Intercomparison Between METAR- and SYNOP-Based Fog Climatologies

Weather observations and forecasts are crucial for aviation safety and efficiency, particularly in the presence of hazards such as fog. Hence, climatological studies of this phenomenon are standard information for the aviation industry. Aeronautical stations combined with synoptic stations have to provide local and current weather conditions in two different types of reports by using the same instrumentation: SYNOP for synoptic purposes and METAR for aeronautical purposes. When climatological studies have to be carried out, the question of which type of report is more appropriate for the task arises. In this work, a comparison between these two types of hourly meteorological observation reports is made, with the aim of identifying the conditions under which differences can have a significant impact on the final results. For this purpose, SYNOP and METAR reports for the period 2000–2019 from 13 Argentine airports were selected from different databases. Results show that level of agreement depends strongly on the variable of interest. A key difference is found in “present weather” mainly due to different reporting rules. In this context, six different selection criteria using visibility, dew point depression, and present weather are used to evaluate the impact of the differences found in the fog and mist climatology. In conclusion, SYNOP data could be used instead of METAR in statistical studies if the need arises, but with the caveat that the frequency of fog occurrence should not be interpreted too strictly.