Weather in San Jose in December

Shoulder season. December sits in between. You will get good days and you will lose some. Highs average 15.2 °C, lows 5.6 °C, and rain falls on 11 days — nothing in the month is working against you.

December ranks 12 of 12 — near the bottom of San Jose's year. May is the month that works, and the swing between the two is 34 points, which is a different holiday rather than a slightly better one.

Rain on 11 days, 4 of them heavy. Enough to need a plan B, not enough to need a plan around it. Pack for 15.2 °C days and 5.6 °C nights; the spread matters more here than any single number.

What the averages hide

The averages here are honest — no hidden extremes worth planning around. Across the twenty years measured, the hottest December day reached 22.4 °C and the coldest night fell to -3.4 °C, and the wettest single day dropped 89 mm — roughly 78% of the month's rain in one day.

December is moderately variable: 3 mm in the driest year against 255 mm in the wettest, around an average of 114 mm. Roughly two Decembers in three land near that average, and the third does something else entirely.

Wind is light at 6.5 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 81%, high enough to notice on the warm days without dominating them.

How December sits in the year

Temperatures hold steady either side: 20.1 °C in November, 15.2 here, 15.4 in January. Nothing about the timing within the month matters much. Rain has already shifted: 5 days more than November had.

Daylight in December

December sits at the dark end of San Jose's year — 9.6 hours of daylight against 14.7 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

Sea temperature

The sea sits at about 13.3 °C in December — too cold to swim without a wetsuit. The sea peaks at 15.4 °C in September and bottoms out at 12.3 °C — water lags the air by a month or two, which is why the best swimming often comes after the best weather.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

December in San Jose versus nearby

If San Jose is one option among several, the nearby comparison is worth making. San Francisco is close enough to be a coin toss — within a degree on temperature, 1 day more rain. Napa is close enough to be a coin toss — within a degree on temperature, 1 day more rain.

So: December is a compromise. May is 34 points better and is what San Jose is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in San Jose

See all twelve months in San Jose, or where else to go in December.