While the hydrologic cycle pays no heed to dates, hydrologists mark the start of the water year (WY) on October 1. The United States Geological Survey designates the start of the water year on this date, as it is typically in the lowest flow period of the year in the US, thus making things relatively quiet hydrologically.
WY 2015 is a good one to saying goodbye to in the Puget Sound region. A warm but normal precipitation winter resulted in incredibly low snowpack, followed by a long dry summer. Here’s the year-end water supply summary from Seattle Public Utilities. Check out the flat snowpack in the figure below and 4 months of almost no rain.