The best time to go to Arties depends on whether you're seeking winter sports or summer outdoor adventures.
For winter sports enthusiasts, the prime season runs from December to April. During these months, the surrounding Val d'Aran mountains are typically covered in snow, offering excellent conditions for skiing, snowboarding, and other snow activities. The ski resorts in the area, such as Baqueira Beret, are usually fully operational, providing a wide range of slopes for all skill levels. You'll find the village bustling with apres-ski options and a festive atmosphere, especially around the Christmas and New Year period.
If you're more interested in hiking, cycling, and exploring the natural beauty of the Pyrenees without the snow, then the summer months, from June to September, are ideal. The weather is generally warm and sunny, great for outdoor excursions. The valleys are green, the mountain trails are accessible, and the rivers are suitable for activities like rafting. This period also sees various local festivals and events, offering a chance to experience the regional culture.
Ultimately, your choice depends on the activities you're hoping to enjoy.