The impact of snowoff timing and associated atmospheric drivers on the Alaska wildfire season
Wildfires occur each summer in the boreal forests of Alaska, with an increasing frequency of extreme fire seasons in recent decades. The wildfire season typically begins after the snow melts (i.e., snowoff) in April–May, which is trending toward earlier dates since 1959 (ranging from 2 to 4 days decade−1 over Alaska). This study evaluates snowoff dates in Alaska and related synoptic-scale atmospheric drivers in spring over 1959–2020 to assess possible linkages with the summer wildfire season. Many of the largest fire seasons followed regional snowoff dates in the earliest tercile accounting for 56%–95% of the total historical area burned by the region. Snowoff is best correlated with average daily maximum temperatures during April–May with weaker correlations thereafter. In some years, early snowoff and associated warm temperature anomalies persisted later into the summer influencing fire danger indices. This occurred in many years with the largest area burned. More limited instances of persistent lower precipitation anomalies were also found. The persistent temperature anomalies primarily occurred during El Niño conditions and the positive phase of the east Pacific/North Pacific pattern. Precipitation anomalies were most strongly associated with the Atlantic multidecadal oscillation. Blocking high pressure associated with these teleconnections was a likely driving mechanism, particularly for temperature persistence. The results indicated that the snowoff date and concurrent springtime synoptic climate conditions may provide predictability of fire weather conditions during the wildfire season when this persistence occurs. These subseasonal surface–atmosphere linkages could be used to inform wildfire-related seasonal forecasts.
Citation
Peter A Bieniek, Ph.D., Christine F. Waigl, Uma S. Bhatt, Thomas J. Ballinger, Richard T. Lader, Cecilia Borries-Strigle, Joshua Hostler, Elizabeth Fischer, Mitchell Burgard, Eric Stevens, Heidi Strader. 2025. The impact of snowoff timing and associated atmospheric drivers on the Alaska wildfire season. Earth Interactions. 29:1: DOI: https://doi.org/10.1175/EI-D-24-0001.1.