It’s official, the El Niño weather pattern that’s been toying and teasing Wyoming for months is dead.
The Pacific Ocean weather pattern has been sending whiplash weather through the Cowboy State for the last several months, but now meteorologists and climatologists are signaling that this iteration of the strong weather phenomenon is “dead.”
Headlines proclaiming the death and resurrection of El Niño drive Cowboy State Daily meteorologist Don Day up the wall.
“I hate the title,” he said. “‘Dead’ implies it's never coming back. We vacillate. We go back and forth. These phases change, but they'll come back again. That's why I hate it. It’s a stupid title.”
Nevertheless, even Day acknowledges that the current phase of El Niño is nearly over, and the next Pacific pattern will dominate Wyoming’s weather for the entire summer. Day said Wyomingites can expect to feel the impacts of the change.
“We're going through a phase change right now,” he said. “And one thing I've learned is that Wyoming is really, really sensitive to these changes in the Pacific.”
Farwell, El Niño — For Now
The El Niño season happens when the Pacific Ocean’s surface temperatures are warmer along the equator. Weather patterns generated over the warmer waters impact North America for several months.
The latest El Niño manifested as an unusual Modoki El Niño, where a different region of the Pacific Ocean that generally stays cool unexpectedly warmed up. That development threw a wrench in long-term weather forecasts and contributed to Wyoming’s whiplash winter, Day said.
Even then, there were signs that El Niño was starting to fade. Day said the earliest signs of a weakening El Niño could be seen as early as January.
“We started to see El Niño fade right after the first of the year,” he said. “We started to see a trend change in the weather where it was getting wetter later in the spring up north into Montana and northern Wyoming, while it was getting drier in southern Wyoming. That is something that we see when we transition from El Niño to La Niña.”
Trading Spaces
As their names imply, El Niño and La Niña are opposite phases of the same Pacific Ocean weather patterns, Day explained. El Niño is generally fast and furious, with weaker ocean surface winds spreading warmer water, while La Niña tends to last longer with stronger surface winds spreading cooler water.
Both El Niño and La Niña have one important thing in common: global impacts on weather and climate. Day said those impacts can be acutely felt across Wyoming.
“We know that an El Niño can be responsible for things being wetter and warmer in the West,” he said. “And we know, with a high degree of certainty, that La Niña patterns tend to make things drier in the West and sometimes warmer as well. But how long they last and their intensities vary. They can be around a year or go for three years. This is a natural phenomenon that has been in the Pacific for a long time.”
What that could mean for Wyoming is warm, dry seasons that could have farmers and ranchers on the lookout for potential drought conditions.
Where In Wyoming
Day said the Pacific Ocean hasn’t settled into a full-blown La Niña, but it will soon.
“We're not officially in La Niña yet, but we're close,” he said. “I can't tell you with any degree of certainty that we're going back to another three-year La Niña other than to say that we're going through a phase change right now.”
The last La Niña lasted around three years, from 2021 until early 2023, until it was replaced by the El Niño, which lasted for less than a year. The next La Niña could last one to three years, but it’s too early to say.
Historically, La Niña means dry weather in Wyoming. According to Day, that will definitely and noticeably matter as the Cowboy State transitions into summer.
“As the La Niña matures, it does tend to cover a larger area that does tend to get drier.” He said. “We’re not officially in summer yet, but for the rest of June and into July and August, with the La Niña getting stronger, that is a dry signal. It's something historically that has given us drier than normal conditions, and that is certainly a concern.”
However, Wyoming is a large enough state that the impacts of La Niña won’t be the same everywhere. Day said the disparate impacts of Wyoming’s spring weather showed how the El Niño-La Niña shift isn’t universal.
“If you go back to April, the northern counties of Wyoming have had above-average precipitation, and the southern counties were below,” he said. “It was getting wetter later in the spring up north into Montana and northern Wyoming, while it was getting drier in southern Wyoming. And that is something that we see when we transition from El Niño to La Niña. It really depends on where you are in Wyoming.”
The State Of The Summer
Based on current weather patterns and historical trends, Day anticipates that summer 2024 will be nothing like summer 2023. The incredible moisture Wyoming experienced last summer was courtesy of El Niño, and La Niña will most likely keep things dry.
“Last year was one of the wettest, greenest summers in a long, long time, and we were in a full-fledged El Niño,” he said. “This summer is trending warmer and drier, in contrast to how wet it was last year.”
Day expects northern Wyoming will continue to benefit from the last pockets of moisture generated from the end of El Niño, while southern Wyoming will continue to dry out.
And it’s already begun.
“If you look at the precipitation in the southern concern of the state since April in Cheyenne, Torrington and Wheatland into the panhandle of Nebraska, it’s dried out considerably,” he said. “Precipitation was well below average in the southern counties, while they were very high and got a lot more in the northern counties.”
Northern Wyoming endured a noticeable lack of moisture throughout the winter, while southern Wyoming received above-average snowfall, only to reverse in spring. The Sleeping Giant Ski Area in Cody closed all winter due to lack of snow and then forced to close for summer because of damage caused by extreme snow in the spring.
Day said these phenomena are expected during the El Niño-La Niña shift. Once La Niña is fully established, Day said Wyoming will trend drier overall.
“As the La Niña gets stronger, that is a dry signal,” he said. “It's something historically that has given us drier than normal conditions. For the southern and eastern parts of the state, that's certainly a concern now and for the rest of the summer. Northern Wyoming will benefit here for a little bit longer with the weather pattern being wetter, but it could turn drier as well as we go into July and August.”
What About Winter?
Wyomingites expect dry summers but anticipate and expect wet winters. With La Niña likely to settle in and stay in Wyoming over the 2024-2025 winter season, that could be an ominous sign of how much or little snow and moisture to expect.
In Day’s professional opinion, it’s much too early to anticipate what will happen during Wyoming’s next winter. There’s still too much unknown about how the incoming La Niña will manifest once this “Little Girl” fully matures into the dominant weather pattern it’s known to be.
“Indications from models are that La Niña is going to come on strong this summer, probably endure into September and October, and start to fade,” he said. “We have to be really careful with the modeling, but if that's the case, that could mean a cold winter. But if the La Niña makes it into December and January, it means a warm winter.”
There’s only definite in Day’s long-range forecast for Wyoming’s next winter: come back in September and October. Until then, El Niño is gone and Wyomingites can anticipate a warm, dry summer with La Niña.
“The models say La Niña should stay, but I've seen them be wrong and turn things off or on too quickly,” he said. “We’ve got to be cautious about any winter outlook until we get a handle on where this La Niña is going, and we need a few months before we have an idea.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
