When is the best time to visit Norway - especially its waterfalls?
I'd say the best time (especially for waterfalling) is somewhere in late June and early July. It is during this time that you'll get peak snowmelts from winter accumulations and a reasonable chance of decent weather (though it can rain year round especially around the fjords). Moreover, you can take advantage of the longest days of the year, and as you get above the Arctic Circle (in the northern parts of Nordland county and above), you'll experience the midnight sun. Depending on the snowpack, hiking becomes more feasible and temperatures are more comfortable.
As for the rest of the year, here's what you have to look forward to...
In Autumn (late September through early December), you can experience fall foliage. The length of daylight quickly transitions towards longer nights, and the temperatures get cooler. Storms start bringing snow and a lot of the highland passes close. At least the tourist crowds dwindle and it's a chance for visitors to see a side of Norway few outside of locals get to see.
In Winter (late December through early March), people flock to the slopes. Even with the polar nights in the north and nearly 20-hour nights in the southern parts of the country, skiing is a big deal (even under the lights). It's probably not a good time to go waterfalling though some daredevils use the arctic cold conditions (usually below freezing in most of the country) to go ice climbing on waterfalls themselves!
In Spring (late March through early June), the cold grip locking the waters in ice and snow start to relinquish. Weather can be unpredictable but daylight hours get longer (midnight sun starts to occur above the Arctic Circle in late May), flowers start to bloom, apples ripen, waterfalls start to boom, and hiking becomes feasible. Waterfalling in this season can be rewarding as it's still shoulder season, but not all mountain roads have opened yet. If skiing's your thing, there's bound to be plenty of slopes still full of snow (in fact, you can even ski in summer).
Have A Great Story Or Comment You'd Like To Share?
Here's your chance to share them (as well as post a picture)!