass types (annual, perennial) determine how seasonal drying of live herbaceous fuels is modeled.

Any nonfrontal line or narrow band of active thunderstorms extending across the horizon. It is of importance to fire behavior due to accompanying strong gusty winds and the possibility of such a line passing between regular weather observation stations without being reported.

Any treatment of living and dead fuels that reduces the potential spread or consequences of fire.

Resources assigned to an incident but unable to respond for mechanical, rest, or personal reasons.

A helicopter equipped with a fixed tank, Airtanker Board certified, capable of delivering a minimum of 1,100 gallons of water, foam, or retardant.

Work performed by an individual employee in support of an incident while remaining at the employee’s duty station or other designated off-site location.

Crystals of ice formed and deposited like dew, but at a temperature below freezing.