You’ve probably heard the hype about California’s "eternal spring," but if you’re actually landing at Mineta San Jose International Airport and trying to figure out if you need a parka or a tank top, looking at Fahrenheit numbers is basically like reading a different language. Most global travelers and even many locals moving in from abroad just want the straight facts on san jose weather in celsius without having to do mental math on the fly.
Honestly, the weather here is weirdly specific.
It’s a Mediterranean climate, which sounds fancy and vacation-esque, but in reality, it means we have two very distinct moods: bone-dry and sunny, or crisp and occasionally soggy. Because the city is tucked into the Santa Clara Valley, it’s shielded by the Santa Cruz Mountains to the west and the Diablo Range to the east. This creates a "rain shadow" effect. Basically, while San Francisco is getting hammered by wind and fog, San Jose is often sitting pretty in the sun.
The Annual Breakdown of San Jose Weather in Celsius
If you’re planning a trip or a move, you need to know the averages. Forget the "it's always 70 degrees" myth. It’s not.
In the peak of summer—think July and August—you’re looking at average highs of roughly 27°C to 29°C. That sounds manageable, right? But here’s the kicker: we get heatwaves. It is not uncommon for the mercury to spike to 35°C or even 38°C for a few days in a row. It’s a dry heat, though. You won’t feel like you’re walking through soup like you would in Florida, but you will definitely want an iced coffee and some shade.
Winter is a different story.
January is usually our "coldest" month. "Cold" is relative, obviously. You’re looking at daytime highs of 15°C to 16°C. That’s light jacket weather for most. But once the sun goes down, it drops fast. Nighttime lows in December and January frequently hover around 6°C to 8°C. If there’s a clear sky, it can dip down to 2°C or 3°C, and you’ll see frost on the windshields in neighborhoods like Almaden Valley or Evergreen.
Rain, Sun, and Everything In Between
Rain is almost non-existent from May to September. We get about 82% of our annual precipitation between November and March. February is statistically the wettest month, averaging around 92mm of rain. If you’re here in the winter, expect gray, drizzly days that occasionally turn into a full-on "atmospheric river" event. These are intense storms that dump a ton of water in a short window.
- Spring (March–May): This is the sweet spot. Highs range from 18°C to 22°C. Everything is green for about three weeks before the summer sun turns the hills golden (which is just a polite word for brown).
- Summer (June–August): Expect 26°C to 29°C daily. It’s incredibly consistent. You can plan an outdoor wedding in July and be 99% sure it won't rain.
- Autumn (September–November): September is actually one of the hottest months. It lingers. By November, it cools to a crisp 17°C.
- Winter (December–February): Highs of 15°C, lows of 7°C. Bring a sweater.
Why the Microclimates Matter
San Jose is huge. It’s the tenth-largest city in the U.S. by population, and its geography means the weather isn't the same in North San Jose as it is in South San Jose.
📖 Related: How to Fold a Hulken Bag: What Most People Get Wrong
Downtown and the areas near the San Jose Mineta Airport are often a bit warmer because of the "urban heat island" effect. Concrete holds onto heat. Meanwhile, if you head toward the foothills or the Almaden area, it’s often 2°C or 3°C cooler because of the elevation and the way the air settles in the valley.
The "fog line" is another thing. San Francisco’s famous fog (they call him Karl) rarely makes it all the way down to San Jose. It usually gets stuck at the gaps in the mountains. You might see a layer of gray clouds in the morning, but by 11:00 AM, the sun has usually burned through, and you’re back to that bright California sky.
Packing for the Celsius Reality
If you’re coming from a place like London or Berlin, you might see 15°C and think "shorts weather." Don't do it.
The humidity here is low, usually around 50% to 60%. This means the "feels like" temperature is pretty much exactly what the thermometer says. Without the humidity to hold the heat, the moment the sun drops behind the Santa Cruz Mountains, the temperature plummets. I’ve seen it go from a gorgeous 24°C at 4:00 PM to a shivering 12°C by 7:00 PM.
Layering is the only way to survive. You need a base layer (t-shirt), a mid-layer (hoodie or light sweater), and a shell if you're out in the winter. In the summer, just carry a light jacket if you plan on being out past sunset. Honestly, the biggest mistake people make is assuming "California" means "Malibu." San Jose is a valley city; it has its own rules.
Important Stats to Keep in Mind
- Hottest month: September (average high of 18°C is misleading; the daily high is usually 27°C).
- Coldest month: January (average high 15°C).
- Wettest month: February.
- Sunny days: Around 300 per year.
Actionable Steps for Your Visit
First, stop checking the "general" California forecast. Look specifically at the san jose weather in celsius on a localized app like Weather Underground, which uses personal weather stations (PWS) to give you data from specific neighborhoods.
If you are visiting in the winter, check the "atmospheric river" forecasts. These can cause localized flooding and mess up travel plans on the 101 or I-880 freeways. For summer visitors, always have a high-SPF sunscreen. The UV index here hits 9 or 10 frequently in July, and since it’s not humid, you won't realize you’re burning until it’s too late.
Finally, if you’re heading up into the nearby Santa Cruz Mountains for a hike or to visit a winery, subtract at least 4°C to 5°C from the valley floor temperature. The shade of the redwoods and the higher elevation change the game completely.
Stay hydrated, wear your layers, and enjoy the sun. San Jose might not have the beach, but its weather is arguably some of the most consistent and comfortable in the world if you know how to read the numbers right.