Because of Pokémon Legends: Arceus There is a dynamic underworld, Pokémon encounters and events that can only occur when a certain condition is met. This could mean needing to complete another quest to advance an element in an area, or simply being present at a certain time of day.
There are also various weather conditions that can cause different Pokémon to appear or be a key ingredient in causing certain species to evolve while training them. Although this does mean that you are dependent on the weather when trying to complete your Pokédex to a certain extent.
Unlike the time of day, you cannot simply go through the menu and choose which weather conditions will apply to an area in Hisui. However, you can control the weather using the rest feature at Base Camp.
Once you’ve entered the area where you need specific weather conditions, head to a tent at one of the Base Camps. Then, choose any time of day you enjoy or need to be active in for your chosen job.
Every time you wake up, you can check your map to see what the weather is like in the area, based on the icon in the top right next to the area name. And, if that’s not the weather you’re looking for, just repeat the process until you get the weather you want.
You won’t notice all kinds of weather in certain areas, such as blizzards occurring in areas where there is no snow. This is the same method you’ll want to use when trying to hunt for a Full Moon, but being able to control the weather is a nice bonus.
https://dotesports.com/pokemon/news/how-to-manually-change-weather-conditions-in-pokemon-legends-arceus How to change weather conditions manually in Pokémon Legends: Arceus