Weather in San Francisco in January

Shoulder season. January sits in between. You will get good days and you will lose some. Highs sit at 13.9 °C and the day is short; this is an indoors-with-excursions month, not an outdoors-all-day one.

January ranks 11 of 12 — near the bottom of San Francisco's year. July is the month that works, and the swing between the two is 46 points, which is a different holiday rather than a slightly better one.

Rain on 9 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at 13.9 °C the difference between a good day and a miserable one is entirely down to what you are wearing.

What the averages hide

The averages here are honest — no hidden extremes worth planning around. Across the twenty years measured, the hottest January day reached 21.5 °C and the coldest night fell to -0.3 °C, and the wettest single day dropped 67 mm — roughly 67% of the month's rain in one day.

This is the volatile part. January rainfall has ranged from 1 mm to 303 mm across the twenty years measured — a 302 mm spread around an average of 100 mm. The average is real but almost no individual January looks like it, so treat the figure as the middle of a wide range rather than a forecast.

Wind is light at 7.6 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 84%, which at 13.9 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How January sits in the year

Temperatures hold steady either side: 13.9 °C in December, 13.9 here, 14.9 in February. Nothing about the timing within the month matters much.

Daylight in January

January sits at the dark end of San Francisco's year — 9.8 hours of daylight against 14.8 at midsummer, gaining 0.6 hours across the month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

Sea temperature

The sea sits at about 12.6 °C in January — too cold to swim without a wetsuit. The sea peaks at 15.7 °C in September and bottoms out at 12.2 °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.

January in San Francisco versus nearby

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

So: January is a compromise. July is 38 points better and is what San Francisco 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 Francisco

See all twelve months in San Francisco, or where else to go in January.