While for most the fast-approaching date of September 30^th means the end of the summer or the end of the 3^rd quarter of the year, for those in the know it marks the end of 2025.  For the Pacific Northwest hydro system, the calendar operates based on the water year, which begins on October 1^st and lasts until September 30^th.  So we are currently less than two weeks away from the end of the 2025 water year and the transition to 2026.  With that in mind, attention is starting to turn to the coming fall and the new water year and how things are likely to play out.

There has been some excitement this week, starting with a change in the STP streamflow forecast moving a significant volume of water out of October and into September.  Total system hydro generation saw a sizeable uptick Tuesday when generation jumped up to 9.9 GW for the heavy load block from barely 6.7 GW just two days prior on Sunday.  The changes are giving some life to what has been lackluster output for much of the summer.

Figure 1 | Total System HL PNW Hydro Generation

Overall hydro storage is in a strong position heading into the new water year, especially when it comes to Canada.  Current storage volume between Mica, Arrow, and Duncan dams in BC is 16.3 MAF (see the figure below, taken from our PNW Hydro Elevations interactive tool), which is higher than three of the past four years (only 2022 was higher with a total volume of 17 MAF).  By comparison, at this time last year Canadian storage was 2.5 MAF lower. 

Figure 2 | Daily Total Hydro Storage (MAF)

The extra water will be a help given the dry stretch that has been in place in the PNW in recent years and the early indications calling for a drier than normal water year once again in 2026.  This has been a consistent pattern in recent years; four our of the past five water years have resulted in Jan-Jul runoff coming in less than 80% of average.  Just as with storage, 2022 was the sole exception with 105.8 MAF (102% of normal).

In the much-too-early water supply forecasts coming from the Northwest River Forecast Center for Jan-Jul 2026, the current projection shows Jan-Jul total volume at 93 MAF, or 90% of normal.  Forecasts around this level have become the norm in recent years as during the past four years the water supply forecast (ESP10) at the start of October has come in between 90 MAF and 97 MAF.  The figure below plots the daily forecast number for each water year and illustrates how much volatility there is throughout the year.  The two periods of greatest volatility are Q4 (especially November and December) and then during spring melt and runoff in March (although 2022 is an exception with only a surge of very late spring atmospheric river weather patterns inundating the West with precipitation and saving the PNW from another dry water year).  Still, watching how the water supply forecast evolves during November and December will be some of the first early indicators of how the heart of the water year will play out come January.

Figure 3 | ESP10 Jan-Jul Water Supply Forecast for The Dalles, Past 4 Year (MAF) 

With the new water year right around the corner, now is the perfect time to learn more about the Energy GPS Enterprise package focusing on West Hydro for both the PNW and California.  Follow the link or email us at [email protected] to learn more.