Cool Tropical Pacific & Warm North Pacific Waters: How will the PNW snowpack respond?
In the winter of 2024–25, we learned firsthand that a weak La Niña doesn’t necessarily deliver the cool and wet conditions that fuel the deep, mid-winter snowpacks we all hope for.
Before diving into this year’s outlook—how it compares, and what other predictors might carry weight—let’s revisit the El Niño–Southern Oscillation (ENSO), the cyclical fluctuation in tropical Pacific sea surface temperatures that shapes global weather patterns. ENSO cycles through three distinct phases: El Niño (warm), La Niña (cool), and Neutral conditions. So how do the October forecasts for mid-winter ENSO probabilities compare between this upcoming cool season and the most recent one? The distributions are strikingly similar, with only a subtle weakening of the La Niña signal for 2025–26. Both forecasts suggest the highest odds for cool-phase conditions during autumn and early winter.
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