Portland (OR) Monthly Rainfall & Precipitation

This page shows both the average monthly rainfall and the number of rainy days in Portland, Oregon, United States of America. This average is based on long-term data collected between 1990 and 2020. Let's now guide you through the details for a complete overview.

Portland is known for its substantial rain/snowfall, with annual precipitation reaching 1050 mm (41 in). While the overall climate is wet, there are notable seasonal patterns that create interesting contrasts, as demonstrated in our graph below.

Monthly Precipitation Levels

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

Portland can be quite wet during December, receiving approximately 179 mm (7 in) of precipitation over 20 rainy days.

In contrast August, experiences much drier conditions, with 11 mm (0.4 in) of rainfall, spread across 3 rainy days.

December, the wettest month, has a maximum daytime temperature of 7°C (45°F). The city receives 64 hours of sunshine in this period. During the driest month August you can expect a temperature of 28°C (82°F). For more detailed insights into the city's temperatures, visit our Portland Temperature page.

Portland's average annual precipitation is 1050 mm (41 in). Let's compare this to some popular worldwide tourist destinations:

New York City, USA, receives 1276 mm (50 in) of rainfall annually, with precipitation evenly distributed throughout the year.

In Seoul, South Korea, the average annual precipitation is 1237 mm (49 in), with most rain falling during the summer monsoon season.

In Brisbane, Australia, the annual precipitation is 979 mm (39 in), making it wetter than Sydney.

Bangkok, Thailand, experiences a tropical monsoon climate with 1668 mm (66 in) of annual rainfall, with the heaviest precipitation occurring during September and October.

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.

Precipitation has a very strong role in determining the local climate and ecosystem:

• 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.

• 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 Portland (OR)'s weather, including sunshine hours, humidity levels, and temperature data, visit our Portland (OR) Climate page.