U.S. Joint Fire Science Program


Date of this Version


Document Type



Fire Science Brief, Issue 12, September 2008


US government work.


Lightning is a natural source of wildfi re ignitions and causes a substantial portion of large wildfi res across the globe. Simple predictions of lightning activity don’t accurately determine fi re ignition potential because fuel conditions must be considered in addition to the fact that most lightning is accompanied by signifi cant rain. Fire operations managers need improved tools for prediction of widespread dry thunderstorms, which are those that occur without signifi cant rainfall reaching the ground. It is these dry storms that generate lightning most likely to result in multiple fi re ignitions, often in remote areas. In previous work the researchers developed a formula that estimates the potential for cloudto- ground lightning when dry thunderstorms are expected. This new study demonstrated the value of the formula as a predictive tool for estimating the likelihood of dry thunderstorms across much of the western U.S. This expanded utility was accomplished by integrating the formula with the predictive capacities of the Pacifi c Northwest MM5 weather forecast model. In testing during the summers of 2004 and 2005 the majority of lightning-caused fi res occurred where the predicted risk of dry thunderstorms was greater than 75%. These results indicate that this predictive tool can be very useful for identifying days when conditions are right for wildfi re outbreaks due to lightning. This forecast tool is currently available 24 hours a day for the Pacifi c Northwest region at http://www.fs.fed.us/pnw/airfi re. More work is already underway to expand coverage and improve usability, further supporting managers as they plan for the many potential fi res that can be started by lightning from dry thunderstorms.