La Laguna's altitude — about 550 metres — gives it a noticeably cooler and greener climate than the Tenerife coast. It can be genuinely cold in winter, with mist and rain, and pleasantly mild in summer when the coast bakes. If you dislike the heat of a coastal Canary Islands summer, La Laguna is a good base.
The best time to visit is spring (March to May) or autumn (September to November), when the weather is mild and the city is not at its fullest. The Romería del Santísimo Cristo on 13-14 September is the most important festival, drawing pilgrims from across the islands and transforming the historic centre. Carnival in February is celebrated island-wide but La Laguna has its own events. The university year (October to June) keeps the city active.
Year-round the climate is comfortable enough for exploring the city; the Anaga park above is most reliably clear of cloud in summer.