When to go — California

Optimal period for California is April-June (spring) and September-October (autumn). Perfect weather across the territory (LA 22-26°C, SF 17-22°C, San Diego 22-25°C), accessible Yosemite and Sequoia, full Yosemite waterfalls April-June (Sierra snowmelt), open Big Sur Route 1 (sometimes closed in winter from landslides), Napa vineyards foliage in September-October, reasonable airfare (Paris-LA €700-1,000 return).

Summer (July-August) is the peak season for accessible Western parks (Yosemite, Sequoia, Lassen, Lake Tahoe — roads open), but extreme heat in interior valleys (Sacramento, Bakersfield 35-40°C, Death Valley 50°C), serious wildfire risk (Aug-Oct, 2018/2020/2023 episodes affected SF and Yosemite), peak airfare (€1,000-1,500 return), massive crowds (Yosemite, Disneyland, Universal Studios saturated). Paradox: cool San Francisco in summer (fog June-July, 15-20°C, June Gloom) — bring fleece even in July.

Winter (November-March) is the season only for Southern California — LA, San Diego, Palm Springs at 18-22°C, blue sky, gray whale watching offshore (Dec-April, $40-80 excursions), Tahoe and Mammoth Mountain in full ski season. Yosemite and Sequoia largely closed (Tioga Pass cut Nov-May, Glacier Point cut, Yosemite Valley limited). Seasonal rain Northern California (SF, Napa, Mendocino: Dec-March rains). Sometimes closed Big Sur Route 1 (landslides). Cool coastal waters (sea 12-15°C, wetsuit surfing mandatory). Stratospheric Christmas/New Year fares.

Events to note: Coachella Festival (Indio, near Palm Springs, two April weekends, one of the world's largest music festivals), Rose Bowl (Pasadena, January 1, parade and football game), Outside Lands (San Francisco, August, Golden Gate Park music festival), San Francisco Pride (June, largest in US), Comic-Con San Diego (July, major pop culture convention).