According to a statement from the Portuguese Institute of the Sea and Atmosphere (IPMA), these four districts are already under yellow warning due to fog with “persistence for more than 48 hours, especially in valley areas”.

From 00:00 on Saturday and until 12:00 on Sunday, the alert changes to orange for these districts, due to “fog, which can be freezing, persisting for more than 72 hours, especially in valley areas”.