A Forecast Procedure for Dry Lightning Busts

“Dry” thunderstorm (traditionally less than 2.5 mm or 0.1” of rainfall) forecasting has long been a forecast problem for the western United States. These dry thunderstorms are responsible for starting thousands of wildland fires every year. In the largest lightning outbreaks (or “busts” in the wildland fire community), hundreds of fires may be started in a 24 to 36 hour period. These extreme events put a huge strain on fire suppression efforts. Many of these fires may go unstaffed due to the lack of available fire personnel simply because of the large number of fire starts. Forecasting these events in advance, even just 24-48 hours, could help fire agencies plan resources in preparation of a large outbreak. Fires are much more likely to be controlled during the early stages, and therefore cost much less to fight.

Due to the seemingly innocuous conditions preceding dry thunderstorm development across the Great Basin, forecasting dry thunderstorm events can prove challenging and inconsistent. Jim Wallmann, an IMET at WFO Reno, recently developed WA04, a conceptual model of Great Basin dry thunderstorms that includes the pressure of the dynamic tropopause , jet streak dynamics, equivalent potential temperature, and upper level lapse rates in conjunction with the High Level Total Totals. Isentropic and satellite data analysis will be added to WA04 in the future.

This procedure was applied to several case studies of dry lightning busts including the dry lightning event in northern California on June 20-21, 2008 and the Nevada dry lightning event of August 12, 2001. It proved useful in determining the potential for dry thunderstorm development in the preceding days and hours to the initiation of the event. This presentation summarizes these case studies, and describes the WA04 procedure.