Texas Fire Weather Operation Plan - Appendix 1: Glossary

Appendix 1: Glossary

Active Crown Fire: A fire in which a solid flame develops in the crowns of trees.

Aerial Fuels: Standing and supported live and dead combustibles not in direct contact with the ground and consisting mainly of foliage, twigs, branches, stems, cones, bark and vines.

Air Transportable Modular Unit (ATMU): A weather data collection and forecasting facility used by an IMET.

Automated Surface Observing System (ASOS): The computer system which produces most of the National Weather Service surface observations.

Aspect: Direction toward which a slope faces.

Available Fuel: That portion of the total fuel that would actually burn under various environmental conditions.

Advance Weather Interactive Processing System (AWIPS): The main computer system that the National Weather Service uses to compose and transmit its forecasts and warning.

Backfire: A fire set along the inner edge of a fireline to consume the fuel in the path of a wildfire and/or change the direction of force of the fire's convective column.

Backing wind: Wind that changes direction in a counter clockwise motion.

Blowup: A sudden increase in fireline intensity or rate of spread of a fire sufficient to preclude direct control or to upset existing suppression plans. This is often accompanied by violent convection.

Burning index: An estimate of the potential difficulty of fire containment as it relates to the flame length at the head of the fire.

Burn-off temperature at 500 meters: The forecast temperature at the time in which the mixing height is expected to reach 500 meters.

Carrier fuels: The fuels that support the flaming front of the moving fire.

Chain: A unit of measure equal to 66 feet (20 meters).

County Warning and Forecast Area (CWFA): The area in which a NWS office is responsible for issuing forecasts and warnings.

Compactness: Spacing between fuel particles.

Creeping fire: A fire burning with a low flame and spreading slowly.

Crown fire: A fire that advances from top to top of trees or shrubs more or less independent of a surface fire.

Dead fuels: Fuels with no living tissue in which moisture content is governed entirely by absorption or evaporation of atmospheric moisture.

Dispersion: The decrease in concentration of airborne pollutants as they spread throughout an increasing volume of atmosphere.

Drainage wind: Normal nighttime airflow directed downslope or downvalley, caused by cooling of the air near the earth's surface. Air sinking toward lower elevations is usually quite gentle (light) in nature.

Dry lightning: A thunderstorm in which little if any precipitation occurs at the ground.

Duff: The layer of decomposing organic materials lying below the litter layer of freshly fallen twigs, needles and leaves and immediately above the mineral soil.

Effective windspeed: The midflame windspeed adjusted for the effect of slope on fire spread.

Equilibrium moisture content: Moisture content that a fuel particle will attain if exposed for an infinite period in an environment of specified constant temperature and humidity.

Extreme fire behavior: Fire behavior characterized by one or more of the following...high rate of spread...prolific crowning and/or spotting...presence of fire whirls...strong convection column.

Eye-level (six-foot) wind: Wind measured at eye level by a hand-held wind meter. These winds are affected by vegetation and terrain and are often used as mid-flame wind.

Fine fuel moisture: The moisture content of fuels such as grass, leaves, ferns, tree moss, pine needles and small twigs.

Fine (light) fuels: Fast-drying dead fuels, generally characterized by a high surface area-to-volume ratio. They have diameters 1/4 inch or less. These fuels (grass, leaves, needles, etc.) Ignite readily and are consumed rapidly by fire when dry.

Fire behavior: The manner in which a fire reacts to the influences of fuel, weather and topography.

Fire behavior forecast: A prediction of probable fire behavior, usually prepared by a fire behavior analyst in support of fire suppression or prescribed burning operations.

Fire Behavior Prediction System (FBPS): A system that uses a set of mathematical equations to predict certain aspects of fire behavior in wildland fuels when provided with data on fuel and environmental conditions.

Fire behavior analyst: Person responsible to the planning section chief for establishing a weather data collection system and for developing fire behavior predictions based on fire history, fuel, weather and topography.

