Those of us living in the Pacific Northwest can all attest that the winter so far has been markedly different from recent years, bringing both massive amounts of water to the region as well as mild temperatures. Our recent Special Report, “Weathering the Storm” delves into the impact of the December weather and putting it in the context of previous water years. There were both immediate and longer term effects, with warm weather leading to a large portion of the precipitation to fall as rain and immediately run off into the river system, bolstering reservoir levels and boosting PNW hydro generation to the highest levels seen in December over the past four years. The figure below plots daily average hydro output from 2024-2026 and shows the sharp increase in production in mid-December that continues to the is day, with generation sitting around 19 GW.

Figure 1 | Daily Average PNW Hydro Generation

Conditions are changing now with temperatures headed towards a slightly cooler pattern and precipitation has fallen off almost completely since Monday. The dryness is expected to continue for another week, making it the longest period of dry weather in months. However, so far hydro flows are still holding strong and should continue to show strength deeper into January and February. While precipitation is slowly down dramatically, river flows are getting a significant boost as the hydro system transitions into winter flood-risk management (FRM) operations, which require many projects to release stored water from behind the dams in order to make space in case there is an early quick melt or massive storm and lots of water shows up at the same time during the spring, to prevent flooding downstream.

Figure 2 | Daily Forebay Elevation Change by Dam (Feet)

With the release of the official January water supply forecast and January FRM requirements last week, projects are ramping up releases from storage, needing to draft significantly in order to reach end-of-month elevation targets for January, February, March, and April. The figure above plots the daily forebay elevation change at selected hydro projects, all of which have started (or continued) drafting this week, reducing their elevation each day, the stored water replacing the declining precipitation-driven flows.

Figure 3 | Total PNW Hydro Storage (MAF)

There is a lot of ground to cover; the December storms left the hydro system with significantly more water stored behind the region’s dams than is typical. The figure above plots daily storage volume for the PNW, split out between the Canadian (BC) projects, Snake River Projects, and Columbia River projects. All three regions came into January with higher storage levels than any of the past five years and are still at the head of the pack even after draw-downs in BC and the Columbia. The upshot is that the hydro system is going to continue showing strength into February and March while local demand has been mild.

We cover the rapidly changing hydro conditions with daily dashboards, regular forecasts, and timely market flash written content as part of our West Hydro Power Enterprise product offerings. Follow the link above or reach out to us at [email protected] to learn more.

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