Because of the gulf stream, the climate in Norway is noticeably warmer than what would otherwise be expected at such a high latitude. Almost half the length of Norway is north of the arctic circle. Summers can be moderately warm (up to 30 degrees C), even in northern areas, but only for limited periods. The length of the winter and amount of snow varies. In the north there is more snow and winters are dark; on the southern and western coast, winters are moderate and rainy, while further inland the temperature can fall below -25 degrees C. Some mountain areas have permanent glaciers.
In Northern Norway there is 24 hour sunshine in the summer and no sun at all at mid-winter. Although Southern Norway can not enjoy the midnight sun, at midsummer the night is very short even in Oslo - it doesn't get really dark at all.Source: Wikitravel.org