Characterization of Lightning Occurrence in Alaska Using Various Weather Indices for Lightning Forecasting

Abstract

Alaska lost 10% of its boreal forest area due to vigorous forest fires in 2004 and 2005. Repeated lightningcaused forest fires adversely impact residents and influence earth’s atmosphere in every fire season. The authors have reported on the weather conditions of Alaska’s most severe lightning occurrence in mid June 2005. This paper examines a range of weather indices like soar, instability, ‘dry lightning’ and other factors that could clearly explain lightning characteristics in Alaska. First, lightning occurrence days from May to September were classified into ‘non or small lightning’ days and ‘lightning’ days to determine threshold values. Second, ‘lightning’ days were categorized into ‘less severe,’ ‘severe,’ ‘very severe,’ and ‘extremely severe’ to notice controlling factors on the lightning severity. Based on this analysis, the lifted index (LIFT) was selected as sensitive to assess upper air instability, and Te850 (environmental temperature at 850 hPa) was selected as sensitive to assess warm and moist air masses. Finally, the possibilities of lightning forecasts in Alaska are discussed using lightning occurrence and LIFT and Te850 in 2005. As there is a time-lag between LIFT measurements (14:00) and the lightning peak (-17:00), and around one day time-lag between Te850 and lightning occurrence, lightning forecasts using LIFT and Te850 could provide a simply applicable forecast index for Alaska.