The Pacific Northwest has enjoyed a mild fall so far.  Notwithstanding some coolness for the holiday weekend and this week so far, looking at average daily HDDs in November compared to previous years (shown in the figure below), we see an average of 16.8, the lowest (warmest) month of November going back to 2017.  The mild temperatures are expected to continue moving forward deeper into December. The bottom pane of the column shows projected daily average HDDs through the first 15 days of the month in 2025, compared to historical values for the 1^st half of December.  At 20.1, HDDs this December are expected to come in lower than every year except for 2023 and nearly 5 degrees warmer than last year.

Figure 1 | PNW Average Daily Heating Degree-Days by Year 

We can see the change coming in the temperature forecast for the Pacific Northwest (the 15-day outlook shown below, courtesy of Atmospheric-G2).  There is a marked uptick in temperatures on the way starting tomorrow and lasting up to next weekend (and beyond in the eastern portions of the PNW) that should push daily highs up above 50 degrees and put the Portland overnight lows at nearly 50 degrees. 

Figure 2 | Atmospheric G2 NWPP Temperature Forecast 

The warmth is significant for a couple of reasons.  Not only is it keeping load numbers mild—during a time when so much focus is on structural load growth, mild weather can disguise or dampen the effects of structural changes—but it is also impacting the build-up of snow heading into the winter.  This is important as snowpack is a crucial determinant of water supply for the hydro system come spring and summer time.  The 2026 water supply forecast has seen a recent uptick over the past several days but there is not escaping the fact that snow levels are off to a very poor start this water year.  The figure below shows Columbia daily snow water equivalent (in inches) this year compared to the past two years as well as a historical average.  Current snow levels are lagging behind all three, where 2024 and 2025 snow levels produced well below-normal hydro supply. 

Figure 3 | Columbia Daily Snow Water Equivalent 

There is still time to catch up, but even with the rain on the way over the next week the warm temperatures mean that a larger portion of any precipitation will become immediate runoff instead of contributing to snowpack and benefiting the system later in the water year. 

We discuss this and other topics important to the Pacific Northwest hydro system in timely market flashes and other reports as part of our West Hydro Enterprise package.  Reach out to us at [email protected] for more information.

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