A statement issued by a National Weather Service forecast office when atmospheric conditions are stable enough such that the potential exists for air pollutants to accumulate in a given area. The statement is initially issued when conditions are expected to last for at least 36 hours. 

An area on the earth's surface where atmospheric pressure is at a relative minimum. Winds blow counter-clockwise around lows in the Northern Hemisphere but, due to friction with the earth's surface, tend to cross constant pressure lines toward the low center. Upon converging into the low's center, air currents are forced to rise. As air rises it cools due to expansion. Cooling reduces its capacity to hold moisture; so cloudiness and precipitation are common in lows.

A short term for "permanently frozen ground"; any part of the earth's crust, bedrock, or soil mantle that remains below 32° F (0° C) continuously for a number of years.

Wind measured at a surface observing station, customarily at some distance (usually 20 feet) above the average vegetative surface to minimize the distorting effects of local obstacles and terrain.

The area of increased flame height and fire intensity produced when two or more fire fronts burn together.

An entity which oversees the preparedness activities for a particular ESF and coordinates with its primary and support agencies.

To be on fire.

A situation where personnel are unexpectedly caught in a fire behavior-related, life-threatening position where planned escape routes or safety zones are absent, inadequate, or compromised. An entrapment may or may not include deployment of a fire shelter for its intended purpose. These situations may or may not result in injury. They include "near misses."

Mapping unit which defines an area in terms of longitude and latitude distance. Two common scales are 1:24,000 quadrangles, which are 7.5' longitude x 7.5' latitude, and 1:62,500 quadrangles, which are 15' longitude x 15' latitude.

A pyrotechnic device specifically designed to initiate burning of a fuel mixture or propellant.