Intercomparison Between METAR- and SYNOP-Based Fog Climatologies

Abstract

Weather observations and forecasts play a crucial role in the safety and economics of aviation, particularly in the presence of hazards such as fog. Climatological studies of this phenomenon are hence standard information for the aviation industry. Some aeronautical meteorological stations located at airports are also combined with synoptic stations and have to provide local and current weather conditions in two different types of reports: SYNOP for synoptic purposes and METAR for aeronautical purposes. When climatological studies are to be carried out, the question arises of which type of report is more appropriate for the task. In this work, a comparison is made between these two types of hourly meteorological observation reports, 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 diverse databases. A perfect agreement between the two reports is not found, but a varying degree of similarity depends on the variable. 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 climatology. In conclusion, SYNOP data could be used instead of METAR in statistical studies if the need arises, but with the caveat that fog frequency of occurrence should not be interpreted too strictly.