For sure, it will rain during your visit. Therefore, it is important to wear a raincoat or a waterproof jacket. It’s optional to carry an umbrella because is, usually, very windy.
It can be quite cold all year round, even during summer time. The best is to dress in layers, in order to adapt yourself to the changing weather by adding or to taking off layers at will.
It’s also better to bring a cap, gloves and scarfs.
Shoes are very important, as you will probably do a lot of walking and hiking. It is advisable to wear comfortable, waterproof hiking boots in the country side and waterproof running shoes to walk in the city.