Monday, 17 November 2003: 4:00 PM
Forecasting dry lightning in the western United States
Dry lightning events often lead to large wildfire outbreaks in the forested regions of the western US. In previous studies, we have shown the utility of a simple index to estimate the risk of “dry” lightning strikes (those that occur without significant accompanying rainfall) in the Pacific Northwest. Using upper-air data from Spokane, WA, the temperature difference between 850 hPa and 500 hPa and the dewpoint depression at 850 hPa were found to be useful indicators for estimating the risk of dry convection. In the current study we are expanding the use of this index to the entire western US. Because large regions of the mountainous west are above the 850 hPa level, the index has been modified to use inputs from the 700 hPa level. In order to forecast the risk of dry convection, output from the MM5 mesoscale model was also used to compute the index. The methodology for distributing the index from point locations to gridded model fields will be presented. Results of forecast dry lightning risk using constant-pressure surfaces and model sigma-levels will be compared. Forecast risk will also be compared with actual fire locations.