FWI: Forecasts
FWI forecast for 16 Jan 2010. Updated 16/01/10 20:54 AEDT, from the 0300 hour forecast of the 0000 UT 16/01/2010 Mesolaps analysis.
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Notes on the indices:
- The FWI (and its sub-indices: FFMC, DMC, DC, ISI and BUI) are representative of the time of maximum fire weather conditions (which usually occurs mid-afternoon).
- The Fine Fuel Moisture Code (FFMC) represents the moisture content of fine fuels and litter on the forest floor.
- The Duff Moisture Code (DMC) represents the moisture content of loosely compacted decomposing organic matter.
- The Drought Code (DC) represents the moisture content of deep compact organic matter of moderate depth.
- The ISI estimates the combined influence of wind speed and the FFMC on fire spread. It is a simple exponential function which doubles the FWI for increases in wind speed of about 20 km/h.
- The BUI is a combination of the DMC and the DC, representing the availability of the deeper or larger-sized fuel.
- The FWI is a combination of the ISI and BUI, representing the peak daily intensity of the spreading fire as the energy output rate per unit length of fire front.
- The indices are not representative of fire danger and are only indicative of fire weather conditions.
- For further inforamtion on the FWI System, a report is available for download here: Dowdy et al. (2009).
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Notes on percentiles:
- Percentiles are shown for all parameters, calculated individually for each grid point, based on 9 years of data (from the years 2000-2008).
- The percentiles provide an indication of how frequently the value of the parameter could be expected to occur at a given location. For example, if the FWI value has a percentile of 99, this suggests that FWI values as high as this would typically occur only about 3 or 4 times a year at that location.
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Notes on update times:
- Forecasts out to 2 days in advance are typically available from about 2200 AEDT.
- The forecasts are generally updated daily at about 0300, 1100, 1500, 2100 and 2200 AEDT.
- Since rainfall is not forecast, rainfall is taken to be 0 mm until observations are available (generally at about 1500 AEDT daily).
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Notes on the relationship between the FWI and the FFDI:
- The FWI shows broad similarities to the FFDI. For example, both indices are most sensitive to wind speed, then secondly to relative humidity, thirdly to temperature and finally to drought (i.e. either the Drought Factor for the FFDI or the Drought Code for the FWI).
- Some differences are apparent on a finer scale, with the FWI being relatively more sensitive to wind speed and rainfall, and less sensitive to temperature and relative humidity, than the FFDI.
- Fire Danger Ratings for FWI values are Low: 0-14, Moderate: 14-35, High: 35-64, Very High: 64-122, Extreme: 122-232 and Catastrophic 232+ (corresponding to FFDI classifications of Low: 0-5, Moderate: 5-12, High: 12-24, Very High: 24-50, Extreme: 50-100 and Catastrophic 100+), produced by matching percentiles of the FWI to percentiles of the FFDI throughout Australia.
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Notes on input data:
- NWP forecasts are used for all parameters except for rainfall which is derived from observations.
- Wind speed, relative humidity and temperature are foercast for noon Western Daylight Saving Time (i.e. 1400 Eastern Daylight Saving Time).
- Rainfall is the total for 24 hours up to 9 a.m. at the regional local time (including daylight saving). Some inland areas are permanently blank due to insufficient rainfall observations.
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