Firebrand: Any source of heat, natural or human made, capable of igniting wildland fuels.

Fire danger: A general term used to express an assessment of fixed and variable factors such as fire risk, fuels, weather and topography which influence whether fires will start, spread and do damage; also the degree of control difficulty to be expected.

Fire danger rating: A fire management system that integrates the effects of selected fire danger factors into one or more qualitative or numerical indices of current protection needs.

Fire front: The part of a fire within which continuous flaming combustion is taking place.

Fire season: Period(s) of the year during which wildland fire are likely to occur, spread and affect resources value sufficient to warrant organized fire management activities.

Fire storm: Violent convection caused by a large continuous area of intense fire.

Fire weather: Weather conditions which influence fire ignition, behavior and suppression.

Fire weather service area: A geographical area of responsibility for which the local National Weather Service office provides fire weather products.

Fire weather watch: A NWS product used to alert fire fighting officials of a potential critical fire weather situation.

Fire whirl: Spinning vortex column of ascending hot air and gases rising from a fire and carrying aloft smoke, debris and flame.

Flame depth: The depth of the fire front.

Flame height: The average maximum vertical extension of flames at the leading edge of the fire front.

Flame length: The distance between the flame tip and the midpoint of the flame depth at the base of the flame; an indicator of fire intensity.

Flare-up: Any sudden acceleration in rate of spread or intensification of the fire.

Flash fuels: Fuels such as grass, leaves, draped pine needles, fern, tree moss and some kinds of slash which ignite readily and are consumed rapidly when dry.

Forecast periods

Today	Sunrise to sunset
This afternoon	Noon to 6 pm
Tonight	Sunset to sunrise
Tomorrow	6 am to 6 pm of the following day

Free-air wind: The wind above ground level and not influenced by terrain, vegetation, etc.

Fuel: Combustible material.

Fuel class: A group of fuels possessing common characteristics.

Fuel group: An identifiable association of fuel elements of distinctive species, form, size, arrangement, or other characteristics. General fuel groups are grass, brush, timber and slash.

Fuel moisture: The amount of water in a fuel, expressed as a percentage of the ovendry weight of that fuel.

Fuel moisture indicator stick: A specially prepared stick of known dry weight continuously exposed to the weather and periodically weighed to determine changes in moisture content as an indication of moisture changes in wildland fuels.

General fire weather forecast (FWF): A forecast, issued daily during the fire season, that is intended for planning purposes by land management agencies. Also called routine fire weather forecast or simply fire weather forecast.

Ground fire: Fire that consumes the organic material beneath the surface litter on the ground.

Gust: A sudden, brief increase in the speed of the wind.

Haines Index (HI): An atmospheric index used to indicate the potential for wildfire growth by measuring the stability and dryness of the air.

Head fire: A fire spreading or set to spread with the wind.

Heavy fuels: Fuels of large diameter such as logs which ignite and are consumed more slowly than flash fuels.

Holdover fire: A fire that remains dormant for a considerable time.

Hot spot: A particularly active part of a fire.

Humidity recovery: The change in relative humidity over a given period of time generally between late evening and sunrise.

Ignition probability: The chance that a firebrand will cause an ignition when it lands on receptive fuels.

Ignition temperature: The lowest temperature of a substance at which sustained combustion can be initiated.

Incident Meteorologist (IMET): A specially trained meteorologist who provides site specific weather forecasts and information to fire fighting field personnel.

Independent crown fire: A fire that advances in the tree crowns alone, not requiring any energy from the surface fire to sustain combustion or movement.

Initial attack: The actions taken by the first resources to arrive at a wildfire in order to protect life and property, and prevent further extension of the fire.

Inversion: An increase of temperature with height in the atmosphere.

Keetch-Byram Drought Index (KBDI): A drought index specifically for fire management applications. It has a numerical range from 0 (no moisture deficiency) to 800 (maximum drought).

