We all remember the epic snow storm from last February, but as a new water year begins, we look back on the precipitation and snowpack received in our region to see how we fared overall. Then we take a peek ahead at what we might expect in the coming water year.
The water year is defined by the U.S. Geological Survey as the 12-month period beginning October 1, for any given year through September 30, of the following year. It is used by scientists, government agencies, and water managers because it aligns with the natural cycle of snow accumulation in winter and runoff and use in spring and summer, ensuring annual precipitation measurements reflect the complete cycle before the new year begins.
Last fall we began our discussion of the past water year with a forecast of a coming La Niña. La Niña is one of three phases of the El Niño Southern Oscillation (ENSO), characterized by periodic changes in the water temperature and wind direction in the Pacific Ocean. La Niña years often bring cooler than average sea surface temperatures while El Niño years are the opposite. (For more information about this normal weather pattern disruptor, click here or here.)
During a La Niña, the Pacific Northwest often experiences cooler temperatures and greater precipitation.
While threatening to make an appearance, last year La Niña did not arrive. However, some effects of the trend were experienced. There were cooler temperatures and more rainfall in our region than we experienced during the previous several years. The end result was more water in our local reservoirs at the end of the irrigation season than we have experienced for some time.
Our region receives over 70% of our annual precipitation between October and March. During this last water year, four of the five months when we received greater than normal rainfall fell in this time period. These were the months of November, December, February and March. We concluded the water year with one more month of greater than normal rainfall in September. Despite this apparent abundance our total precipitation was only 17.68 inches, falling 1.83 inches below a norm of 19.51 inches experienced over the last 25 years.
The winter accumulation of snowpack in our mountainous region was significant and carried us through our typically dry summer season, and there is reason to be hopeful about the coming water year. The El Nino Diagnostic Discussion issued by the National Weather Service Climate Prediction Center reports that La Niña conditions are present and favored to persist through December 2025 – February 2026, with a transition to ENSO-neutral likely in January-March 2026 (55% chance).
While total precipitation is important, snowpack is the key to a sufficient water supply for all water users, municipal, industrial and agricultural. Check out the new Snowpack section of our Water Report page where we will post snowpack updates through the coming winter months.