You may want to add Iceland to your bucket list!

I've been inOctober (very similar to western US weather) and normal day/night - we had one snowy day, and the other two were nice, long sleeve weather. We did see (faint) northern lights but they weren't dramatic because it was so early in the season.

When we went back in May it was cold/coolish but long long days! We had a bit of rain, a bit of snow flurries and when we crossed the arctic circle, I was wearing all the clothes I brought -- being on the water was cold! We did get to see lots of puffins and other birds though so it was worth it. Outside of that day, it was long sleeves and lighter jackets.

there's no bad time to go..just like there's no bad weather -- just poor clothing choices, lol