Understanding the Metrics
Every metric in your Wildfire Intelligence Report is drawn from federal data and rated using published fire agency standards. This page explains what each one measures and why it matters.
Fire Danger Class
The headline badge on your report. Rates current fire danger at your location on a five-level scale from Low to Extreme, updated every day by the US Forest Service.
This is a relative rating, not an absolute one. The rating reflects where today's conditions fall compared to the full historical record for your specific area. "High" in the foothills outside Los Angeles and "High" in coastal Oregon represent the same degree of danger relative to what's normal in each place — not the same absolute weather conditions. This matters because fire behavior in different landscapes requires different baselines to be meaningful.
The rating is computed by the USFS from a gridded weather model at ~10 km resolution — the same data behind the national WFAS fire danger map used by federal dispatch centers. It covers the entire country and is calibrated station-by-station using decades of historical fire weather records.
| Level | Threshold | What it means |
|---|---|---|
| Extreme | ≥ 97th percentile | Historically rare conditions. Fire starts easily, spreads rapidly, and is difficult to control. |
| Very High | ≥ 92nd percentile | Well above average. Firefighting effectiveness is significantly reduced. |
| High | ≥ 79th percentile | Above average. Fires start and spread quickly under these conditions. |
| Moderate | ≥ 58th percentile | Elevated above normal. Fire is possible but manageable under most conditions. |
| Low | < 58th percentile | Normal or below. Fire behavior is limited. |
Source: USFS Rocky Mountain Research Station — WFAS ERCPercCls raster, published daily. Class breaks confirmed from WFAS SPL documentation.
Energy Release Component (ERC)
ERC measures the total heat energy that would be released per square foot of fuel bed if a fire started at your location. It combines moisture from all fuel types — fine grasses, medium sticks, large logs, and live vegetation — into a single number.
ERC is shown as a percentile — relative to historical norms at the nearest weather station. A 90th percentile ERC means conditions are drier and hotter than 90% of all days ever recorded at that station. This makes it comparable across different climates and locations. The absolute ERC number (in BTU/sq ft) varies widely by region and isn't shown because it isn't interpretable without local context.
Because ERC doesn't include wind, it's more stable day-to-day than other indices — making it the standard planning tool used by federal dispatch centers for pre-positioning crews and equipment 1–3 days ahead.
Source: NIFC NFDRS FeatureServer (nearest RAWS station). Thresholds match WFAS ERCPercCls raster class breaks (NWCG PMS 437).
Burning Index (BI)
BI estimates the potential flame length at a fire's leading edge. Higher wind speeds produce a higher BI — a BI of 40 corresponds to roughly 4-foot flame lengths.
Like ERC, BI is shown as a percentile relative to the station's historical record. Unlike ERC, BI does factor in wind — which makes it a useful real-time indicator but means it can swing dramatically with afternoon gusts. Your report shows BI alongside ERC as a corroborating signal. When both are elevated, the case for high danger is stronger. When they diverge, conditions are dynamic — check the wind card.
Source: NIFC NFDRS FeatureServer (nearest RAWS station). Confirmed definition: NWCG PMS 437.
100-hr Fuel Moisture
Measures the moisture content of dead wood 1–3 inches in diameter — sticks and small branches. These fuels respond to weather changes over days to a week, not hours.
This is an absolute measurement in percent moisture — not a percentile. The thresholds (8%, 10%, 15%, 20%) mean the same thing everywhere regardless of location. Below 10%, fuels are considered critically dry by NWCG standards — fires start easily under any ignition source and spread rapidly. Above 20%, these fuels are unlikely to sustain fire without prolonged exposure.
| Level | Threshold | What it means |
|---|---|---|
| Extreme | < 8% | Critically dry. Fuels ignite under any spark. Aggressive fire behavior expected. |
| Very High | < 10% | At or near the critically dry threshold. Fire behavior severely elevated. |
| High | < 15% | Approaching critical range. Elevated rate of spread. |
| Moderate | < 20% | Below average moisture. Some drying effect on fire behavior. |
| Low | ≥ 20% | Normal or above. Fine to medium fuels are not a primary risk factor. |
Source: WFAS MC100 raster (USFS RMRS, CONUS coverage, daily). Thresholds: NWCG PMS 410-1 (Fireline Handbook).
1000-hr Fuel Moisture
Measures moisture in large dead wood — logs and heavy branches 3–8 inches in diameter. These fuels take weeks to months to dry out, and they're the primary driver of how long and how intensely a fire burns.
This is an absolute measurement — the thresholds mean the same thing everywhere. When 1000-hr moisture drops below 15%, large fuels can sustain overnight burning. Fires no longer die down after sunset, which is when most containment work happens. Extended drought is the main driver, which is why this metric and KBDI often track together.
| Level | Threshold | What it means |
|---|---|---|
| Extreme | < 10% | Critically dry. Fires burn through the night and are extremely difficult to contain. |
| Very High | < 15% | Large fuels dry enough for sustained overnight burning. |
| High | < 20% | Elevated large-fuel drying. Increased fire duration. |
| Moderate | < 30% | Approaching below-average moisture. |
| Low | ≥ 30% | Normal or above. Large fuels are not a significant fire factor. |
Source: WFAS MC1000 raster (USFS RMRS, CONUS coverage, daily). Thresholds: NWCG PMS 410-1 (Fireline Handbook).
