Is the Pacific Ocean poised to deliver a dry La Niña winter to Wyoming?
Maybe. Late last week, the Climate Prediction Center (CPC) at the National Weather Service issued a La Niña Watch.
Based on current conditions and long-range weather modeling, there are indications that “a brief period of La Niña conditions is favored in the fall and early winter 2025-26,” shaking up the current neutral conditions being observed in the Pacific Ocean.
Does that mean a La Niña winter, with warmer temperatures, lower snowpack, and increased chances of drought, is on the way? Cowboy State Daily meteorologist Don Day thinks people need to consume their weather reports more carefully.
“A La Niña Watch doesn't necessarily mean a full-fledged La Niña winter, but it's being interpreted that way by people who don't know any better,” he said. “They put this out, everyone gloms onto it, and then everybody's hair is on fire, but this isn’t a slam dunk situation.”
Staying Neutral
El Niño and La Niña are opposite phases of the same weather patterns in the Pacific Ocean. El Niño is fast and furious, with weaker ocean surface winds that spread warmer water, while La Niña persists with stronger surface winds that spread cooler water.
The intensity of previous winters has been determined by the dominance of El Niño and La Niña, the ever-changing climate patterns influenced by the water temperatures of the Pacific Ocean, known as the El Niño-Southern Oscillation (ENSO).
In Wyoming, El Niño tends to bring warm, wet weather, while La Niña tends to dry things out. The implications of either system are enormous on everything from the agricultural industry to the intensity of wildfires.
Currently, the Pacific Ocean is ENSO-neutral. Neither pattern is dominant, which also has a historical precedent for longer, colder, and snowier winters in Wyoming.
That neutral pattern is what Day factored into his long-range forecast for Winter 2025-2026. And, despite the CPC’s La Niña Watch, he’s sticking to it.
“Will there be a short-lived La Niña-like episode this fall? Yes, but it's not going to change anything in terms of what our long-range forecasts have been talking about,” he said.
The Long And Short Of It
Day is taking the La Niña Watch for what it is: a watch, rather than a warning. While the Pacific Ocean is developing conditions similar to a La Niña, Day believes it’s too little and too late to impact long-range forecasts.
“Timing plays a huge role in determining how the winter season will go,” he said. “You’ve got to have multiple months of the temperature anomaly, more than a half a degree Centigrade below the average, for a La Niña to be really impactful.”
Winter 2024-2025 was a full-fledged La Niña winter. It ramped up and reached its peak strength in December and January, then started transitioning into the ENSO-neutral from March to June.
Day said a similar pattern is being observed in the Pacific Ocean, but the timing is different. That’s critical in determining the impact of any La Niña or El Niño.
“What's happening is that it’s getting stronger in September and October, and then fading at the same time the La Niña was gaining strength last year,” he said. “They're not exactly the same every year, and their impacts are not exactly the same every year. The intensities vary, and understanding that is very important.”
If there are any impacts, Day anticipates they’ll be short-term. Ironically, despite the La Niña Watch they issued, the CPC would agree with that assessment.
“Their report says most models favor ENSO-neutral status to prevail through the fall and winter of 2025 and 2026,” Day said. “They’re not predicting a full-fledged La Niña, which is basically saying the same thing I'm saying. But they've issued a La Niña Watch, so go figure.
Where It Matters Most
LeAnn Miller, local food broker for Eat Wyoming, "Wyoming's virtual farmers market,” which matches state producers to Wyoming consumers, said farmers are looking forward to the rains La Niña could bring to northern regions of the country.
Many areas, especially the eastern parts of the state, have been in a drought for several years, and she said sustained rains might help pull them out of it.
“We’ve been in a drought for more than a couple of years — for a long time,” she said. “The rainfall will be welcome if we get enough. More rain will make my producers happy.”
While she is hoping for steady rain, Miller added that she doesn't wish for it all at once with harvest time around the corner.
“Now, as long as it’s not constant rain, because when it rains, they can’t harvest. It’s wet and muddy,” she said. “It has to be that happy place.”
Meanwhile, Dennis Sun, publisher of the Wyoming Livestock Roundup, said most ranchers are “kind of confused” by the La Niña Watch.
“From the get-go, we've heard it's going to be a tough winter, but then the Poor Farmer’s Almanac said it’s going to be a mild winter,” he said. “I don’t think anyone’s worried about it now, as we’re just getting into fall, but we’ve got to be prepared.”
Sun said ranchers and farmers don’t like making seasonal decisions “on the fly,” but they’re ready to shift their strategies or make whatever in-the-moment decisions are necessary. There could be hardships, but experienced producers are ready for anything.
“In ranching or any type of agriculture, you plan for the worst and hope for the best,” he said. “You can usually change pretty quickly, but you’ve got to have something saved so you aren’t surprised by a bad winter.”
Sun expects most ranchers and farmers will be keeping a closer eye on the weather, but it’s too early to be intimidated by the La Niña Watch.
“I’ll tell you how the winter’s going in six months,” he said.
Run The Numbers
Day’s message to anyone concerned about the La Niña Watch isn’t that they shouldn’t read into it too much. If anything, many people aren’t reading into it enough.
“The statistical probability of a full-fledged La Niña between October and December is less than 60%,” he said, “That drops to less than 50% for December, January, and February, and then it decreases to less than 40% for January, February, and March.”
Those statistics support Day’s assessment that the impacts of whatever’s happening in the Pacific Ocean will be short-term. Even the CPC believes most of Winter 2025-2026 will be ENSO-neutral.
“Yes, we may go into a brief, colder La Niña-like status this fall, but it's not likely to carry forward into winter,” Day said. “This is one of these situations where if the dam breaks, everyone's going to think it's going to be a La Niña winter. I don't think so. A lot of people don't think so. If you read the advisory, they don't think so.”
Day will be ready to update his long-range forecast as needed. However, he doesn’t anticipate that he’ll need to.
“Based on what we're seeing, I am not expecting a La Niña winter,” he said. “That’s the difference between a watch and a warning.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
