La Niña has ended, ENSO-Neutral conditions favored into Fall 2025

The latest update from the NOAA Climate Prediction Center declared that La Niña has ended in the Pacific Ocean. We noted in some recent episodes of the Comedeorological Report that this was coming as sea surface temperatures along the equator had warmed.

La Niña is the cold phase of the El Niño-Southern Oscillation, which is driven by sea surface temperatures along the equator in the Pacific Ocean. The warm phase is El Niño while being near average is commonly called ENSO-Neutral.

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Last winter’s La Niña was fairly weak despite early forecasts calling for a strong event. Development was delayed, with one possible factor behind this being very warm ocean temperatures throughout the planet. During the fall months, updated forecasts improved significantly.

La Niña’s death during spring of 2025 has been well-modeled for several months. Data shows that we are likely to remain in ENSO-Neutral conditions through the summer months with neutrality also favored this fall. A bias toward neutral conditions remains in the modeling through winter 2025-26 but confidence decreases the further into the future we look.

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Looking toward the summer, some years with similar ENSO conditions are 2018, 2006, and 2001. Where this year goes will depend on more factors than just ENSO but this can give us some foresight in what to expect. These three years appear appropriate as they all brought ENSO-Neutral summers after a weak La Niña.

Last month I published an article that drew heavily on 2022 as an analog year for this summer. In general my view remains similar to last month’s article. I think out of the four years we’re considering, 2001 is the worst match for the Pacific Northwest as sea surface temperatures in the Gulf of Alaska were well below average during the spring instead of being above average as they are now.

It is worth noting that Summer 2001 also stands out against the other three years we’re considering in that Pacific Northwest temperatures were generally below average with well above average precipitation in and west of the Cascades. as well as in the B.C. Rockies.

The rest (2006, 2018, 2022) were relatively hot and dry summers in the Northwest and British Columbia. One exception here is that thunderstorm activity in Central Oregon and the Columbia Basin was enhanced during 2022.

A warm and dry summer following this moist spring we are having brings significant wildfire risk. Snowpack in Washington and British Columbia has improved over the last few weeks but we haven’t completely made up the deficit.

Moist weather in the spring and early summer allows for rampant growth in the understory of forests and of the grasses in arid regions. As this brush dries, it becomes fuel for wildfires. Fire season starts getting under way in May or June in the inland deserts and not long after in the mountains and forests.

A quick drying and warming can exasperate conditions by turning brush into fuel early in the season while also accelerating snowmelt. In the United States, nearly 90% of wildfires are caused by human activity. Dry fuels increase the risk of fire starts as well as the risk of them spreading rapidly.

The further north one gets in British Columbia the lower the population density, though human-started fires are possible anywhere. Dry thunderstorms become a significant threat during the second half of the summer in the B.C. Interior.

Aside from the fire risk, water supply is looking limited for this summer. Washington recently issued a drought emergency for most of the state. Kennewick Irrigation District is planning to request users to follow a voluntary watering schedule. Water supply for the Yakima Valley has improved in the last few weeks but remains below what was seen last year.

ENSO-Neutral years tend to bring the more activity during the Pacific Northwest fall storm season. If these conditions can be held onto into fall as models indicate, we could be in for multiple strong regional storms like the region experienced during Fall 2024. There is not a strong enough signal to discuss how this winter may look.

The featured image is sea surface temperature anomalies in the Pacific on April 9, 2025. (NOAA)