What to look for
Fully waterproof, not water-resistant, with taped seams and zips down the sides so they go on over boots. Light, packable ones live in your daypack until the weather turns, which it will.
Rain pants or snow pants?
For most winter trips, waterproof over-trousers on top of thermal leggings beat insulated ski trousers: more versatile, and you can peel a layer in a warm car. Snowmobile and many winter tours hand out overalls.
The wet side of the country
The south and southeast catch the Atlantic lows first: Vík gets 1730 mm a year against Reykjavík's 876 mm. The north and east, in the mountains' rain shadow, are far drier — Akureyri gets 573 mm and Mývatn 464 mm.