Weather in San Francisco in May

Prime time. If you get to pick your dates, May is the one. Highs average 19.6 °C, lows 10.3 °C, and rain falls on 3 days — nothing in the month is working against you.

May ranks 5 of 12 in San Francisco: past the worst of the year but short of July, which is the month to book if the dates are open.

Rain falls on only 3 days, so an itinerary with no wet-weather fallback is a reasonable risk. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average May reaches 30 °C. Across the twenty years measured, the hottest May day reached 34.1 °C and the coldest night fell to 5.4 °C.

This is the volatile part. May rainfall has ranged from 0 mm to 73 mm across the twenty years measured — a 73 mm spread around an average of 18 mm. The average is real but almost no individual May looks like it, so treat the figure as the middle of a wide range rather than a forecast.

Wind is light at 9 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 78%, high enough to notice on the warm days without dominating them.

How May sits in the year

The month is on the way up: 2.2 °C warmer than April, and June adds another 2.5 °C. Late in the month feels noticeably different from the start of it, which is worth knowing if the trip is short.

Daylight in May

14.2 hours of daylight, gaining 0.9 hours across the month. That is between San Francisco's extremes of 14.8 and 9.6 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 12.5 °C in May — 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

Busy. Popular without being frantic; book the things you care about, improvise the rest.

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

May 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 — 5.3 °C warmer, the same number of rain days. San Jose is close enough to be a coin toss — 4 °C warmer, the same number of rain days.

So: May works, with July the better month by 7 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in San Francisco

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