Weather

Sunset in Oslo is about 6:00 p.m. in mid-October. See weather summaries and more resources on the Visit Norway site. The big cities will certainly be open for business, but sightseeing can be quite reduced in small towns, so you'd want to check details for your destinations.

Norway is a big country in terms of latitude and climate zones. Oslo in the south is at 60° north latitude and Nordkapp at 71° north. If you count Spitsbergen, Norway extends to over 80° north.

Western Norway is moderated by ocean temperatures of the warm North Atlantic current but wetter than the eastern mountainous sections of Norway. The NorthAmerica Atlantic current makes Norway's northern latitudes a lot warmer in winter than comparable latitudes of interior North America. A good introduction to climate is the visitnorway travel web site: http://www.visitnorway.com/us/about-norway/seasons-and-climate-in-norway/

For current weather I like the Norwegian Met website: http://www.yr.no/place/Norway/

I need to add that "best" time to visit Norway depends on what you want to do in Norway. July-August may be best for hiking, but late Feb through Easter is usually the best ski conditions.

About that moderating effect of the ocean current, here's a good example. About a year and half ago, I took a trip to Åre, Sweden in late November to catch some early season skiing. Far inland and at a high elevation, it was quite cold, never even getting close to rising above the freezing point.

Trondheim, in Norway, is about a three hour drive away from Åre, so I decided to give it a look while I was in the area. At sea level and subjected to the north Atlantic current, temperatures were around 10-15° C. As I walked around town, I had to take off the thick wool sweater I put on that morning in Sweden.

The point of the story- given the chance, I would not hestiate to visit Norway in October. Or at any time of year. There's no such thing as bad weather, only the wrong clothes and wrong activities.