Relative Humidity
The percentage of moisture in the air at your location. Low humidity accelerates the drying of fine fuels — grass, leaves, and small sticks — in real time.
Most NWS Red Flag Warning criteria for California and the western US require RH below 15%. Combined with wind, low RH creates conditions where a fire can escape control within minutes. Note that your 100-hr and 1000-hr fuel moisture values reflect accumulated drying over days and weeks — RH tells you what's happening right now.
| Level | Threshold | What it means |
|---|---|---|
| Extreme | < 10% | Extremely dry air. Fuels desiccating rapidly. Highest ignition risk. |
| Very High | < 15% | NWS Red Flag Warning threshold for most of California and the western US. |
| High | < 25% | Approaching Red Flag criteria. Fine fuels drying quickly. |
| Moderate | < 40% | Below average. Some drying effect on fine fuels. |
| Low | ≥ 40% | Adequate humidity. Limited drying effect on fuels. |
Source: Open-Meteo forecast API. Thresholds anchored to NWS Instruction 10-204 Red Flag criteria (western US representative).
Drought Index (KBDI)
The Keetch-Byram Drought Index measures soil and fuel moisture deficit on a 0–800 scale — designed specifically for wildfire applications, not agricultural drought. Zero means soils are fully saturated; 800 means all available moisture is depleted.
KBDI is updated daily at roughly 10 km resolution and responds to individual rain events, making it more timely than the weekly Drought Monitor for tracking fire-relevant conditions. High KBDI values mean deep fuels and soils are dry — fires burn deeper, produce more heat, and are significantly harder to mop up after the flame front passes.
| Level | Threshold | What it means |
|---|---|---|
| Extreme | ≥ 600 | Severe fire drought. Maximum fire behavior. Containment extremely difficult. |
| Very High | ≥ 500 | Approaching extreme. Deep fuels critically dry. |
| High | ≥ 400 | Significant drought. Fire intensity and duration substantially elevated. |
| Moderate | ≥ 200 | Moderate drought. Noticeable effect on fire behavior. |
| Low | < 200 | Below significant drought threshold. Moisture deficit is limited. |
Source: WFAS KBDI raster (USFS RMRS, CONUS coverage, daily). Thresholds: USFS RMRS KBDI documentation.
Drought Monitor (D0–D4)
The USDA Drought Monitor is the official federal drought classification, jointly produced by USDA, NOAA, and the University of Nebraska–Lincoln. Updated weekly at the county level. Classifications run from D0 (Abnormally Dry) to D4 (Exceptional Drought).
Your report shows the Drought Monitor alongside KBDI. KBDI is more responsive to recent weather; the Drought Monitor reflects the longer-term picture and is the designation most people and agencies already recognize. Both serve different purposes — neither replaces the other.
| Level | Threshold | What it means |
|---|---|---|
| Extreme | D4 – Exceptional | Exceptional drought. Rare, severe, and widespread fire and water impacts. |
| Very High | D3 – Extreme | Major impacts on water supply, agriculture, and fire conditions. |
| High | D2 – Severe | Widespread impacts. Fire risk significantly elevated. |
| Moderate | D1 – Moderate | Some water shortages. Fire risk above normal. |
| Low | D0 – Abnormally Dry / None | Near-normal or slightly dry. Fire risk not significantly elevated. |
Source: USDA Drought Monitor (droughtmonitor.unl.edu). Updated weekly by USDA, NOAA, and UNL.
Wind & Gusts
Wind speed and gust measurements at your location. The badge and severity rating are driven by peak gusts — not sustained speed — because gusts determine how far embers travel and how fast a fire spreads.
NWS Red Flag Warning criteria for most of California use gusts of 25 mph or more (combined with low humidity) as a key issuance threshold. The SPC fire weather outlook program uses 15, 20, and 30 mph as the thresholds for elevated, critical, and extremely critical fire weather conditions. Your report shows current sustained speed and tomorrow's forecast gust.
| Level | Threshold | What it means |
|---|---|---|
| Extreme | ≥ 30 mph | Extreme fire weather. Aggressive spotting and rate of spread. Extremely Critical (SPC). |
| Very High | ≥ 25 mph | NWS Red Flag Warning gust threshold for California and the western US. |
| High | ≥ 20 mph | Critical fire weather (SPC). Rapid spread possible. |
| Moderate | ≥ 15 mph | Elevated fire weather (SPC). Wind is a factor. |
| Low | < 15 mph | Below fire weather action thresholds. |
Source: Open-Meteo forecast API. Thresholds: SPC fire weather outlook criteria + NWS Instruction 10-204.
Red Flag Warning
An official NWS alert product indicating that critical fire weather conditions are imminent or already occurring. Issued when humidity, wind, and fuel moisture criteria are simultaneously met. Exact thresholds are set per NWS Weather Forecast Office region.
