Low pressure approaching from the North Sea is due to hit the Iberian peninsula and Balearic Islands on Thursday, bringing wind, snow and rain that will not let up before next Wednesday, national weather service AEMET reported.
The worst of the storm will be felt between Thursday and Sunday, when winds are expected to gust upwards of 100 km/h along the Cantabrian coast, in northern Spain. Strong gales will also sweep across much of the peninsula on Friday, including parts of the Mediterranean coast.
Thirty provinces in 14 regions are on alert for bad weather, including Madrid, the Basque Country, Asturias, Catalonia, Valencia, Aragón and parts of Andalusia.
Authorities are asking residents in northern and eastern Spain to remove loose items from balconies
Conditions at sea will be highly adverse in Galicia and Cantabria, where waves reaching heights of six to seven meters are forecast.
Snowfall is expected at altitudes above 900 meters on Friday, and at nearly sea level over the weekend in parts of the north.
The Canary Islands will be mostly spared, although residents can expect stronger winds and lower temperatures than usual.
Authorities are asking residents in northern and eastern Spain to remove any loose items from balconies, and warning pedestrians to stay away from trees and construction sites because of the risk of falling objects.
Drivers are also being asked to take extra care, and authorities are reminding residents of coastal areas about the dangers of walking near the sea in stormy weather.