St. Helena (CA) Monthly Rainfall & Precipitation
This page shows both the average monthly rainfall and the number of rainy days in St. Helena, California, United States of America. These values are calculated using 30 years of data (1990–2020) to ensure accuracy. Now, let's explore all the details to give you a full picture.
Generally, St. Helena experiences moderate precipitation patterns, averaging 800 mm (31 in) yearly. However, this average masks significant seasonal variation, including a distinct dry season during certain months that are clearly visible in our monthly breakdown below.
Monthly Precipitation Levels
The average number of days each month with precipitation (> 0.2 mm (0.01 in))
Significant seasonal changes in precipitation occur throughout the year. During the wettest month, December receives substantial rainfall, averaging 175 mm (6.9 in) of precipitation, recorded across 14 rainy days.
In contrast, the driest month, August brings less rainfall, with 0 mm (0 in) over 0 rainy days.
December, the wettest month, has a maximum daytime temperature of 14°C (57°F). The city receives 160 hours of sunshine in this period. During the driest month August you can expect a temperature of 31°C (88°F). For more detailed insights into the city's temperatures, visit our St. Helena Temperature page.
Annual Rainfall in the United States of America: City Comparison
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.
heavy rainfall
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St. Helena vs World: Rainfall Compared
St. Helena's average annual precipitation is 800 mm (31 in). Let's compare this to some popular worldwide tourist destinations:
The climate in San Francisco, USA, is influenced by coastal weather, with 469 mm (18 in) of rainfall mostly during the winter months.
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.
Ho Chi Minh City, Vietnam, receives 1955 mm (77 in) of annual rainfall, with a pronounced wet season from May to November, typical of its tropical monsoon climate.
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.
- Mawsynram in India is noted as being the wettest place on earth, with over 11 meters (36 feet) of rain falling every year.
- In contrast, Antofagasta in Chile is among the driest places on the planet, getting less than 0.1mm (0.004 inches) per year, with some years recording virtually no rainfall.
- Nearly 1,650 thunderstorm cells are estimated over the planet at any given time.
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.
