Long-Term Trends in Ice Fog Occurrence in the Fairbanks, Alaska, Region Based on Airport Observations

Ice fog typically occurs at temperatures below approximately -30 & DEG;C. Ice fog formation and persistence are affected by atmospheric processes at different spatial and temporal scales and can be influenced by anthropogenic activities that add vapor to the near-surface atmosphere. Based on meteorological observations from Fairbanks International Airport and Eielson Air Force Base (Alaska) from 1948/49 to 2021/22, we provide an overview of general ice fog climatology at the sites, changes over time, and synoptic-scale upper-level weather patterns common during ice fog occurrence. On average, ice fog occurrence has decreased by 60%-70% over the study period (median number of ice fog days at Fairbanks airport in the period 1950/51-1979/80: 16.5; median in the period 1990/91-2019/20: 6). The average lengths of ice fog events and of the ice fog season have also decreased. Trends are not linear, and rates of change vary over time. The greatest reduction in ice fog occurred during the 1970s and 1980s. Trends in ice fog hours roughly track decreasing trends in hours with cold temperatures. However, the percentage of cold hours in which ice fog occurs has decreased since approximately the 1980s. This result suggests that local changes in air pollution or near-surface moisture may also play an important role in trends in ice fog occurrence. We use self-organizing maps to assess recurring synoptic-scale weather patterns in the upper atmosphere during ice fog conditions in Fairbanks. Ice fog is typically associated with a northerly flow or low pressure gradients over the study area.SIGNIFICANCE STATEMENT: We aim to show when and how often ice fog occurs in the Fairbanks region, how this has changed over time, and what kind of larger-scale weather patterns are common during ice fog. Ice fog strongly reduces visibility and represents a hazard to aviation and other traffic. The number of ice fog hours and days per winter has decreased substantially over the 70-yr period of record. Ice fog is, on average, less persistent now than in the past. The reduction is related to fewer days with cold temperatures, but changes in air pollution and other local factors may also play an important role. Further study is needed to fully attribute the causes of the observed changes.