This study investigates the spatiotemporal distribution of two aviation hazards associated with low-cloud-induced visibility restriction (LIMV) and snowfall (SNOW) across Iran during the 44-year period from 1979 to 2023. To conduct the research, reanalysis data were obtained from the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5) database, including low-level cloud cover, cloud base height, and snowfall precipitation. The ERA5 dataset provides a spatial resolution of 0.25° × 0.25°, 137 pressure levels, and an hourly temporal resolution. A threshold-based hazard framework was employed to identify conditions with the potential to produce the two hazards. LIMV was identified based on the simultaneous occurrence of 100% low-level cloud cover and a cloud-base height below 60 m, whereas SNOW was defined using a snowfall precipitation threshold of 0.5 mm h⁻¹. The analysis was first conducted over the Iranian landmass to characterize the regional climatological patterns and was subsequently applied to 36 selected airports to assess the occurrence of these conditions at operationally relevant locations. This research identifies the regions and times in which the likelihood of exceeding the defined visibility and snowfall thresholds is highest.

Results reveal distinct spatial and seasonal characteristics for the two hazards. LIMV occurs predominantly during autumn and winter and is concentrated in the northern half of Iran, particularly along the southern coast of the Caspian Sea, in Ardabil, and across northwestern Iran. In contrast, SNOW is largely confined to winter and is primarily concentrated over mountainous and high-elevation regions, particularly the Alborz and Zagros ranges and northwestern and western Iran. At the airport scale, Ardabil experiences the highest combined annual hazard occurrence, with an average of 569 h yr⁻¹, including approximately 367 h associated with LIMV and 202 h associated with SNOW. In contrast, the selected southern airports, including Kish, Bushehr, and Bandar Abbas, experience very limited snowfall-related hazard conditions, while LIMV hours are also substantially lower than those observed at airports in northern and mountainous regions.

The long-term trend analysis indicates a predominantly significant decline in the annual hours associated with both LIMV and SNOW across a substantial part of Iran during 1979–2023. The strongest decreases in LIMV occur mainly across northern and western Iran, whereas the largest declines in SNOW are concentrated over mountainous areas of the Alborz and Zagros ranges. In contrast, weaker or near-zero changes are observed across parts of central, eastern, and southeastern Iran, indicating considerable spatial heterogeneity in the long-term evolution of these hazards.

Overall, the results demonstrate that the climatological occurrence and long-term changes of LIMV and SNOW are strongly dependent on the geographic and climatic characteristics of different regions of Iran. The findings should, however, be interpreted as representing the climatological likelihood or potential occurrence of threshold-defined hazardous conditions rather than direct observations of operational visibility or airport disruptions. Because ERA5 reanalysis may have limitations in representing localized atmospheric processes and airport-scale conditions, future studies should complement the present large-scale climatological assessment with ground-based observations, airport operational data, and higher-resolution modeling approaches to improve the assessment of aviation-related weather risks.