Scandinavia

If you want fewer crowds but decent weather, early fall. We visited Denmark and Norway in September/October 2023. Too late for the beaches south of Copenhagen, and too early for cross-country skiing in Norway, but great for sightseeing in both countries. Oh, it did rain some of the time.

The quick, short and to the point recommendation would be something like May - September. But of course the world is much more nuanced than that. The big question is where you want to go and what kind of trip you want to have.

Popular cities, locations and attractions: You can feel the crowds in (mainly) July and August, but we're not plagued by overtourism to the same extent as you'll see in e.g. Venice and Amsterdam.

Rural communities, small islands, etc.: Some places have their tourism infrastructure shut down during the low season.

Scandinavia also cover a really large area. So obviously weather and (depending on the season) sunlight hours can vary drastically depending on where you go.

Trains run all year round, if that was your concern.

Define "best".

Trains are running all year through and are more busy during summer months, because most people travel then.

It seems you live in Arizona, which means it's safe to assume you like it hot. Any time from FEB 15 to OCT 15 is the best time to visit Scandinavia. The last possible day for swimming is on SEP 24, our Indian summer. The day after autumn will hit. March is an underappreciated month. The light starts flooding our senses and icicles start melting.

I would be cautious with such date related statements for whole Scandinavia because the area is so huge. While the statements might be valid for Gothenborg the situation in Norway's Tromsø or Denmark's Rømø can be very different.

An example from my side: end of May 2023 we had heavy snow falls with under 0° C in Tromsø while I had around 30° C in Oslo end of May 2018.

MarkK; You are right to mention those regional Scandinavian differences in temperature, and I could have been more explicit, solely referring here to Göteborg, Malmö and therefore also the entirety of Danmark, as these three share the same weather patterns, even though 2018 was the least representative year there has been over the last half-century as far as temperatures are concerned, since if memory serves that was the year of the heatwave and the double length summer, starting i April.

And now that I think about it some more... and read some more comments, I realize I can be, and perhaps should be, even more specific and explicit, as every word was meant to be taken literally. Over the last half-decade I have been present in Malmö the day the summer actually ended, (five years, every year) for the late season swimming. Proper Scandinavian summer, nothing less, with the expected attendant temperatures. The sea takes a good long while longer to cool off, as it can't even start to do so until the summery weather eventually yields, which means it is still summertime underneath the waves too. When is the last chance for a swim in North America? That could depend on whether you are in Seattle or Orlando. The last chance for a regular swim within Scandinavia really is on or around SEP 24. Is it a miracle? Who knows. But first hand experience means that it can be stated as fact!

I went in early June, not too busy. In Norway not everything is open till end of June.

For May-July bring eyeshades for sleeping, since even well below the Arctic Circle it stays light all night.

Saying that the last possible day of swimming is a certain date has very little to do with reality. Even if you limit the area and state that it only applies to the Swedish west coast and the entire Denmark. They might share the same large scale weather patterns, but there are so many regional and local differences within the area that affect things like water temperature. And there are also variations from year to year, some years September will be warm, other years autumn will come earlier and September will be chillier.

Not to mention that if it's possible to swim or not is very much a matter of personal preference, some people won't even consider going in the water if it's less than 25°, others think that as long as the water is not covered by ice nothing will stop them from taking a swim.

And now that I think about it some more... and read some more
comments, I realize I can be, and perhaps should be, even more
specific and explicit, as every word was meant to be taken literally.
Over the last half-decade I have been present in Malmö the day the
summer actually ended, (five years, every year) for the late season
swimming. Proper Scandinavian summer, nothing less, with the expected
attendant temperatures. The sea takes a good long while longer to cool
off, as it can't even start to do so until the summery weather
eventually yields, which means it is still summertime underneath the
waves too. When is the last chance for a swim in North America? That
could depend on whether you are in Seattle or Orlando. The last chance
for a regular swim within Scandinavia really is on or around SEP 24.
Is it a miracle? Who knows. But first hand experience means that it
can be stated as fact!

I know you like exaggerations and flamboyant language, but five anecdotes is not enough to make such broad statements. Especially since the actual weather data doesn't support the your statement.

Maximum air temperature in Malmö in September:

24th 25th
2020 19.6° 16.7°
2021 16.1° 18.3°
2022 17.9° 17.7°
2023 18.2° 18.3°
2024 18.5° 16.4°

So yes, last year the 25th was colder than the 24th, and the same in 2020. But in 2021, the 25th was actually warmer than the 24th. And in 2022 and 2023 the temperature was roughly the same. So it varies a lot from year to year, and also depending on where you are.