Seasonal Percentile Distribution
Shaded: 25th–75th Percentile | Red: Selected YearWind Direction & Velocity Rose
Dominant Spread VectorsCritical Fire Danger Threshold Exceedance Days
Load data or click "Load Sample BC Dataset" to calculate threshold days.
Understanding Canadian Forest Fire Weather Index (FWI) Climatology
The Canadian Forest Fire Weather Index (FWI) System is the standard mathematical model developed by Natural Resources Canada (CWS) and used globally to estimate fire potential based solely on noon weather observations.
1. What is LTAN (Long Term Assessment of Normal)?
Fire behavior analysts in British Columbia use LTAN climatology curves to answer the critical operational question: "Are fuels and weather drier today than normal for this time of year?"
Represent normal seasonal variability. If the current year's index (red line) climbs above the grey envelope, conditions are unseasonably severe.
Statistically derived boundaries for High and Extreme wildfire potential. When indices cross the 90th percentile, fire starts frequently escape initial attack.
2. The Six Standard FWI Sub-Indices
| Index Code | Fuel Layer & Timelag | Physical Significance | Critical Levels |
|---|---|---|---|
| FFMC | Litter & cured fine fuels (~16 hour timelag) | Ease of ignition by sparks, matches, or dry lightning strikes. | ≥ 89: High; ≥ 92: Extreme |
| DMC | Loosely compacted duff (5–10cm, ~12 day timelag) | Fuel consumption in moderate duff layers and medium woody debris. | ≥ 40: High; ≥ 60: Very Dry |
| DC | Deep compact organic layers (10–20cm, ~52 day timelag) | Long-term seasonal drought indicator; predicts smoldering holdover fires. | ≥ 300: High; ≥ 450: Deep Drought |
| ISI | Combines FFMC + 10m wind velocity | Numeric rate of forward fire spread immediately after ignition. | ≥ 8: High; ≥ 15: Extreme Spread |
| BUI | Harmonic blend of DMC and DC | Total volume of fuel available for combustion in the flame front. | ≥ 60: High; ≥ 90: Heavy Fuel Dry |
| FWI | Combines ISI and BUI | Frontal fire intensity indicator (kW/m of fireline energy release). | ≥ 21: High; ≥ 31: Extreme |
3. Weather Station CSV Format Specification
When exporting from provincial weather archives or Campbell Scientific loggers, format your columns with the following standard headers:
Both hourly and daily noon snapshots are supported. Missing rows are automatically dropped from percentile quantile calculations.