National Fire Danger Rating System

 What is the National Fire Danger Rating System?

The National Fire Danger Rating System (NFDRS) is a system that allows fire managers to estimate today's or tomorrow's fire danger for a given area.  It combines the effects of existing and expected states of selected fire danger factors into one or more qualitative or numeric indices that reflect an area's fire protection needs.  It links an organization's readiness level (or pre-planned fire suppression actions) to the potential fire problems of the day.

Knowledge of these levels can help forest visitors make decisions about whether or not to have a campfire or ride their OHV in a grassy area.  Homeowners may choose to postpone burning a debris pile if they are aware of the fire danger level for that day.  Contractors working in the forest may consider extra precautions when using equipment that might produce sparks.  In some cases, the National Forest may even restrict certain activities based on the fire danger levels.

Shown below is a brief explanation of the different fire danger levels, using adjectives and colors based on criteria established by the National Fire Danger Rating System.

What fire danger factors are used to get the Fire Danger Rating?

The key inputs into the NFDRS model are: fuels, weather, topography and risks. 

How is fire danger different than fire behavior predictions?

Fire danger is a broad scale assessment while fire behavior is site specific.  In other words, fire danger ratings describe conditions that reflect the potential, over a large area, for a fire to ignite, spread and require suppression action.  Fire behavior deals with an existing fire in a given time and space, describing the movement, intensity and indicators of rapid combustion of an ongoing fire.

What do you mean by "Adjective Rating"?

The "Adjective Ratings" are a public information description of the relative severity of the current fire danger situation in a general area.  Adjective Ratings are generally posted on signs as visitor enter public lands or at agency offices.  Many people associate these signs as "Smokey Bear signs".

What are the different levels and what do they mean?

We use different color-coded levels to help the public understand fire potential.  The purpose of this is for visitors to understand the current conditions and help mitigate their actions to prevent human-caused wildfires.  

Fire Weather Watch

A separate but less imminent weather forecast issued to alert fire and land management agencies to the possibility that Red Flag conditions may exist beyond the first forecast period (12 hours). The watch is issued generally 12 to 48 hours in advance of the expected conditions and may be issued up to 72 hours in advance if the NWS agency is reasonably confident. The term “Fire Weather Watch” is headlined in the routine forecast and issued as a product, similar to other primary fire warning terms. That watch then remains in effect until it expires, is canceled, or upgraded to a red flag warning.

Red Flag Warning

A forecast warning issued by the National Weather Service in the United States to inform the public, firefighters, and land management agencies that conditions are ideal for wildland fire combustion, and rapid spread. After drought conditions, when humidity is very low, and especially when there are high or erratic winds which may include lightning as a factor, the Red Flag Warning becomes a critical statement for firefighting agencies. Agencies will alter their staffing and equipment resources dramatically to accommodate the forecast risk.

· In Lake Tahoe, a Red Flag Warning means very high fire danger with increased probability of a quickly spreading vegetation fire in the area within 24 hours.

· Use of campfires, even within approved areas and Outdoor burn bans implemented.

Extreme Red Flag Warning (PDS)

Extreme Red Flag Warning (PDS) In 2019, the National Weather Service introduced an enhanced version of Red Flag Warnings, called Extreme Red Flag Warning. Analogous to the particularly dangerous situation (PDS) wording on a high-end severe weather watch, this means that conditions for fire growth and behavior are extremely dangerous due to a combination of strong winds, very low humidity, long duration, and very dry fuels.

· This indicates imminent danger, should be taken seriously communities should have a plan in place, be prepared to evacuate should a wildfire ignite.

Fire Danger Level: Low

image of fire danger sign showing When the fire danger is "low" it means that fuels do not ignite easily from small embers, but a more intense heat source, such as lightning, may start fires in duff or dry rotten wood.  Fires in open, dry grasslands may burn easily a few hours after a rain, but most wood fires will spread slowly, creeping or smoldering.  Control of fires is generally easy.

· Year-Round Fire Restrictions: Building, maintaining, attending or using a fire, campfire, or stove fire, except within the areas listed on Exhibit B in Forest Order [36 CFR 261.52(a)]

· Wood and charcoal fires in designated sites only, in agency-provided campfire rings and stoves or at recreation residence, resorts and camps as authorized in special use permit.

· Gas and petroleum jelly stoves only outside of designated sites with a valid California Campfire Permit.

· No Fireworks

· No shooting of tracer, armor piercing, steel core, or Teflon ammunition.

· Welding, grinding, cutting and use of explosives only by permit.

· Spark arrestors are required on off-highway vehicles, chainsaws, and other equipment.

 Fire Danger Level: Moderate

When the fire danger is "moderate" it means that fires can start from most accidental causes, but the number of fire starts is usually pretty low.  If a fire does start in an open, dry grassland, it will burn and spread quickly on windy days.  Most wood fires will spread slowly to moderately.  Average fire intensity will be moderate except in heavy concentrations of fuel, which may burn hot.  Fires are still not likely to become serious and are often easy to control.

· All previous restrictions apply.

· Certain geographic areas may be closed due to special circumstances.

Fire Danger Level: High

When the fire danger is "high", fires can start easily from most causes and small fuels (such as grasses and needles) will ignite readily.  Unattended campfires and brush fires are likely to escape.  Fires will spread easily, with some areas of high-intensity burning on slopes or concentrated fuels.  Fires can become serious and difficult to control unless they are put out while they are still small.

· All previous restrictions apply.

· Additional geographic areas may be closed due to special circumstances.

Fire Danger Level: Very High

When the fire danger is "very high", fires will start easily from most causes.  The fires will spread rapidly and have a quick increase in intensity, right after ignition.  Small fires can quickly become large fires and exhibit extreme fire intensity, such as long-distance spotting and fire whirls.  These fires can be difficult to control and will often become much larger and longer-lasting fires.

· All previous restrictions apply. Enhanced Fire Restrictions may be implemented which may include:

· Smoking, except within an enclosed vehicle or at a developed campground or picnic area identified in the Exempted Recreation Sites

· Operating an internal combustion engine off paved, gravel, and dirt National Forest System roads and trails, except within the Sand Pit Off-Highway Vehicle Area and boats on a water surface. 36 CFR 261.52(h)

· Welding or operating an acetylene torch with open flames, except by permit. 36 CFR 261.52(i)

· Additional geographic areas may be closed due to special circumstances.

Fire Danger Level: Extreme

When the fire danger is "extreme", fires of all types start quickly and burn intensely.  All fires are potentially serious and can spread very quickly with intense burning.  Small fires become big fires much faster than at the "very high" level.  Spot fires are probable, with long-distance spotting likely.  These fires are very difficult to fight and may become very dangerous and often last for several days.

· All previous restrictions apply. Enhanced Fire Restrictions may be implemented with the criteria listed above.

· Smoking only in enclosed vehicle or building, a developed recreation site, or while stopped in an area at least three feet in diameter that is barren or cleared of all flammable material.

· Selected recreation areas and facilities are subject to closure.

· Building, maintaining, attending or using a fire, campfire, or stove fire is prohibited in all areas including developed areas/sites.

· Forest Supervisor may designate locations with special circumstances where dispersed recreation and/or day use can be allowed. Contact the District Office for more information.

Critical 

· Entry into the Lake Tahoe Basin Management Unit National Forest System may be restricted to state and county highways. All Forest Service sites are closed during these times, EXCEPT ranger stations, fire stations, and the headquarters’ office.

· The Forest Supervisor may designate areas or certain developed sites to be open.





https://www.fs.usda.gov/detail/ltbmu/fire/?cid=fseprd584203