Recent Anomalous Lightning Occurrences in Alaska - the Case of June 2005 -

Abstract

Lightning occurred in Alaska an extraordinary number of times 120,000 a year, or 4 times more than average in 2004, 2005, and 2007, starting 500 forest and wild fires. Given the rainless conditions at the time, fires in 2004 and 2005 burned 10% of Alaska’s forests. In 2007, however, fires were suppressed by rainy weather. To determine the causes of such unusual activity, we analyzed cloud-to-ground (CG) lightning data for the last 22 years, since 1986, radiosonde data measured at Fairbanks, weather maps from various heights, and satellite images. This comprehensive analysis of thunderstorm activity clearly showed weather conditions during the disastrous lightning season of 2005. Yearly, monthly, and daily lightning trends and conditions surrounding ordinary cell thunderstorm formation over Alaska are discussed. Conditions related to the exceptionally large number of occurrences on June 15, 2005, were clarified based on 11 days of weather maps and emagrams and considering a wide variety of weather conditions. The most anomalous lightning conditions occurred when center of thermal low and 500 hPa persistent high was in close proximity over Alaska.