Riverside’s climate is classified as semi-arid (BSh) with a tendency toward an arid climate (BWh), characterized by hot, dry summers and mild, relatively wet winters. Average monthly temperatures range from 54.8°F (12.7°C) in December to 79.8°F (26.6°C) in August, though extreme temperatures have been recorded, including a high of 118°F (47.8°C) on July 6, 2018, and a low of 18°F (-7.8°C) on January 15, 1911.

Riverside receives an average of 9.39 inches (239 mm) of precipitation annually, with most rainfall occurring between November and April. February is typically the wettest month. The wettest recorded year was from July 1940 to June 1941, with 22.72 inches (577.1 mm) of rainfall, while the driest year, from July 1960 to June 1961, saw only 2.79 inches (70.9 mm) of precipitation.

Despite its pleasant winter conditions, Riverside has long struggled with air quality issues. The city has been ranked among the most polluted regions in the U.S., with high levels of year-round particle pollution. In 2003, a study by the National Campaign Against Dirty Air Power identified the Riverside-San Bernardino-Ontario area as one of the nation’s most polluted regions. The American Lung Association also rated Riverside County among the worst counties for smog in 2020.

Much of Riverside’s smog is due to prevailing wind patterns that carry pollution from the Los Angeles Basin, the Port of Los Angeles, and the Port of Long Beach into the Inland Empire. Additionally, emissions from Southern California’s heavy traffic contribute to the issue. However, significant efforts have been made to reduce pollution, including the introduction of Metrolink mass transit, and converting the city’s bus fleet to natural gas. These measures, along with regulations set by the South Coast Air Quality Management District, have helped improve air quality over the years.

As Riverside continues to grow, the city remains committed to balancing development with sustainability, working to mitigate environmental challenges while maintaining its unique climate and natural beauty.