Annual Average Rainy Days

Riverside receives an average of about 15 days of rain per year. This is relatively low compared to other inland cities in California. Rainfall is mainly concentrated in the winter and early spring, with very little rain during the summer. However, sudden downpours can occur during El Niño events or monsoon seasons.

Monthly Average Rainfall

The monthly average rainfall in Riverside varies greatly depending on the season and monsoon influence. The average rainfall for each month is as follows:

Riverside

• January: about 3.0 inches
• February: about 3.5 inches
• March: about 2.8 inches
• April: about 1.5 inches
• May: about 0.7 inches
• June: about 0.3 inches
• July: about 0.0 inches
• August: about 0.1 inches
• September: about 0.2 inches
• October: about 1.0 inches
• November: about 2.0 inches
• December: about 2.9 inches

Main Features:

• Winter (December to February): This is the period with the most rainfall, and frequent thunderstorms can occur due to monsoon influence.
• Spring (March to May): Rainfall gradually decreases in spring, leading to dry weather. However, strong thunderstorms can occur in March due to monsoon influence.
• Summer (June to August): Very dry, with short and intense downpours occurring rarely during the monsoon season.
• Autumn (September to November): Rainfall increases again in autumn, especially in October and November, when monsoon influence can lead to higher precipitation.

Record Rainfall

Record Rainfall: The highest recorded rainfall in Riverside occurred during a storm in January 2005, with 6.5 inches (about 165mm) of rain. This amount of rainfall resulted in severe flooding and inundation in the area.