Andorra has two distinct seasons and two awkward gaps between them. Getting the timing right matters more here than in most destinations, because a large share of the country's businesses simply close between seasons.
Winter: December to April
The ski season normally opens in early December and runs to mid-April. Snow at the upper sectors is dependable and heavily supplemented by snowmaking. The busiest weeks by a wide margin are Christmas and New Year, the February half-term holidays in Spain and France, and Easter. January is the best combination of good snow, reasonable prices and open slopes.
Bear in mind that most visitors arrive by road over high passes. In heavy snow the Envalira pass can close, and the tunnel becomes essential. Winter tyres are legally required when conditions are signed.
Summer: late June to September
Walking season opens once the snow clears the passes, usually late June, and runs to early October. Days are warm in the valleys — often the high twenties — and cool at altitude. July and August bring French and Spanish holidaymakers and regular afternoon thunderstorms; September is the best month of the year here, with stable weather, empty paths and everything still open.
The two gaps
May and November are the months to avoid unless you have a specific reason. The lifts have stopped, the high paths are still snowbound or already freezing, and a great many hotels, mountain restaurants and attractions shut for annual maintenance and staff holidays. Prices are low because there is little to do.
Events worth planning around
8 September is Meritxell day, the national holiday, with pilgrimage to the sanctuary. The Andorra Ultra Trail in July fills accommodation across the country. Grandvalira has hosted Alpine Ski World Cup finals in March, which is spectacular but crowds the Soldeu sector. In summer the Tour de France occasionally crosses Andorran passes, closing roads for a day.
The short version
For skiing, come in January. For walking, come in September. If you are choosing between the two, September is the easier trip: no chains, no lift queues, and the mountains at their best.
Altitude and weather
Nothing in Andorra is low. The capital sits above a thousand metres and the passes go beyond 2,400, so nights are cool even in August and weather changes fast. Expect a fifteen-degree difference between the valley floor at midday and a ridge in the late afternoon, and pack a windproof layer whatever the forecast says.