San Francisco Monthly Rainfall & Precipitation

This page shows both the average monthly rainfall and the number of rainy days in San Francisco, Riviera Nayarit, Mexico. Long-term data from 1990 to 2020 was used to calculate these averages. Now, let's explore all the details to give you a full picture.

San Francisco has a notably wet climate with abundant precipitation, recording 1002 mm (39 in) of rainfall per year. It does, however, have a distinct dry season during certain months. Have a look at our detailed charts below to see how precipitation varies throughout the year.

Monthly Precipitation Levels

The average number of days each month with precipitation (> 0.2 mm (0.01 in))

The seasons in San Francisco, bring significant changes in precipitation. The wettest month, September, receives heavy rainfall, with an average of 254 mm (10 in) of precipitation. This rainfall is distributed across 18 rainy days.

In contrast, the driest month, April, experiences much less rainfall, totaling 2.4 mm (0.1 in) over a single rainy day. These distinct seasonal differences provide diverse experiences throughout the year.

September, the wettest month, has a maximum daytime temperature of 31°C (88°F). During the driest month April you can expect a temperature of 27°C (81°F). For more detailed insights into the city's temperatures, visit our San Francisco Temperature page.

San Francisco's average annual precipitation is 1002 mm (39 in). Let's compare this to some popular worldwide tourist destinations:

In Barcelona, Spain, the average annual precipitation is 644 mm (25 in), evenly distributed across the year with no extreme wet or dry seasons.

Meanwhile, Buenos Aires, Argentina, enjoys a humid subtropical climate with 1000 mm (39 in) of annual rainfall, mostly in the summer.

In Tokyo, Japan, the average annual precipitation is 1528 mm (60 in), with significant summer rains due to typhoon season.

Kuala Lumpur, Malaysia, receives 2529 mm (100 in) of annual rainfall, characteristic of its equatorial tropical rainforest climate, with consistent rainfall throughout the year and peak months during March and November.

Precipitation amounts are measured using specific gauges installed at weather stations, collecting both rain and snow and any other type of precipitation. Rainfall is measured directly in millimeters, while that from snow and ice is obtained by melting it. Automated systems often incorporate heaters to make this easier.

Information from these stations is transmitted via Wi-Fi, satellite, GPS, or telephone connections to central monitoring networks. This information is immediately updated and integrated into weather models and forecasts.

Climate change is affecting precipitation patterns worldwide, including San Francisco:

• Changing Rainfall Patterns: Global warming causes drastic changes in the patterns of rainfall. Some areas have been experiencing increased frequency and intensity of rainfall, while other areas experience longer dry spells or even droughts.
• Local Impacts: Many regions are experiencing heavier rainfall in the winter months and drier, hotter summers. This affects agriculture, water resources, and ecosystems.

• "Ginger" was the longest-lasting Atlantic tropical storm, which spun around the open ocean for 28 days in 1971.
• The world's largest snowflake was recorded in the Guinness Book of Records, at 38 cm (15 inches) wide and 20 cm (7.9 inches) thick. The snowflake fell at Fort Keogh, Montana, USA, on 28 January 1887.
• The greatest snowfall recorded was on Mt. Rainier, Washington State, USA, over 31.5 meters (103 feet) fell during the winter of 1972.

For more detailed information about San Francisco's weather, including sunshine hours, humidity levels, and temperature data, visit our San Francisco Climate page.