Coastal fog and its formation: Insights for the Catalonia Coastline

Saving properties and lives are one of the premises of a weather forecaster. Coastal fog presents significant challenges not only for daily life but also for the correct functioning of infrastructures such as airports, ports, and even roads. Therefore, accurately forecasting these events is crucial. However, fog remains a relatively unpredictable meteorological phenomenon. Thus, it is essential to know the geography well and understand which types of situations are favourable to its formation and anticipate them.

In this study, various episodes from long series of spot observations along the Catalan coast have been analysed. More specifically, eight events from 2008 were chosen because they could be compared to Barcelona sounding, HRV satellite images, and buoy database. Only those which affected almost all parts of the Catalan coastline have been analysed in order to avoid a specific situation.

The conclusions show that fog events are more frequent in spring, but not exclusively. A strong subsidence inversion close to the surface is also necessary, due to the stability caused by the high-pressure system. Furthermore, the position of the anticyclone over the Mediterranean is crucial to the formation of fog. The wind path, from south to north, is determinant in acquiring humidity. Additionally, crossing from warmer to colder maritime surface temperatures helps to saturate the air mass, and also the bigger the difference between air mass temperature and sea surface temperature, the more chances there will be for its formation.

Last but not least, the more persistent the anticyclone is, the more favourable the conditions and the persistence of the event will be because the air mass acquires characteristics from the Mediterranean Sea.