St. Helena (CA) Rainfall & Precipitation: Monthly Averages and Year-Round Insights

This page shows the average amount of rainfall per month in St. Helena (CA). The numbers are calculated over a 30-year period to provide a reliable average. Let’s explore the details in depth to provide you with a complete overview.

Generally, St. Helena has a moderate amount of precipitation, averaging 800 mm of rainfall annually.

Monthly Precipitation Levels

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

The climate in St. Helena shows significant variation throughout the year. Expect 175 mm of precipitation during the wettest month December, distributed over 14 rainy days.

In contrast, August offers drier and sunnier days, with around 0 mm of rainfall over 0 rainy days.

December, the city’s wettest month, has a maximum daytime temperature of 14°C. During the driest month August you can expect a temperature of 31°C. For more detailed insights into the city’s temperatures, visit our St. Helena Temperature page.

Annual Precipitation in the United States of America

The map below shows the annual precipitation across the United States of America. You can also select the different months in case you are interested in a specific month.

Amsterdam Precipitation Compared World Wide

St. Helena’s average annual precipitation is 800 mm. Let’s compare this to some popular worldwide tourist destinations:

Athens, Greece, receives an average annual precipitation of 400 mm, making it one of the drier Mediterranean climates with rainfall mostly in winter.

In Seoul, South Korea, the average annual precipitation is 1237 mm, with most rain falling during the summer monsoon season.

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

Bangkok, Thailand, experiences a tropical monsoon climate with 1668 mm of annual rainfall, with the heaviest precipitation occurring during September and October.

How is Precipitation Measured?

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.

Global Precipitation Patterns

Tropical Rainforests: In tropical regions, rainfall is generally abundant year-round. Areas near the equator, like the Amazon rainforest, can receive up to 3000 mm of rain annually.

Desert Regions: Deserts such as the Sahara and Arabian deserts typically see less than 250 mm of rainfall annually. Rainfall tends to be infrequent, but when it does occur, it is often intense.

Temperate Zones: In temperate regions, precipitation tends to be more evenly distributed, though areas closer to the ocean may see more rain in the winter months, and areas further inland experience drier summers.

Polar Regions: Precipitation in polar regions, like Antarctica, is extremely low, often falling as snow. Average annual precipitation in Antarctica is less than 200 mm, with some areas receiving as little as 50 mm annually.

For more detailed information about St. Helena (CA)’s weather, including sunshine hours, humidity levels, and temperature data, visit our St. Helena (CA) Climate page.