San Jose Weather & Climate: The Ultimate Year-Round Guide

Typical Weather Patterns

San Jose, located in the heart of the Santa Clara Valley, is characterized by a mild Mediterranean climate. This yields a landscape defined by two primary seasons: a long, dry, warm summer and a short, cool, moist winter. Because it is inland and sheltered by mountains, San Jose is notably warmer and drier than its neighbor, San Francisco. The city averages nearly 300 days of sunshine annually, creating a reliable consistency that locals often take for granted.

Daily Climate Behavior

In San Jose, the weather follows a predictable rhythm, particularly in the warmer months:

• Morning: The day often starts with clear skies or a light "marine layer" (low-lying stratus clouds) that creeps in from the San Francisco Bay. This keeps early hours crisp but melts away by late morning.
• Afternoon: This is the warmest part of the day, with temperatures peaking between 2:00 PM and 4:00 PM. Around 4:00 PM, a cooling "delta breeze" or sea breeze typically pulls through the valley from the northwest, keeping humidity low and comfort high.
• Evening: Temperatures drop rapidly after sunset. Even on the hottest summer days, the lack of humidity allows for significant "radiational cooling," meaning evenings are almost always cool and require light layers.

Seasonal Trends

Spring (March – May)

Often considered the most beautiful time in the valley, spring brings the tail end of the rains and the sudden greening of the surrounding foothills. Temperatures are mild, typically ranging from 55°F to 70°F (13°C–21°C). This is a transitional period where wildflowers bloom before the summer aridity sets in.

Summer (June – August)

Summers are bone-dry; it is rare to see any measurable rainfall during these months. Highs typically hover in the low 80s°F (28°C), though occasional heatwaves can push temperatures into the 90s or even triple digits. However, the lack of humidity prevents the weather from feeling oppressive.

Autumn (September – November)

September and October often host "Indian Summers," where temperatures remain warm or even peak for the year. By November, the first significant rainstorms arrive, and the landscape begins to transition from golden brown back to green.

Winter (December – February)

Winters are cool and wet, though "wet" is relative; the city only receives about 15 inches of rain annually. Daytime highs stay around 60°F (15°C), while nighttime lows rarely dip to freezing. Frost is possible in the more rural outskirts but uncommon in the urban core.

Microclimates and Regional Variations

San Jose is a textbook example of microclimate diversity due to its geography:

• The Rain Shadow Effect: The Santa Cruz Mountains to the west act as a barrier, forcing clouds to dump rain on the coast (Santa Cruz) while leaving San Jose significantly drier.
• North vs. South: Northern San Jose, closer to the San Francisco Bay, is cooler and breezier. As you move south toward Almaden or Morgan Hill, the marine influence fades, and temperatures in the summer can be 5–10°F higher.
• The Foothills: Areas like the Diablo Range to the east experience sharper temperature swings, with hotter days and colder nights than the valley floor.

Historical Context & Unique Phenomena

• Rare Snow: Snow in downtown San Jose is a generational event. Significant accumulations occurred in 1976 and 1962, but usually, snowfall is restricted to the peaks of Mount Hamilton, which turns white and serves as a backdrop for the city during cold winter stabs.
• The Santa Ana-Like Winds: Occasionally, high pressure over the Great Basin causes "offshore flow," where warm air is compressed as it descends the Diablo Range. This triggers sudden spikes in temperature and fire weather conditions, primarily in the fall.

How Locals Experience the Weather

Locals refer to their climate as the "Eternal Spring." Because the air is dry, the shade provides immediate relief from the sun, and the evening breeze is a central part of the lifestyle, often dictating outdoor dining and social habits. There is a cultural understanding that regardless of the daytime high, it will be cool by sunset, leading to a ubiquitous habit of carrying a light jacket even on sunny days. The weather is rarely an obstacle to outdoor activities, making cycling, hiking, and patio culture year-round staples.