Tenerife's climate is famously stable: the Canaries sit at 28 degrees north in the Atlantic, with trade winds keeping temperatures mild year-round. The south of the island is almost always sunny; the north is cloudier and greener. Average temperatures range from 17°C in winter to 24°C in summer, making it a viable year-round destination.
For the mountains and the interior, spring (March to May) and autumn (October and November) are best — Teide can be snow-covered in winter, and hiking is more comfortable before the summer heat builds. The hiking season in the Anaga and Teno mountains is year-round, but spring brings wildflowers and cooler walking conditions.
The main peak season for northern European visitors is November through April, when escaping grey skies at home is the main motivation. July and August are crowded in the south. Carnival in Santa Cruz, usually in February, is the island's biggest event and worth timing a visit around — but book accommodation well in advance.