Downward or sinking motion of air in the atmosphere. Subsiding air warms due to compression. Increasing temperature and decreasing humidities are present in subsiding air. Subsidence results in a stable atmosphere inhibiting dispersion. Subsidence is generally associated with high atmospheric pressure. 

An apparent force due to the rotation of the earth that causes a deflection of air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This force maximizes at the poles and is essentially zero at the equator.

Fire pattern that resembles a U or V shape and indicates the direction of fire progression in that area. One of the 11 NWCG categories of fire pattern indicators.

Part of the National Fire Danger Rating System (NFDRS).  Number used to determine seasonal risk class for a protection unit, calculated by multiplying peak monthly average by two and adding seasonal monthly average.

The number of years between two successive fire events for a given area; also referred to as fire-free interval or fire-return interval.

Total amount of heat produced per unit mass of fuel consumed per unit time.

The rapid oxidation of fuel in which heat and usually flame are produced. Combustion can be divided into four phases: preignition, flaming, smoldering, and glowing.

A hand operated instrument for obtaining wet and dry bulb temperature readings and, subsequently, relative humidity.

A preplanned and understood route firefighters take to move to a safety zone or other low-risk area. When escape routes deviate from a defined physical path, they should be clearly marked (flagged).

Analysis of factors which influence suppression of an escaped fire from which a plan of attack will be developed; includes development of alternative strategies of fire suppression and net effect of each.