Fire Weather Indices
🔥 CBI as of: Sunday, June 28 2026 2:45 PM | updates every 5 minutes
🌡 FWI as of: Sunday, June 28 2026 11:00 AM | recalculated daily at noon
<25 Low • 25–50 Moderate • 50–75 High
75–90 Very High • 90+ Extreme
<5 Low • 5–10 Moderate • 10–20 High
20–30 Very High • 30+ Extreme
| Date | CBI | CBI Level | FFMC | DMC | DC | ISI | BUI | FWI | FWI Level |
|---|---|---|---|---|---|---|---|---|---|
| Sun Jun 28 | 18.7 | Low | 89.8 | 28 | 83.5 | 5.2 | 30.4 | 10.4 | High |
| Sat Jun 27 | 12.2 | Low | 89.7 | 24.7 | 73.6 | 4.6 | 26.9 | 8.7 | Moderate |
| Fri Jun 26 | 19 | Low | 89.8 | 22 | 64 | 4.8 | 23.7 | 8.4 | Moderate |
| Thu Jun 25 | 19.1 | Low | 89.7 | 18.8 | 54.3 | 5.4 | 20.1 | 8.5 | Moderate |
| Wed Jun 24 | 13.6 | Low | 89.7 | 15.5 | 44.4 | 4.9 | 16.6 | 7 | Moderate |
| Tue Jun 23 | 16.7 | Low | 89.6 | 12.6 | 34.7 | 5.7 | 13.2 | 7.1 | Moderate |
| Mon Jun 22 | 23.4 | Low | 89.6 | 9.5 | 24.8 | 5.2 | 9.7 | 5.5 | Moderate |
The Chandler Burning Index (CBI) uses air temperature and relative humidity to calculate a numerical index of fire danger, which is then mapped to a fire danger severity class of Low, Moderate, High, Very High, or Extreme. It is based solely on current weather conditions, with no adjustment for fuel moisture content.
Here on the K3JAE Weather site, the CBI is calculated from the current weather conditions observed at the station and reflects the instantaneous calculated fire danger throughout the day.
The National Weather Service also publishes a 30-day Chandler Burning Index based on forecasted weather conditions for the month. In that context, both the intensity and spread components of the index are linearly related to temperature (higher temperature = proportionately higher index) but are exponentially related to humidity — a small decrease in humidity produces a large increase in the index.
The CBI formula is:
CBI = (((110 − 1.373 × RH) − 0.54 × (10.20 − T)) × (124 × 10−0.0142 × RH)) / 60
where RH = relative humidity (%) and T = temperature (°C). Values below zero are displayed as 0 (no fire risk from weather conditions alone).
| Rating | Description |
|---|---|
| Low (L) | Fuels do not ignite readily from small firebrands, though a more intense heat source such as lightning may start fires in duff or punky wood. Fires in open cured grasslands may burn freely a few hours after rain, but woods fires spread slowly by creeping or smoldering and burn in irregular fingers. There is little danger of spotting. |
| Moderate (M) | Fires can start from most accidental causes, but the number of starts is generally low. Fires in open cured grasslands will burn briskly and spread rapidly on windy days. Timber fires spread slowly to moderately fast. Short-distance spotting may occur but is not persistent. Fires are not likely to become serious and control is relatively easy. |
| High (H) | All fine dead fuels ignite readily and fires start easily from most causes. Unattended brush and campfires are likely to escape. Fires spread rapidly and short-distance spotting is common. High-intensity burning may develop on slopes or in concentrations of fine fuels. Fires may become serious and control is difficult unless they are attacked successfully while small. |
| Very High (VH) | Fires start easily from all causes and, immediately after ignition, spread rapidly and increase quickly in intensity. Spot fires are a constant danger. Fires burning in light fuels may quickly develop high-intensity characteristics such as long-distance spotting and fire whirlwinds when they burn into heavier fuels. |
| Extreme (E) | Fires start quickly, spread furiously, and burn intensely. All fires are potentially serious. Development into high-intensity burning will usually be faster and occur from smaller fires than in the Very High class. Direct attack is rarely possible and may be dangerous except immediately after ignition. Fires in heavy slash or conifer stands may be unmanageable while extreme burning conditions last. The only effective and safe control action is on the flanks until weather changes or fuel supply lessens. |
The Fire Weather Index (FWI) is a meteorologically based numeric rating that estimates the potential intensity, ignition risk, and spread rate of wildland fires. Developed by the Canadian Forest Service, it is used globally by disaster risk managers and forestry agencies to assess daily wildfire danger based on environmental conditions.
The FWI is calculated using noon local weather observations — specifically temperature, relative humidity, wind speed, and 24-hour precipitation. Rather than measuring actual burned area, it measures how favorable weather conditions are for a fire to start and spread.
The FWI system consists of six components that build on each other to produce the final index:
- FFMC — Fine Fuel Moisture Code: Estimates the moisture content of fine surface litter such as dry twigs, needles, and leaves. High FFMC values indicate dry fuels that ignite easily and is the primary driver of fire ignition risk.
- DMC — Duff Moisture Code: Gauges the moisture of loosely compacted organic layers and medium-sized woody material beneath the surface litter. It reflects the fuel available for sustained burning deeper in the forest floor.
- DC — Drought Code: Represents the moisture content of deep, compact organic layers. It accounts for seasonal drought and the risk of smoldering and deep burning in heavy logs and peat. DC builds slowly over weeks and months and is the longest-memory component in the system.
- ISI — Initial Spread Index: Combines wind speed and FFMC to estimate the rate at which a fire might initially spread after ignition, without accounting for fuel load.
- BUI — Build-Up Index: Combines DMC and DC to represent the total amount of fuel available to sustain burning. High BUI values indicate that fires will burn with greater intensity and be harder to control.
- FWI — Fire Weather Index: The final numeric rating that combines ISI and BUI to indicate overall fire intensity and energy output at the fire front. This is the headline number used by fire agencies to communicate daily wildfire danger to the public.
Regional wildland fire agencies — such as the BC Wildfire Service and Natural Resources Canada — track these values daily to make decisions regarding suppression readiness, public safety advisories, and campfire bans. The FWI system is recognized by the World Meteorological Organization and is used in fire danger rating programs across Canada, the United States, Europe, and Australia.