Light fuels: See fine fuels.

Lightning Activity Level (LAL): A number, on a scale from 1 to 6, which reflects frequency and character of cloud-to-ground lightning. The scale from 1 to 5 deal with wet thunderstorms with 5 representing numerous thunderstorms with frequent lightning. 6 represents dry lightning.

Litter: The top layer of forest floor, composed of loose debris of dead sticks, branches, twigs and recently fallen leaves or needles.

Live fuel moisture: Ratio of the amount of water to the amount of dry plant material in living plants.

Live fuels: Living plants, such as trees, grasses and shrubs.

Long-range spotting: Large glowing firebrands are carried high into the convective column and then fall out downwind beyond the main fire starting new fires.

Micro-Remote Environmental Monitoring System (MICRO-REMS): A mobile weather monitoring station.

Mid-flame wind: The wind that acts directly on the flaming fire front at a level one-half the flame height.

Mixing height: The depth measured from the surface in which vigorous atmospheric mixing occurs. The mixing height is found at the base of an inversion.

Moisture of extinction: The fuel moisture content at which the fire will not spread.

National Fire Danger Rating System (NFDRS): A uniform fire danger rating system that focuses on the environmental factors that control the moisture content of fuels.

National Interagency Fire Center (NIFC): A facility located in Boise, ID, jointly operated by several federal agencies, dedicated to coordination, logistical support and improved weather services in support of fire management operations throughout the United States.

Offshore flow: Wind blowing from land to water.

One-hour fuel moisture: Moisture content of fine fuels.

One-hundred hour fuel moisture: The moisture content of dead fuels which have diameters between 1" and 3".

One-thousand hour fuel moisture: The moisture content of dead fuels which have diameters between 3" and 8".

Onshore flow: Wind blowing from water to land.

Outflow boundary: A surface boundary that is produced by thunderstorm winds.

Palmer Index: A long-term drought index which measures the moisture supply. The index is used primarily for agricultural and hydrologic concerns since it deals with evapotranspiration, soil recharge, runoff and moisture loss from the surface layer. +4 or higher means extremely wet while -4 or less means extreme drought.

Passive crown fire: A fire in the crowns of trees in which trees or groups of trees torch, ignited by the passing front of the front.

Plume-dominated wildfire: A wildland fire whose activity is determined by the convection column.

Prescribed burn: Controlled application of fire to wildland fuels in either their natural or modified state, under specified environmental conditions, which allows the fire to be confined to a predetermined area, and produce the fire behavior and fire characteristics required to attain planned fire treatment and resource management objectives.

Pressure gradient: The change in atmospheric pressure per unit distance. The greater the change in pressure per unit distance, the stronger the pressure the pressure gradient and the stronger the wind.

Presuppression: Activities in advance of fire occurrence to ensure effective suppression action. These activities include planning the organization, recruiting and training, procuring equipment and supplies, maintaining fire equipment and fire control improvements and negotiating cooperative and/or mutual aid agreements.

Probability of ignition: The chance that a firebrand will cause an ignition when it lands on receptive fuels.

Probability of Precipitation (POP)

The likelihood of a precipitation event occurring at any given point in the forecast area. A precipitation event is the occurrence of a measurable amount (0.01 inch or greater) of liquid moisture falling during a specific period in the forecast area. As guidance, an expression of uncertainty and areal qualifying terms would have the following relationship to POP values...

POP Statement Value	Expression of Uncertainty	Equivalent Areal Qualifier
<20%	slight chance	isolated, few
20%	slight chance	few, widely scattered
30-40%	chance	scattered
50%	good chance	scattered
60-70%	likely	numerous
80-100%	no remark	no remark

Rate of Spread (ROS): The relative activity of a fire in extending its horizontal dimensions.

Red flag warning: A National Weather Service product that is issued when red flag conditions (i.e., a critical fire weather situation) are expected.

Relative humidity: The ratio of the amount of moisture in the air to the maximum amount of moisture that air would contain if it were saturated.

