Grassland Fire Danger Index Description

Grassland Fire Danger Index (GFDI)

The Grassland Fire Danger Index (GFDI) product is a text product containing the Grassland Fire Danger Index values that correspond to the likelihood that fires will get out of control. A 24 hour index plus a break down in 3-hourly increments over 6 days are represented in the text, giving customers a clear indication of not only the index value but also the time, duration and trends of the values on a county by county location.

The GFDI forecast can be used as a fire weather planning aid for emergency managers and various fire officials to help with decision-making on issuing burn permits, or burn bans. It may also be used for planning purposes with regard to prescribed burns. Predictive services meteorologists can use the information in resource planning. The general public may also use this product for planning purposes.

The Pleasant Hill GFDI product is issued twice per day; around 4 am and 4 pm, and is available on the Pleasant Hill WFO’s website.

The GFDI is derived from a mathematical formula that uses temperature, relative humidity, wind, and a curing term. Curing is similar to the inverse of greenness and is reported in a percentage. For example, 0 to 10 percent curing represents very green conditions, while 90 to 100 percent curing represents extremely brown and dry conditions. There are curing observers who, using a guide, will report their curing values to Pleasant Hill at least once a week.

The GFDI is highly affected by wind speed and curing values. Therefore, even on days with relative humidity values higher than 25 or 30%, the GFDI value could be in the high or very high category if the wind speeds and curing values are high enough. Because grasses are 1-hour fuels (they dry out quickly), even if there is some precipitation in the forecast is it possible that you will see higher values than you expect, i.e. if the precipitation is thunderstorms on a windy day in March or April. However, when the curing percentage is below 70%, it will be quite rare that the GFDI will be higher than the "moderate" category.