April 1 is the most important day for evaluating California’s water resources for the year and is considered the end of the rainy season, which runs from Oct. 1 through March 31. The last day of March is also when final snowpack measurements are made in the Sierra. The bad news this year is that the snow is already almost gone. On average, California’s April 1 snowpack stores around 27 inches of water, equivalent to billions of gallons of water.