Summarizing the posts about the ideal seasons for travel; I’ve only been to these places, and here’s the information!
Germany: Cologne, Dusseldorf
Not suitable for early October; it tends to be overcast with continuous rain.
France: Paris
I’ve been twice, in late April and mid-September. The weather wasn’t great, but since Paris is primarily known for its museums, the limited outdoor activities didn’t affect the experience.
Netherlands: Amsterdam and The Hague
The weather in November and around Easter (April) isn’t favorable. Personally, I think the best time to visit the Netherlands is in August and September.
Norway: Tromsø
I went in early February, and the weather wasn’t good. My friend went in early March, and the weather was excellent. Based on recent posts, November’s weather also seems fine.
Italy
I declare that March is a fantastic time to visit Italy! The weather is very pleasant, with temperatures in the teens, and there isn’t much rain. However, Easter (April) is already quite hot, and the queues are exceptionally long.
Austria: Vienna
Czech Republic: Prague
Hungary: Budapest
Not recommended to visit in December during Christmas; the weather is not good.
Switzerland: Zermatt, Interlaken, Lucerne, and Zurich
I might have been lucky; I went at the end of May, and every day was sunny. Generally, the most suitable times are July, August, September, and during the snow season.
United Kingdom: London
August in the gloomy empire isn’t ideal either. Just go with the flow and dress warmly.
Spain: Barcelona, Madrid, Seville
Portugal: Lisbon
The weather in mid-September is particularly suitable, with summer temperatures but not too hot.