A Warning means conditions are present now. A Watch means conditions are expected within 12–72 hours. Your report displays these as issued by NWS — we display official products, we don't issue our own alerts.
Source: NWS Alerts API (api.weather.gov). Defined under NWS Instruction 10-204, Fire Weather Services.
Active Fires
Wildfires currently burning within 50 miles of your property, sourced from NIFC WFIGS — the authoritative federal incident reporting database used by all wildland fire agencies. Prescribed burns are excluded.
Distance is the primary severity signal. The 50-mile outer limit reflects that fires beyond this range have limited direct property threat under normal wind conditions — extreme ember cast events like Santa Ana winds are captured by the Red Flag Warning card. Note that wind direction relative to fire position is not currently factored in; an upwind fire at 40 miles can be more dangerous than a downwind fire at 15 miles.
| Level | Threshold | What it means |
|---|---|---|
| Extreme | ≤ 25 miles | Close proximity. Monitor local evacuation zones and agency bulletins. |
| Moderate | 26–50 miles | Nearby. Conditions can change rapidly with wind shifts. |
| Low | None within 50 mi | No active wildfires in the immediate area. |
Source: NIFC WFIGS ArcGIS FeatureServer. Wildfires only (IncidentTypeCategory = 'WF'). Fires ≥ 10 acres.
Fire History
Documented wildfire perimeters that have burned across your area over the past 30 years, sourced from the NIFC national historical fire perimeter database. Your report shows the top five fires by size.
Fire history reveals two things: how frequently this landscape burns, and whether fuel loads have had time to rebuild since the last major fire. Areas that haven't burned in 30+ years in historically fire-adapted landscapes often carry accumulated fuels that increase risk. Only fires of 10 acres or more are included to remove incomplete or trivial records.
Source: NIFC Interagency Fire Perimeter History (data-nifc.opendata.arcgis.com). Rolling 30-year window.
Fire Hazard Severity Zone (FHSZ)
California's statutory fire hazard designation, assigned by CAL FIRE to every parcel in the state. Three classes — Moderate, High, and Very High — defined under CA Government Code §51177 and Public Resources Code §4201–4204. California only.
FHSZ drives real consequences: CA building codes for ignition-resistant construction, vegetation management requirements, insurance carrier filings, and real estate disclosure obligations. It's a static designation updated approximately every 10 years — it reflects structural fire hazard, not current fire conditions. Properties on federal land (National Forests, BLM) are not designated and will show as unavailable.
| Level | Threshold | What it means |
|---|---|---|
| Very High | Very High | Highest risk of structure ignition. Triggers the most stringent building code requirements. |
| High | High | Significant fire threat to structures. |
| Moderate | Moderate | Elevated fire hazard. Fire could start and spread to structures. |
Source: CAL FIRE FHSZ dataset via CA State Geoportal ArcGIS MapServer. CA SRA and LRA layers.
Wildfire Hazard Potential (WHP)
A national USFS LANDFIRE classification rating the likelihood and potential intensity of wildfire at a given location, based on land cover, vegetation, fuel models, topography, and historical weather. Shown for properties outside California where FHSZ is not available.
WHP is a static landscape layer — it doesn't change day to day. Unlike FHSZ, it's not a regulatory designation; it's an informational dataset used by planners, fire managers, and researchers. Urban and developed parcels may register as Non-burnable at the parcel center — your report notes when the surrounding landscape has a different WHP class.
| Level | Threshold | What it means |
|---|---|---|
| Very High | Very High | Highest wildfire hazard. High fuel loads, dangerous terrain, or historically active fire areas. |
| High | High | Substantially elevated wildfire hazard. |
| Moderate | Moderate | Moderate wildfire potential. |
| Low | Low / Very Low | Low potential for wildfire occurrence or intensity. |
Source: USGS LANDFIRE Wildfire Hazard Potential dataset (landfire.gov). National coverage.
Fire Regime Group (FRG)
A USGS LANDFIRE classification showing how this landscape historically burned before modern fire suppression — how often and how intensely. A permanent landscape characteristic, not a current condition reading.
FRG puts your property in ecological context. Grasslands and shrublands in high-frequency, low-severity regimes naturally burned every few years; decades of suppression have allowed fuels to accumulate in these areas. Dense forests in low-frequency, high-severity regimes historically burned infrequently but intensely when they did. This context helps interpret why your other metrics may be elevated or understated relative to a simple sense of the terrain.
Source: USGS LANDFIRE Fire Regime Groups (landfire.gov). Static dataset based on pre-European settlement vegetation modeling.
Terrain
Elevation in feet and slope in degrees at your property, derived from the USGS 3D Elevation Program at roughly 10-meter resolution.
Slope is the most operationally significant terrain variable for fire behavior. The Rothermel fire spread model — the foundational model used by all US fire agencies — established that rate of spread approximately doubles every 20° of slope increase. A fire burning uphill on steep terrain can overtake running vehicles. Your report flags properties above 20° slope as a compounding risk factor when other conditions are elevated.
Source: USGS 3D Elevation Program (3DEP). Slope fire behavior basis: Rothermel (1972), USFS Research Paper INT-115.