Remote Automatic Weather Station (RAWS): An apparatus that automatically acquires, processes and stores local weather data for subsequent transmission to the GOES satellite.

Routine fire weather forecast (FWF): A forecast, issued daily during the fire season, that is intended for planning purposes by land management agencies. Also called general fire weather forecast or simply fire weather forecast.

Running fire: Behavior of a fire spreading rapidly with a well defined head.

Sea breeze boundary: A surface boundary produced by the push of marine air into the land areas.

Short-range spotting: Firebrands, flaming sparks or embers carried by surface winds which start new fires beyond the zone of direct ignition by the main fire.

Six-foot wind: See eye-level wind.

Sky cover

Clear	Zero to 1/10 opaque cloud cover.
Mostly Sunny	1/10 to 2/10 opaque cloud cover. The prevailing condition is sunny, but some clouds may be present either over a portion of the area or for a short time over the entire area.
Fair	Less than 4/10 opaque cloud cover. No precipitation. No extremes in weather, visibility, temperature, or wind.
Partly cloudy/partly sunny	3/10 to 6/10 opaque cloud cover.
Mostly cloudy/considerable cloudiness	7/10 to 8/10 opaque cloud cover. Cloudiness will be subject to some variability in amount or location.
Cloudy	9/10 or greater opaque cloud cover. The sky is essentially covered throughout the forecast period.

Slash: Debris resulting from such natural events as wind, fire or such human activities as logging, pruning or brush cutting.

Slope percent: The ratio between the amount of vertical rise of a slope and horizontal distance as expressed in a percent.

Snag: A standing dead tree or part of a dead tree from which at least the leaves and smaller branches have fallen.

Spot fire: Fire ignited outside the perimeter of the main fire by a firebrand.

Spot forecast: A specific weather forecast issued for a particular fire at a specific location.

Spotting: Behavior of a fire producing sparks or embers that are carried by the wind and which start new fires beyond the zone of direct ignition by the main fire.

Squall line: A narrow band or line of thunderstorms producing gusty winds.

Suppression: All the work of extinguishing or confining a fire beginning with its discovery.

Surface fire: Fire that burns loose debris on the surface.

Surface fuel: Fuels lying on or near the surface of the ground.

Surface trough: A narrow area of low atmospheric pressure located at the surface.

Sustained attack: Continuing fire suppression action until fire is under control.

Ten-hour fuel moisture: The moisture content of dead fuels which have diameters between ¼" and 1".

Timelag: Time needed under specified conditions for a fuel particle to lose about 63 percent of the difference between its initial moisture content and its equilibrium moisture content.

Torching: The burning of the foliage of a single tree or a small group of trees from the bottom up.

Total fuel: All plant material both living and dead that can burn in a worst case situation.

Transport winds: The mean wind speed and direction of all winds between the surface and mixing height.

Transport winds at 500 meters: The forecast transport winds at the time in which the mixing height is expected to reach 500 meters.

Tropical wave: An area of disorganized convection in the tropics.

Twenty-foot wind: Wind observed at regular RAWS/FTS observation stations, typically forecast by meteorologists, and influenced somewhat by vegetation and terrain. These winds are evaluated at either 20 feet above the surface or 20 feet above a solid layer of vegetation.

Uniform fuels: Fuels distributed continuously, thereby providing a continuous path for fire to spread.

User agency: Any agency that relies on fire weather forecast products from the National Weather Service.

Weather Information and Management System (WIMS): An interactive computer system designed to accommodate the weather information needs of federal and state natural resource management agencies.

Wetting rain: A widespread rain that over an extended period of time significantly reduces fire danger. Usually greater than 0.10".

Wildfire: An unplanned wildland fire requiring suppression action or other action according to agency policy.

Wildland: An area in which development is essentially non-existent.

Wind-driven wildland fire: A wildland fire that is controlled by a strong consistent wind.