Until Saturday, periods of rain or showers are expected, sometimes heavy and accompanied by thunderstorms, especially on Friday, explains the Portuguese Institute of the Sea and Atmosphere (IPMA), adding that the depression will position itself at the end of Thursday to the west of the Iberian Peninsula, moving slowly to the north.

"This depression is associated with a cold front and several instability lines that will affect the weather in mainland Portugal," said IPMA in a statement.

Until Saturday, weak to moderate southerly winds are also forecast, intensifying to moderate to strong on the coast and in high areas, with gusts of up to 70 kilometres per hour (km/h) from the end of the day on Thursday, and snowfall at the highest points of Serra da Estrela.

Following the forecast of worsening weather conditions, the IPMA issued a yellow warning for the 18 districts between 12pm and 6pm on Friday due to the sometimes heavy rain accompanied by thunderstorms.

The IPMA also placed the districts of Setúbal, Lisbon, Leiria and Beja under yellow warning between 9 am and 9 pm on Thursday and Faro between 3 am and 9 pm due to the forecast of strong sea agitation, with southwest waves measuring 4 to 4.5 metres.